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Geant4 User's Guide for Toolkit Developers

1. theParticleTable G4ParticleDefinition g4ParticleDefinition i n G4ProcessManager theProcessManagerShado theDecayTabl G4DynamicParticle theParticleDefinition G4OpticalPhoton G4SigmaPlus li Figure 2 15 Particle classes G4ParticleTable G4VisotopeTable GetParticleTable G4ParticleTable 7 GetlonTableQ G4lonTable G4NuclideTable G4NuclideTable Getinstance GetNuclideTable WorkerG4lonTableQ GenerateNuclide L PreloadNuclide SetThresholdOfHalfLife t Getlon Z A lvl AddState p 71 p 72 p 73 p 74 p 75 p 76 GetNucleusMass Z A L lvl GetlsotopeBylsoLvi Z A Ivi G4ThreadLocal G4lonList GetlsomerMass Z A lvl GetLifeTime p_49 SESS i Insert particle flonTable G4lsotopeList G4NucleiP rti abi cdi G4NucleiPropertiesTheoreticalTable GetNuclearMass A Z IsinStableTable A Z BindingEnergy A Z G4NucleiPropertiesTableAME03 Figure 2 16 Particle Table G4ParticleDefii currentParticle WorkerG4ParticleTable GetParticle FindParticle G4lonTable Getiterator G4PTbiDictterator WorkerG4lonTable GetParticleTableO Pi i CheckReadinessQ i BAL GetlonTable G4ThreadLocal G4PTbIDictionary GetNucleusMass Insert GetlsomerMass GetLifeTime o Insert G4PTblEncodingDictionary Figure 2 17 Particle
2. void FreeWorker TE offset 0 return i delete offset y Let s consider a function that can be called concurrently by more than one thread tinclude G4Class hh Variables at global scope G4Class a G4Class b void Eoo a SetMyData 0 1 First instance b SetMyData 0 2 Second instance G4cout lt lt a GetMyData lt lt lt lt b GetMyData lt lt G4endl We expect that each thread will write on the screen 0 1 0 2 When we declare the variable a the static object subInstanceManager in memory has the state 38 Design and Function of Geant4 Categories totalobj 0 TLS workertotalspace 0 TLS offset NULL The constructor of G4Class calls CreateSubInstance and since at this point totalobj equals 1 G4Splitter NewSubinstances is called This will create a buffer of 512 pointers of type G4ClassData each of which is initialized via G4ClassData initialize to the value 1 Finally G4Splitter CreateSubInstance returns 0 and a gClassInstanceld equals 0 When a SetMyData 0 1 is called the call is equivalent to subInstanceManager offset 0 fValue 0 1 When now we declare the instance b the procedure is repeated except that since totalobj now equals 1 and workertotalspace is 512 there is no need to call G4Splitter NewSubInstances and we use the next available array position in offset Only if we create more than 512 instances of G4Class is the memory array re
3. thread shared data field thread local data field Figure 2 28 The eight possible scenarios for sharing of objects 2 14 3 2 1 Case A thread local class instance s thread shared and instance shared data field In this case each thread has its own instance s of type G4Class We need to share fValue both among threads and among instances As for a sequential application we can simply add the static keyword to the declaration of fValue This technique is common in Geant4 but has the disadvantage that the resulting code is thread unsafe unless locks are used Trying to add const or modify its value with the use of a lock only outside of the event loop is the simplest and best solution class G4Class static const G4double fValue y 2 14 3 2 2 Case B thread local class instance s thread local and instance shared data field This scenario is also common in Geant4 we need to share a variable e g a data table between instances of the same class However it is impractical or it would lead to incorrect results if we share among threads fValue i e the penalty due to the need of locks is high or the data field holds a event dependent information To make the code thread safe we mark the data field thread local via the keyword G4ThreadLocal 35 Design and Function of Geant4 Categories tinclude G4Types hh class GAME static G4ThreadLocal G4double fValue It should be noted that only simple data types can be
4. UserSteppingAction fUserSteppingAction Q0 1 0 1 fVerbose Figure 2 5 Tracking design G4TrackingManager is an interface between the event and track categories and the tracking category It handles the message passing between the upper hierarchical object which is the event manager G4EventManagerz and lower hierarchical objects in the tracking category G4TrackingManager is responsible for processing one track which it receives from the event manager G4TrackingManager aggregates the pointers to G4SteppingManager G4Trajectory and G4UserTrackingAction It also has a use relation to G4Track G4SteppingManager plays an essential role in particle tracking It performs message passing to objects in all categories related to particle transport such as geometry and physics processes Its public method Stepping steers the stepping of the particle The algorithm employed in this method is basically the same as that in Geant3 The Geant4 implementation however relies on the inheritance hierarchy of the physics interactions The hierarchical design of the physics interactions enables the stepping manager to handle them as abstract objects Hence the manager is not concerned with concrete interaction objects such as bremsstrahlung or pair creation The actual invocations of various interactions during the stepping are done through a dynamic binding mechanism This mechanism shields the tracking category from any change in the desi
5. 2 12 6 1 1 Visibles If the vis attributes pointer is zero drivers should pick up the default vis attributes from the viewer const G4VisAttributes pVisAtts visible GetVisAttributes if pVisAtts pVisAtts fpViewer GetViewParameters GetDefaultVisAttributes where visible denotes any visible object polyhedron circle etc There is a utility function G4V Viewer GetA pplicableVisAttributes which does this so an alternative is const G4VisAttributes pVisAtts fpViewer GetApplicableVisAttributes visible GetVisAttributes Confusingly there is a utility function G4VSceneHandler GetColour which also does this so if it s only colour you need the following suffices 28 Design and Function of Geant4 Categories const G4Colour amp colour GetColour visible but equally well const G4VisAttributes pVisAtts fpViewer GetApplicableVisAttributes visible GetVisAttributes const G4Colour amp colour pVisAtts GetColour or even const G4VisAttributes pVisAtts visible GetVisAttributes ao pVasAEES pVisAtts fpViewer GetViewParameters GetDefaultVisAttributes const G4Colour amp colour pVisAtts GetColour 2 12 6 1 2 Text Text is a special case because it has its own default vis attributes const G4VisAttributes pVisAtts text GetVisAttributes if pVisAtts pVisAtts fpViewer GetViewParameters GetDefaultTextVisAttributes const G4Colour amp colour pVisAtts
6. 3 3 1 Properties of particles sire A A AI e ROS 51 3 32 Adding New Particles 3 oc oer er dot ere tesoro pere dee apa 52 3 3 3 Nuclide properties from Evaluated Nuclear Structure Data File 0 0 0 0 eee 52 3 4 Electromagnetic PHYSICS titanio reitera Ud Pede ee dosis 53 3 3 Hadronic PHYSICS tese e Re Uri E Rep edo PEE 54 3 5 T introduction 36 rore ie ett e teh ont ied edes ceto ure ende amodo potes tree 54 3 5 2 Principal Considerations d oce e ope edere a Pep ee eee eer 54 3 3 3 Level 1 Framework processes iiie iecit Etpe lost ise eR EER TER 54 3 5 4 Level 2 Framework Cross Sections and Models ocooocccccnnccnnccnocnnccnnconnccnnccnnconnconncos 55 3 5 5 Level 3 Framework Theoretical Models sese 58 3 5 6 Level 4 Frameworks String Parton Models and Intra Nuclear Cascade 60 3 5 7 Level 5 Framework String De excitation sess eme 61 3 5 8 Creating Your Own Hadronic Process oooccooccnccnnccnncnnccnnconnconnccnnconnconnconncnnncnnncnnronase 62 3 6 Generic Event Biasing o oer ene oe deb Rei gy eo obe e aedes Ene gie eee cos e PIDE e S Rd deep 64 3 6 1 Introduction e A ee e o o TE eed dU eni et ete ETE 64 3 62 Design of Generic Brasing doeet emer yes hase deed cesta eel des ee idee E I 65 3 6 3 Physics Process Occurence Biasing sssessesseseeee eme He mH ene 66 327 VISUALISATION NC 67 3 7 1 Creating a new graphics driver meore n enni
7. A simplified garbage collection mechanism without reference counting is implemented include G4AutoDelete hh void G4Class bar Get a thread local value G4Something local fValue Get if local 0 local new G4Something G4AutoDelete Register local All thread instances will be delete automatically This technique will delete all instances of the registered objects at the end of the program after the main function has returned if they were declared static This method has several limitations i Registered objects will be deleted only at the end of the program ii The order in which objects of different type will be deleted is not specified iii Once an object is registered it cannot be deleted anymore explicitly by user iv The objects that are registered with this method cannot contain data filed marked G4ThreadLocal and cannot be a split classes v Registered object cannot make use of G4Allocator functionalities vi These restrictions apply to all data members for which the class owns property In addition since the objects will be deleted in a non specified order after the main program exit it is recommended to provide a very simple destructor that does not depend on other objects in particular should not call any kernel functionality 2 14 3 4 3 Thread Private singleton In Geant4 the singleton pattern is used in several cases The majority of the managers are implemented via the s
8. ScomputeStep virtual Leve SLevelLocate lt lt const gt gt ComputeTrans woxelLocate aramVoxelLocate b lt lt const gt gt DistanceToOut const Inside LevelLocate Figure 2 13 Class diagram for the navigator 16 Design and Function of Geant4 Categories Status of this chapter 2 8 Electromagnetic Fields The object oriented design of the classes related to the electromagnetic field is shown in the class diagram of Figure 2 14 The diagram is described in UML notation G4TransportationManager from navigation H lt lt const gt gt GetFieldManager b lt lt const gt gt GetNavigatorFo G4Transportation const GetPropagatorl from processes static GetTransporta 1 gt 1 fNavigatorrorTracking fFieldManager G4Navigator from navigation a0 G4FieldManager f PropagatorInFiell createChordFinder Orsay NN DoesFieldExist fDetectorFieldMgr GetDetectorField fNavigator fC rrentFieldMgr 1 fChordFinder 0 G4ChordFinder AdvanceChordLimited HcetDeltaChord GetIntegrationDriver setDeltaChord setintegrationDriver Figure 2 14 Electromagnetic Field 2 9 Particles 2 9 1 Design Philosophy The particles category implements the facilities necessary to describe the physical properties of particles for the simulation of particle matter i
9. a multi threaded equivalent of G4RunManagerKernel The new run manager class G4WorkerRunManager that inherits from G4RunManager implements the worker model It uses the mandatory class G4WorkerRunManagerKernel the worker equivalent of G4RunManagerKernel The new user initialization class G4VUserActionInitialization is responsible for the instantiation of thread local user actions 31 Design and Function of Geant4 Categories The new user initialization class GAUserWorkerlnitialization is responsible for the initialization of worker threads Additional information on Geant4 multi threading model can be found in the next section In this chapter after a brief reminder of basic design choices we will concentrate on aspects that are important for kernel developers particularly the most critical aspects for multi threading in Geant4 memory handling split classes and thread local storage In the following it is assumed that the user is already familiar with the general aspects of multi threading The section Additional Material provides more information on this topic 2 14 2 General Design Geant4 Version 10 0 introduces parallelism at the event level events are tracked concurrently by independent threads The parallelism model is master worker in which one or more threads are responsible of performing the simulation while a separate control flow controls and steers the work A diagram of the general overview of a multi threaded
10. make available several utilities and reduce unneccesary code duplication In the latter recommended approach the user must in general develop as many as three classes a process a cross section and a model Instances of the cross section and model classes must then be assigned to the process In practice it is usually necessary to develop only a model class or a cross section class since a number of processes are already provided by Geant4 Before writing any code users should check that Geant4 has not already povided the necessary models cross sections or processes 3 5 8 1 Developing a new hadronic model A hadronic model is repsonsible for the generation of a set of final state four vectors given an initial projectile and target New models should derive from the G4HadronicInteraction base class and at least two methods in this class must be implemented virtual G4HadFinalState ApplyYourself const G4HadProjectile amp aProjectile G4Nucleus amp targetNucleus which is responsible for generating the final state of the interaction including the specification of all particle types and four momenta and virtual G4bool IsApplicable const G4HadProjectile amp aProjectile G4Nucleus amp targetNucleus which is responsible for checking that the incident particle type and energy and the Z and A of the target nucleus can be adequately handled by the model G4HadronicInteraction provides a number of utilities to aid in the implementation of
11. v G4PloyconeSide vi G4PolyhedraSide For Physics related split classes the classes G4PDefSplitter and G4VUPLSplitter implement the split class mechanism These are the physics related split classes i G4ParticleDefinition ii G4VUserPhysicsList iii GIVModularPhysicsL ist iv G4VPhysicsConstructor 39 Design and Function of Geant4 Categories 2 14 3 4 Explicit memory handling In the following some utility classes and functions to help memory handling are discussed Before going into detail it should be noted that all of these utilities have a small CPU and memory performance penalty they should be used with caution and only if other simpler methods are not possible In some cases limitations are present 2 14 3 4 1 The template class G4Cache In many cases the full functionality of split classes is not needed and what we really want are independent thread local and instance local data fields in thread shared instances of G4Class A concrete example would be a class representing a cross section that is made shared because of its memory footprint It requires a data field to act as a cache to store the value of a CPU intensive calculation Since different threads share this instance we need to transform the code in a manner similar to what we do for the split class mechanism The helper class G4Cache can be used for this purpose note that the complication of the initial value of the thread local data field is not present in this c
12. Allow to adapt event generators ex PYTHIA7 state production in shower simulation Allow for combination of the above with any intra nuclear transport INT Allow stand alone use of intra nuclear transport Allow for combination of the above with any pre compound model Allow stand alone use of any pre compound model Allow for use of any evaporation code Allow for seamless integration of user defined components for any of the above 96 O tA RU t Design and interfaces To provide the above flexibility the following abstract base classes have been implemented e G4VHighEnergyGenerator e G4VIntranuclearTransportModel e G4VPreCompoundModel G4VExcitationHandler In addition the class G4 TheoFS Generator is provided to orchestrate interactions between these classes The class diagram is shown in Figure 3 5 G4VHighEnergy Generator serves as base class for parton transport or parton string models and for Adapters to event generators This class declares two methods Scatter and GetWoundedNucleus The base class for INT inherits from G4Hadronic Interaction making any concrete implementation usable as a stand alone model In doing so it re declares the ApplyYourself interface of GaHadronic Interaction and adds a second interface Propagate for further propagation after high energy interactions Propagate takes as arguments a three dimensional model of a wounded nucleus and a set of secondaries with energie
13. Geant4 application is shown here Geometry and Physics configuration Per event seeds pre prepared in a queue Per thread Per thread Per thread Init Init Init Threads compete for next event to be processes new in ref 08 End Local End Local End Local Run Run Run Command line scoring and G4tools automatically merge results from threads Merge in Global Run Figure 2 26 Simplified schema of the master worker model employed in Geant4 The user interacts with the master which is responsible for creating and controlling worker threads Before the simulation is started per event seeds are generated by the master This operation guarantees reproducibility Once threads are spawned and configured each worker is responsible for creating a new G4Run and for simulating a subset of the events At the end of the run the results from each run are merged into the global run Details on how to interact with a multi threaded simulation are discussed in the Guide for Application Developers Geant4 parallelization makes use of the POSIX standard The use of this standard in Geant4 guarantees maximum portability between systems and integration with advanced parallelization frameworks for example we have verified that this model co works with TBB and MPI To effectively reduce the memory consumption in a multi threaded application workers share instances of objects that consume the majority of memory geometry and physics tables work
14. QMD invariant phase space decay CHIPS and fast parametrised models for calorimeter materials with user defined modeling of interactions of spallation nucleons with the most abundant tracker and calorimeter materials Isotope production The G4HadronicProcess by default calculates the isotope production information from the final state given by the transport model In addition it provides a registering mechanism for isotope production models that run in parasitic mode to the transport models and inherit from GAVIsotope Production The registering mechanism behaves like a FILO stack again based on Chain of Responsibility The models will be asked for isotope production information in inverse order of registration The first model that returns a non NULL value will be applied In addition the G4Hadronic Process provides the basic infrastructure for accessing and steering of isotope production information It allows to enable and disable the calculation of isotope production information globally or for individual processes and to retrieve the isotope production information through the G4IsoParticleChang GetIsotopeProductionInfo method at the end of each step The G4HadronicProcess is a finite state machine that will ensure the GetIsotope ProductionInfo returns a non zero value only at the first call after isotope production occurred An example of the use of this functionality is the study of activation of a Germanium detector in a high precisio
15. activate addNewDetector get collectionCapacity G4EventManage r G4VICmessen G4Event 1 G4SDmessenger y manager AV tom EventManagemer ger e get collectioniD orn a arena rom Intercom prepareNenEvent rom Evenil anagoment A erminateCurrentEvent edd hileCollecton 1 get_HCofThisEvent me 2 o G4HCtableEI G4SteppingMan norit tresTop ager H s from Tracking 1 t 1 P Aa G4SDStructure G 4LogicalVolume manager eT G4HCofThisEvent from Geometry addNewDetector add hitsCollection getSD get HC initalize get capacity terminate get numberOfCollections e 1 y X detector 1 e SensitiveDetector ET E a HC G4VSensitiveDetector event GaStep acivate m from Tracking clear drawAI G4VHitsCollection ndo venti 1 il SDnamo G4Strin 9 getColectonNamey acoltection 5 11 SDpathName G4String getName Ii collectionName G4String so gelPalhiNamel 1 get numberOfCollections e S esso initatzet 5 NC IUS Geometry isActive print G4VHit dan Y processHits drew print Ww Figure 2 8 Overview of hit classes management Theso dorived classes are just examples Implementations should be done by GavsSensillveDetector activate GAVHitsCollection drawal i o users accoring to their actual endOtEvent EN detector setups aetName 39 1 process poe t S dk 1 ak j Y calorimeterHi
16. class defining the interface for each Random engine Its pure virtual methods must be defined by its subclasses representing the concrete Random engines e HepJamesRandom class inheriting from HepRandomEngine and defining a flat random number generator according to the algorithm described in F James Comp Phys Comm 60 1990 329 This class is instantiated by default as the default random engine DRand48Engine class inheriting from HepRandomEngine and defining a flat random number generator according to the drand48 and srand48 system functions from the C standard library RandEngine class inheriting from HepRandomEngine and defining a flat random number generator according to the rand and srand system functions from the C standard library RanluxEngine class inheriting from HepRandomEngine and defining a flat random number generator according to the algorithm described in F James Comp Phys Comm 60 1990 329 344 and originally implemented in FORTRAN 77 as part of the MATHLIB HEP library It provides 5 different luxury levels 0 4 RanecuEngine class inheriting from HepRandomEngine and defining a flat random number generator according to the algorithm RANECU originally written in FORTRAN 77 as part of the MATHLIB HEP library It uses a table of seeds which provides uncorrelated couples of seed values HepRandom the main class collecting all the methods defining the different random generators applied to HepRandom
17. decays of all long lived unstable particles are handled by a single process This process gets the step length from the mean life of the particle The generation of decay products requires a knowledge of the branching ratios and or data distributions stored in the particle class The electromagnetic sub category is divided further into the following packages standard handling basic properties for electron positron photon and hadron interactions lowenergy providing alternative models extended down to lower energies than the standard package dna providing DNA physics and chemistry simulation highenergy providing models for rare high energy processes muons handling muon interactions and energy loss propagator xrays providing specific code for x ray physics optical providing specific code for optical photons utils collecting utility classes used by the above packages It provides the features of openness and extensibilty resulting from the use of object oriented technology alternative physics models obeying the same process abstract interface are often available for a given type of interaction For hadronic physics an additional set of implementation frameworks was added to accommodate the large number of possible modeling approaches The top level framework provides the basic interface to other Geant4 categories It satisfies the most general use case for hadronic shower simulations namely to provide inclusiv
18. declared G4ThreadLocal More information and the procedures to make an object instance thread safe via thread local storage are explained in this web page 2 14 3 2 3 Case C thread local class instance s thread shared and instance local data field One possible use case is the need to reduce the application memory footprint providing a component to the thread local instances of G4Class that is shared among threads e g a large cross section data table that is different for each instance Since this scenario strongly depends on the implementation details it is not possible to define a common strategy that guarantees thread safety The best option is to try to make this shared component const 2 14 3 2 4 Case D thread local class instance s thread local and instance local data field This case is the simplest nothing has to be changed in the original code 2 14 3 2 5 Case E thread shared class instance s thread shared and instance shared data field With respect to thread safety this case is equivalent to Case A and the same recommendations and comments hold 2 14 3 2 6 Case F thread shared class instance s thread local and instance shared data field Concerning thread safety this case is equivalent to Case B and the same recommendations and comments hold 2 14 3 2 7 Case G thread shared class instance s thread shared and instance shared data field Since the class instances are shared among threads the data field
19. generators 14 0 G4PrimaryGenerator G4DynamicParticle generatePrimaryVertex Vertex G4PrimaryVertex vertex G4PrimaryVertex point G4ThreeVector 1 from PhysicsProcess time G4double d particles insert G4UserPrimaryGen Y x erator 4 A 1 A 0 n G4ParticleDefinition G4DynamicParticle G4ParticleGun from ParticleDefinition from ParticleDefinition set particle definition set particle energy sel parlicle momentum set particle position e el File users kurasiae ROSE2 a40831 md Thu Aua 31 19 58 30 1995 Class Diaaram EventGenerator Main Figure 2 4 Event Generator Status of this chapter 27 06 05 design philosophy section added from Geant4 general paper by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 4 Tracking The tracking category manages the contribution of the processes to the evolution of a track s state and provides information in sensitive volumes for hits and digitization 2 4 1 Design Philosophy It is well known that the overall performance of a detector simulation depends critically on the CPU time spent propagating the particle through one step The most important consideration in the object design of the tracking category is maintaining high execution speed in the Geant4 simulation while utilizing the power of the object oriented approach An extreme approach to the particle tracking design would be to int
20. gets the cross section as a function of particle type energy and target material and converts it to a mean free path which is in turn passed on to the tracking This method can be quite simple G4double particle aTrack GetDynamicParticle G4double material aTrack GetMaterial return factor theCrossSectionDataStore gt GetCrossSection particle material provided an appropriate cross section data set is already available in the data store The above discussion refers to in flight processes At rest hadronic processes do not currently derive from G4HadronicProcess but from G4VRestProcess or G4VRestDiscreteProcess As such they do not employ the full hadronic framework and must be implemented directly without models The methods to be implemented are similar to those in the in flight case virtual G4VParticleChange AtRestDoIt const G4Track amp const G4Step amp and G4bool IsApplicable const G4ParticleDefinitions 3 6 Generic Event Biasing 3 6 1 Introduction This section presents the generic biasing classes which have been introduced since release 10 0 Theses classes are meant to virtually allow any type of process level based biasing In 10 0 and 10 1 only Post Step biasing actions are possible which allows Physics process biasing of 64 Extending Toolkit Functionality e occurence law ie biasing acting on the process Post StepGetPhysicallnteractionLength level final state production ie biasin
21. i SSettimeStp GetOuterRadius SetParticleType CVrarticleScatiorer j lt amp StopTimeLoop GetNuclearRadius nj SetParticieTypet SGetTimeToInteraction heckPauliPrinciple GetNuclearRadius qe t SScatter _ FindFragments poLorentzBoost Are YouHit UpdateKineticTrack loLorentzBoost DoTimeStep y DoLorentzContraction DoLorentzContracti lon DoTranslation G4ParticleScatterer Y qf StartLoop G4VFieldPropagation Sf GetNextNucleon Transport amp MirrorNucleons GetExcitationEnergy a Init G4Fancy3DNucleus Figure 3 7 Level 4 implementation framework of the hadronic category of Geant4 intra nuclear transport aspect The use cases of this level are related to commonalities and detailed choices in string parton models and cascade models They are use cases of an expert user wishing to alter details of a model or a theoretical physicist wishing to study details of a particular model Requirements 1 Allow to select string decay algorithm 2 Allow to select string excitation 3 Allow the selection of concrete implementations of three dimensional models of the nucleus 4 Allow the selection of concrete implementations of final state and cross sections in intra nuclear scattering 60 Extending Toolkit Functionality Design and interfaces To fulfil the requirements on string models two abstract classes are provided the G4VParton StringModel and the G4VStr
22. is discussed in more details below Section 3 6 3 virtual G4VParticleChange ApplyFinalStateBiasing const G4BiasingProcessInterface callingProcess const G4Track track const G4Step step G4bool amp forceBiasedFinalState 0 which is meant for final state biasing the biasing operation gets called by the GaBiasingProcessInterface callingProcess and has to return a biased particle change This one should take care of providing the proper weight values for the biasing applied methods for non physics biasing virtual G4double DistanceToApplyOperation const G4Track track G4double previousStepSize G4ForceCondition condition 0 which returns the distance at which the operation must be applied and returns also the force condition for this the returned values distance force condition are returned to the stepping manager by the the G4BiasingProcessInterface callingProcess to make the biasing opetation to compete for limiting the step virtual G4VParticleChange GenerateBiasingFinalState const G4Track track const G4Step step 0 called if the operation has limited the step must return the final state generated by the operation 3 6 2 2 The G4VBiasingOperator Interface Class The G4VBiasingOperator class is meant to define the interface to pilot biasing operations It selects biasing operations or sequences of biasing operations to build
23. lt lt Concrete gt gt lt lt Purely Abstract gt gt G4lsoParticleChange G4VIsotopeProduction Getlsotope lt lt Conerete gt gt G4NeutronlsotopeProduction Figure 3 4 Level 2 implementation framework of the hadronic category of Geant4 isotope production aspect The three parts are integrated in the GaHadronic Process class that serves as base class for all hadronic processes of particles in flight Cross sections Each hadronic process is derived from G4Hadronic Process which holds a list of cross section data sets The term data set is representing an object that encapsulates methods and data for calculating total cross sections for a given process in a certain range of validity The implementations may take any form It can be a simple equation as well as sophisticated parameterisations or evaluated data All cross section data set classes are derived from the abstract class GAVCrossSection DataSet which declares methods that allow the process inquire about the applicability of an individual data set through IsApplicable const G4DynamicParticle const G4Element and to delegate the calculation of the actual cross section value through GetCrossSection const G4DynamicParticle const G4Element Final state production The G4HadronicInteraction base class is provided for final state generation It declares a minimal interface of only one pure virtual method GaVParticleChange ApplyYourself const G4T
24. notation G4VisManager G4Ulmanager visManager 1 UlManag r G4Ulxvt Gaug EXIT and other control commands Guis session s GaUlcontroi CASA Messenger d treeTop G4Ulses 1 E B geComm k 1e messenger A These two classes are shown just for illustrating how classes in other categories use the messenger G4Ulbatch n 2 messengerA should know all of G4U terminal Q nessesary set get methods of classA and should be written by the 1 auther of classA command guidance messenger G4Ulcommand e G4Ulparameter E parameter Figure 2 25 Overview of intercom classes Status of this chapter 27 06 05 design philosophy from Geant4 general paper and class design sections added by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 14 Parallelism in Geant4 multi threading capabilities 2 14 1 Event level parallelism Geant4 event level parallelism is based on a master worker model in which a set of threads the workers are spawned and are responsible for the simulation of events while the steering and control of the simulation is given to an additional entity the master Multi threading functionalities are implemented with new classes or modifications of existing classes in the run category e The new run manager class G4MTRunManager that inherits from G4RunManager implements the master model It uses the mandatory class G4MTRunManagerKernel
25. order to cache the computed value and therefore reuse it for future calls to the method and to eventually implement a precise computation of the solid s surface area If the method will not be overloaded the default implementation from the base class will be used estimation through a Monte Carlo algorithm and the computed value will not be stored There are a few member functions to be defined for the purpose of visualisation The first method is mandatory and the next four are not Mandatory virtual void DescribeYourselfTo G4VGraphicsScene amp scene const 0 Not mandatory virtual G4VisExtent GetExtent const virtual G4Polyhedron CreatePolyhedron const virtual G4NURBS CreateNURBS ONC OnSite virtual G4Polyhedron GetPolyhedron Egon What these methods should do and how they should be implemented is described here void DescribeYourselfTo G4VGraphicsScene amp scene const This method is required in order to identify the solid to the graphics scene It is used for the purposes of double dispatch All implementations should be similar to the one for G4Box void G4Box DescribeYourselfTo G4VGraphicsScene amp scene const scene AddSolid this b The method 47 Extending Toolkit Functionality G4VisExtent GetExtent const provides extent bounding box as a possible hint to the graphics view You must create it by finding a box that encloses your solid and returning a VisExtent that is c
26. pVisAttribs pSol DescribeYourselfTo sceneHandler gt sceneHandler AddSolid this sceneHandler PostAddSolid sceneHandler PreAddSolid theAT pVisAttribs gt BeginPrimitives fpObjectTransformation gt pPolyhedron solid GetPolyhedron if the scene handler implements its own AddSolid Moreover the sequence BeginPrimitives fpObjectTransformation AddPrimitive pPolyhedron EndPrimitives can be invoked without a prior PreAddSolid etc The flag ProcessingSolid will be false for the last case The possibility of any or all of these three scenarios occurring for both permanent and transient objects affects the implementation of a scene handler if there is any attempt to build a graphical database This is reflected in the templates XXXStored and XXXSG described in Section 3 7 1 1 1 Transients are discussed in Section 3 7 1 6 G4TrajectoriesModel At end of event the trajectory container is unpacked and for each trajectory sceneHandler AddCompound called The scene handler may implement this virtual function or inherit void G4VSceneHandler AddCompound const G4VTrajectory amp traj traj DrawTrajectory G4TrajectoriesModel fpModel gt GetDrawingMode Similarly the user may implement DrawTra ject ogy or inherit void G4VTrajectory DrawTrajectory G4int i mode const Extending Toolkit Functionality pVVisManager gt DispatchToModel this i mode
27. safe messenger to model interaction on the command line the messengers should inherit from G4VModelCommand Concrete factories must implement one pure virtual function 27 Design and Function of Geant4 Categories virtual ModelAndMessengers Create const G4String amp placement const G4String amp modelName 0 where placement indicates which directory space the commands should occupy See for example G4TrajectoryDrawB yParticlelDFactory 2 12 5 View parameters View parameters such as camera parameters drawing styles wireframe surface etc are held by G4ViewParameters Each viewer holds a view parameters object which can be changed interactively and a default object for use in the vis viewer reset command If a toolkit developer of Geant4 wants to add entries of view parameters he should add fields and methods to G4ViewParameters 2 12 6 Visualisation Attributes All drawable objects should have a method const G4VisAttributes GetVisAttributes const A drawable object might be visible i e inheriting G4Visible such as a polyhedron polyline circle etc note that text is a slightly special case see below or asolid whose vis attributes are held in its logical volume 2 12 6 1 Finding the applicable vis attributes This is an issue for all scene handlers The scene handler is where the colour style auxiliary edge visibility marker size etc of individual drawable objects are needed
28. selection of visualisable objects interactive picking of graphical objects for attribute editing or feedback to the associated data highlighting incorrect intersections of physical volumes co working with graphical user interfaces Because it is very difficult to respond to all of these requirements with only one built in visualiser an abstract interface was developed which supports several complementary graphics systems Here the term graphics system means either an application running as a process independent of Geant4 or a graphics library to be compiled with Geant4 A concrete implementation of the interface is called a visualisation driver which can use a graphics library directly communicate with an independent process via pipe or socket or simply write an intermediate file for a separate viewer 2 12 2 The Graphics Interfaces G4VVisManager All user code writes to the graphics systems through this pure abstract interface It contains Draw methods for all the graphics primitives in the graphics reps category G4Polyline G4Circle etc geometry objects through their base classes G4VSolid G4PhysicalVolume and G4LogicalVolume and hits and trajectories through their base classes G4VHit and GAV Trajectory Since this 1s an abstract interface all user code must check that there exists a concrete instantiation of it A static method is provided so a typical user code fragment is G4VVisManager pVVisManager G4VVisManage
29. shared by all threads If performance is not a concern a simpler solution is available This is a simplified version of the split class mechanism that does not copy the initial status of the thread local data field from the master thread A typical example is a cache variable that reduces CPU usage storing in memory the value of a CPU intensive calculation for several events In such a case the G4Cache utility class can be employed see G4Cache 36 Design and Function of Geant4 Categories 2 14 3 3 Details on the split classes mechanism We describe here the split class mechanism central to Geant4 multi threading by developing a thread safe split class starting from our simplified example of G4Class It will be clear that this technique allows for minimal changes of the public API of the classes and thus is very suitable for making thread safe code without breaking backward compatibility To better describe the changes we introduce a setter and getter methods in the sequential version of our class e g before migration to multi threading class G4Class private G4double fValue public AGES f 4 void SetMyData G4double aValue fValue aValue G4double GetMyData const return fValue Instances of this class will be shared among threads because they are memory consuming objects and we want to transform this class into a split class As a first step we add to the declaration of fValue the TLS keyword G4T
30. the following 1 Ordering of GetPhysicalInteractionLength Inthe loop of GetPhysicalInteractionLength of AlongStepDolt the Transportation process has to be invoked at the end n the loop of GetPhysicalInteractionLength of AlongStepDolt the Multiple Scattering process has to be invoked just before the Transportation process 2 Ordering of Dolts There is only some special cases For example the Cherenkov process needs the energy loss information of the current step for its Dolt invocation Therefore the EnergyLoss process has to be invoked before the Cherenkov process This ordering is provided by the process manager Energy loss information necessary 10 Design and Function of Geant4 Categories for the Cherenkov process is passed using G4Step or the static dE dX table is used together with the step length information in G4Step to obtain the energy loss information Any other Status of this chapter Nov 1998 created by K Amako 10 06 02 partially re written by D H Wright 14 11 02 updated and partially re written by P Arce Dec 2006 Converted from latex to Docbook by K Amako 2 5 Physics Processes 2 5 1 Design Philosophy The processes category contains the implementations of particle transportation and physical interactions All physics process conform to the basic interface GAVP rocess but different approaches have been developed for the detailed design of each sub category For the decay sub category the
31. the majority of cases it is instance local These defintions are an over simplification that does not take into account pointers and sharing ownership of the pointee however the issues that we will discuss in the following can be extended to the case of pointers and the shared pointee It is clear that for the case of thread shared variables all threads need synchronization to avoid data race conditions it is worth recalling that there are no race conditions if the variable is accessed only to be read for example in the case that the variable is marked as const One or more instances of G4Class can exist at the same time in our application These instances can be thread local e g G4V Process or thread shared e g G4Logical Volume In addition the class data field fValue can be by itself thread local or thread shared The actions to be taken to transform the code depend on three key aspects Do we need to make the instance s of G4Class thread local or thread shared Do we need to make the data field fValue thread local or thread shared n case more than one instance of G4Class exits at the same time do we need fValue to be instance local or instance shared This gives rise to 8 different possible combinations summarized in the following figures each one discussed in detail in the following 34 Design and Function of Geant4 Categories thread shared data field thread local data field C probably nothing to do
32. 1 Y y 1 a G4SliceVector G4Proxyvector fslices t Tox 1 b 1 1 E 1 Fa Y 1 wi 1 d E x Q n ES 5 G4VoxelLimits G4int E i Excnig Loba T E y SAddLimit G4DrawVoxels clipToLimits vector HGetMaxExtent a rom STL std cetMinExtent createPlacedPolyhedra DrawVoxels setVoxelsVisAttributes Inside outcode GATransportationManager rom navigation igatorForTrad O orato Getrieldmanager 1 9 const GetNavigatorFo S const GetPropagatorl amp static GetTransporta packLevel 1 const GetDepth lt lt const gt gt GetTopReplica fHisto S const GetlopTransfo S const GetTopVolume S const GetTopVolumeT fNavigator fPropagatorInPield jneuLevel De GapropagatorinField S 1 from navigation 1 x h So fnormalNay LfvoxelNav computestep h 3 Ss fparamNa d lt lt const gt gt GetChordF 1 N e const GetDeltaln G4NormalNavigatidn M freplicaNav from navigation yl d s hn x ScomputeSafe G4ReplicaNavigation GavorelNayigation G4ParameterisedNavigation computestep from navigation from navigation from navigation LevelLocate const BackLocate S virtual Comp Sconputesafety ScomputeSafety d lt lt virtual gt gt Comp SConputeStep
33. 4HepRepFileSceneHandler ClearTransientStore 3 There is an option to accumulate trajectories across events and runs see commands vis scene endOfEventAction and vis Scene endOfRunAction 73 Extending Toolkit Functionality G4VSceneHandler ClearTransientStore This is typically called after an update and before drawing hits of the next event To simulate the clearing of transients hits etc the detector is redrawn if fpViewer fpViewer SetView fpViewer ClearView fpViewer DrawView ClearView rewinds the output file and DrawView re draws the detector etc For smart drivers DrawView is smart enough to know not to redraw the detector etc unless the view parameters have changed significantly see Section 3 7 1 3 3 7 1 7 More about scene models Scene models conform to the G4VModel abstract interface Available models are listed and described there in varying detail Section 3 7 1 5 describes their use in some common command actions In the design of a new model care should be taken to handle the possibility that the G4ModelingParameters pointer is zero Currently the only use of the modeling parameters is to communicate the culling policy Most models therefore have no need for modeling parameters 3 7 2 Enhanced Trajectory Drawing 3 7 2 1 Creating a new trajectory model New trajectory models must inherit from G4VTrajectoryModel and implement these pure virtual fu
34. 9 2 4 5 Ordering of Methods of Physics Processes ooocooccocccoccnnconnconnccnnccnnconnconcnnarcnccnnronose 10 2 5 PHYSICS PLOCESSES ie ordei De rn T 11 2 5 1 Design Philosophy ii terrere p gusta PREISE roe tla 11 2 522 Class Desi PMs societies Eme Rei ira ROI E EET bee pos 11 2 6 Hits and Digitization eet erre ipee esu E anges ayes sve eee ee ye eerie rers 12 2 6 1 Design Philosophy ig rrr Perrier E Ere Ern 12 2 6 2 Class DSI PMs iere Ie AI INPUNE rie IRePE 12 2 1 Geometry ie redet t P Pe UR ebore etie Pete Genes saab tete dienes Pies E esee nh 14 2 7 1 Design POSO A ao 14 2 1 2 Class DeSIgn ioseph D CDD ER EE EPRERS 14 2 7 3 Additional Geometry Diagrams sse e eere 16 2 8 Electroma netic Fields ss 503 iet rre ete Ese tee E PE ed rebat Up 17 2 9 VIDI ES 17 2 9 Design Philosophy cire nr ge terr REP ei PR Re EEEE aT ERR SERE ete sd 17 2 9 2 Class Design irte E IRIURE rs 17 2 10 Materials unirnos 19 2 10 1 Design Philosophy nie teen tede tr iT enean 19 2 10 2 Class Design cir eer D cosa ER REOR ERR REPE 20 2 11 Global Usage ut eene UL 20 2 11 1 Design Philosophy ctt rette Pre e Ra Re REEF RE ER RUPES 20 PAMEPENGEC ND TURN ERES 21 2 12 Vi1su lisation esco diofantica rain eR REPRE 25 2 121 Design Philosophy 1 tenis 25 2 122 The Graphics Interfaces cuicos tirar derrepente diia 25 2 12 3 The Geant4 Visualisation System sese Hee eer
35. Engine It is a singleton class which all the distribution classes derive from This singleton is instantiated by default RandFlat distribution class for flat random number generation It also provides methods to fill an array of flat random values given its size or shoot bits RandExponential distribution class defining exponential random number distribution given a mean It also provides a method to fill an array of flat random values given its size RandGauss distribution class defining Gauss random number distribution given a mean or specifying also a deviation It also provides a method to fill an array of flat random values given its size RandBreitWigner distribution class defining the Breit Wigner random number distribution It also provides a method to fill an array of flat random values given its size RandPoisson distribution class defining Poisson random number distribution given a mean It also provides a method to fill an array of flat random values given its size 21 Design and Function of Geant4 Categories RandEngine flat DRand48Engine flatArray RanluxEngine flat setSeed flat flatArray setSeeds flatArray setSeed 0 0 i sotSoedl setSeeds setSeeds 0 n 0 n HepJamesRandom 2 Y fiat 2 RanecuEngin flatArray i HepRandomEngine anecuEngine setSeed z flat m setSeeds at flatArray Prot is getSeedt e setSeeds getSeeds i 0 0 s
36. G4VUserPrimaryGeneratorAction G4UserRunAction G4UserSteppingAction and G4UserTrackingAction are not shared and a separate instance exists for each thread Since the master does not perform simulation of events user actions do not have functions for G4MTRunManager and should not be assigned to it G4RunAction is the exception to this rule since it can be attached to the master GIMTRunManager to allow for merging of partial results produced by workers 2 14 3 Memory handling in Geant4 Version 10 0 2 14 3 1 Introduction In Geant4 we distinguish two broad types of classes ones whose instances are separate for each thread such as a physics process which has a state and ones whose instances are shared between threads e g an element G4Element which holds constant data A few cases classes exist which have mixed behavior part of their state is constant and part is per worker A simple example of this is a particle definition such as G4Electron which holds both data which is constant and a pointer to the G4ProcessManager object for electrons which must be different for each worker thread We handle these split classes specially to enable data members and methods which correspond to the per thread state to give a different result on each worker thread The implementation of this requires an array for each worker thread and an additional indirection which imposes a cost each time the method is called However this overhead is smal
37. G4XXXSceneHandler G4XXXViewer Templates for the simplest possible graphics driver These would be suitable for an immediate driver i e one which renders each object immediately to a screen To do this simply instantiate and register for example visManager gt RegisterGraphicsSystem new G4XXX before visManager gt Initialise 68 Extending Toolkit Functionality Of course if the view needs re drawing as for example after a change of viewpoint the viewer requests a re issue of drawn objects e GAXXXFile G4XXXFileSceneHandler G4XXXFileViewer Templates for a file writing graphics driver The particular features are delayed opening of the file on receipt of the first item rewinding file on ClearView to simulate the clearing of views and prevent the duplication of material in the file closing of the file on ShowView which may also trigger the launch of a browser There are various degrees of sophistication in for example the allocation of filenames see FukuiRenderer or HepRepFil These templates also show the use of a specific AddSolid function whereby the specific parameters for example the dimensions of a G4Box can be accessed e GAXXXStored G4XXXStoredSceneHandler G4XXXStoredViewer Templates for a graphics driver with a store database The advantage of a store is that the view can be refreshed for example from a different viewpoint without a need to recompute It is up to the viewer to decide when a re compu
38. Geant4 User s Guide for Toolkit Developers Version geant4 10 1 Publication date 5 December 2014 Geant4 Collaboration Geant4 User s Guide for Toolkit Developers by Geant4 Collaboration Version geant4 10 1 Publication date 5 December 2014 Table of Contents T Introductio 5 rtr re e etre te Piece n t nib E Eee re Pide aeree E PO dM 1 1 1 Scope of this manual 5 iE ide 1 1 2 How to use this manual o iet erre D RI Penh Er RE ERR ERR RR sents ess eetoans 1 1 3 User Requirements Document o esise ieor aseeni norisi aeee A EEEE hem enm entes hen he mre rennen 1 2 Design and Function of Geant4 Categories ocoooccnoccnnccnnccnncnnnonnconnconncnnnconnconncrnnrnnnrnnnrnnrnnnrnnncnncinnicnn 2 A esri tere er sees ete eget e ves ee eere be ede ees e e pepe e EE SERM EE Pei Yeu 2 2 2 R n erret t ER ie Per RI RE e REI IE IIR PR 2 2 21 Design Philosophy ci 2 2 2 2 Class DESIGN sica e Stet to teer ette eR cbr mh kk Vd Tes t RUE 2 2 3 A n pene er ee e p pem eee Lie 5 2 3 1 Design Philosophy vrie ei pero th rr re SEE EEE EET ER SERRE RC HRP REPRE ME 5 2 3 2 Class DeSIBti 2 gr I EINEN ED E 5 DA T r acking tesis tec TEE ERREUR std 6 24 1 Design Philosophy eerte cree eere reete rye in Tope wees sea EUR IP e Eye iege 6 DAD Class Design ee epe te eret ERE Mea rt E TREES Ee RE eu eet ed 7 2 4 3 Tracking Algonthm vine ree 8 2 4 4 Interaction with Physics Processes ssssssessese eH eene
39. Geant4 currently handles magnetic and electric fields and in future releases will handle combined electromagnetic fields Fields due to other forces not yet included in Geant4 can be provided by describing the new field and the force it exerts on a particle passing through it For the time being all fields must be time independent This restriction may be lifted in the future In order to accommodate a new type of field two classes must be created a field type and a class that determines the force The Geant4 system must then be informed of the new field A new Field class A new type of Field class may be created by inheriting from G4Field class NewField public G4Field public void GetFieldValue const double Point 3 double pField 0 and deciding how many components your field will have and what each component represents For example three components are required to describe a vector field while only one component is required to describe a scalar field If you want your field to be a combination of different fields you must choose your convention for which field goes first which second etc For example to define an electromagnetic field we follow the convention that components 0 1 and 2 refer to the magnetic field and components 3 4 and 5 refer to the electric field By leaving the GetFieldValue method pure virtual you force those users who want to describe their field to create a class that implements it for their de
40. IZER and G4MUTEXINIT macros are used to initialize a mutex Use GIMUTEXLOCK and GAMUTEXUNLOCK functions to lock unlock a mutex The G4AutoLock class helps the locking unlocking of a mutex and should be always be used instead of GIMUTEXLOCK UNLOCK Example tinclude G4Threading hh include G4AutoLock hh Create a global mutex G4Mutex mutex G4MUTEX_INITIALIZER Alternatively call in the main function G4MUTEXINIT mutex A shared resource i e manipulated by all threads G4int aValue 1 G4ThreadFunReturnType myfunc G4ThreadFunArgType Explicit lock unlock G4MUTEXLOCK amp mutex taValue G4MUTEXUNLOCK amp mutex The following should be used instead of the previous because it guarantees automatic unlock of mutex When variable 1 goes out of scope G4MUTEXUNLOCK is automatically called G4AtuoLock 1 amp mutex aValue Explicit lock unlock Note that lock unlock is only tried if mutex is already locked unlock DOCK l lock No problem here aValue l unlock Jl TL exe Ge aValue return G4ThreadFunReturnType NULL A complete example of the usage of these functionalities is discussed in the unit test source global management test ThreadingTest cc Conditions are also available via the G4Condition type the G4CONDITION INITIALIZER macro and the two functions GACONDITION WAIT and G4CONDITIONBORADCAST The use of conditions allows the barrier mechanism e g synchronizati
41. Integrator lt T F gt Hermite T amp typeT F f G4int nHermite Wie Gauss Hermite method for integration of std exp x x f x from minus Infinity Lo plus infinity template class T class F gt G4double G4Integrator lt T F gt Jacobi T typeT F f G4double alpha G4double beta G4int nJacobi Gauss Jacobi method for integration of 1 x alpha 1 x beta f x 24 Design and Function of Geant4 Categories M neoni minus Umit Co Telus wake Sis HEPGeometry Documentation for the HEPGeometry module is provided in the CLHEP Reference Guide http cern ch clhep manual RefGuide or the CLHEP User Manual http cern ch clhep manual UserGuide Status of this chapter 01 12 02 minor update by G Cosmo 18 06 05 introductory paragraphs added and minor grammar changes by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 12 Visualisation 2 12 1 Design Philosophy The visualisation category consists of the classes required to display detector geometry particle trajectories tracking steps and hits It also provides visualisation drivers which are interfaces to external graphics systems A wide variety of user requirements went into the design of the visualisation category for example very quick response in surveying successive events high quality output for presentation and documentation flexible camera control for debugging detector geometry and physics
42. L gt gb ga 1 exp ga L In the occurence biasing two weights have to be taken into account When the track travels from 0 to without interaction it has a different probability to do so in the biased and analog schemes meaning that a weight for non interaction has to be applied this weight being e wyi 7 Pnral Puro GP If several processes are biased each with a dedicated law then as the total probability for non interaction is the product of individual probabilities the total non interaction weight is simply the product of the individual weights This non interaction weight has hence to be applied for all biased processes e Ifthe track then makes an interaction in the next segment d the analog process would have a probability gad to do so while this probability is y d t for the biased process A weight for interaction has hence to applied and is W oa go D where the analog and biased cross sections are for the process which is taking place 3 6 3 2 Implementation of Occurence Biasing Previous section shows that weights for non interaction probability and effective cross section are needed to compute the related non interaction and interaction weights The class G4VBiasingInteractionLaw is the interface for implementing interaction laws it defines the pure virtual methods virtual G4double ComputeNonInteractionProbabilityAt G4double length const 0 virtual G4double ComputeEffectiveCrossSecti
43. Physics Reference Manual 1 2 How to use this manual Part I to understand the goal of the software design of Geant4 it is useful to begin by reading the User Requirements Document referred to in the next section Part II Design and Function of the Geant4 Categories provides detailed information about the design of each class category and the classes in it Before considering an extension of one of the toolkit categories a detailed understanding of that category is required Part III Extending Toolkit Functionality explains in some detail how to extend the functionality of Geant4 Most of the class categories are covered and some which are especially useful to most users are covered in greater detail Itis not necessary to understand the entire manual before adding a new functionality To add a new physics process for example only the following items must be read and understood the design principle described in the Physics processes chapter of Part II techniques explained in the Physics processes chapter of Part III 1 3 User Requirements Document At the beginning of Geant4 development a set of user requirements was collected in order to inform the object oriented analysis and design of the toolkit The User Requirements Document follows the PSS 05 software engineering standards and is available at http cern ch geant4 00AandD URD pdf This document provides a general description of the main capabilities and c
44. Store a container for optionally storing created solids It enables traversal of all any solids by the UI user etc The class is a singleton G4VSolid position independent geometrical entities They have only shape and encompass both CSG and boundary representations They are optionally entered into the G4SolidStore This class defines but does not implement functions to compute distances to from the shape Functions are also defined to check whether a point is inside the shape to return the surface normal of the shape at a given point and to compute the extent of the shape G4V Touchable a class that maintains a reference on a given touchable element of the detector a kind of bookmark It enables a given detector element to be saved during tracking in case of booleans user code etc and the corresponding G4PhysicalVolume retrieved later with its state information path through the tree optionally restored so that navigation can be restarted G4Touchables provide fast access to the transformation from the global reference system to that of the saved detector element G4TouchableHistory object representing a touchable detector element and its history in the geomtrical hierarchy including its net resultant local gt global transform G4GRSSolid object representing a touchable solid It maintains the association between a solid and its net resultant local to global transform G4GRSVolume object representing a touchable det
45. Table 18 Design and Function of Geant4 Categories G4DynamicParticle G4ParticleDefinition G4DecayTable SelectADecayChannel GetDecayChannel index G4int G4DecayProducts G4DecayProductVector G4PhaseSpaceDecayChannel Figure 2 18 Decay Table Figure 2 19 Particle Decay Status of this chapter 27 06 05 section on design philosophy added from Geant4 general paper by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 10 Materials 2 10 1 Design Philosophy The design of the materials category reflects what exists in nature materials are made of a single element or a mixture of elements and elements are made of a single isotope or a mixture of isotopes Because the physical properties of materials can be described in a generic way by quantities which can be specified directly such as density or derived from the element composition only concrete classes are necessary in this category The material category implements the facilities necessary to describe the physical properties of materials for the simulation of particle matter interactions Characteristics like radiation and interaction length excitation energy 19 Design and Function of Geant4 Categories loss coefficients in the Bethe Bloch formula shell correction factors etc are computed from the element and if necessary the isotope composition The material category also implements faciliti
46. Thence the Draw method of the current trajectory model is invoked see Section 3 7 2 for details on trajectory models which in turn invokes Draw methods of the visualisation manager The resulting default sequence for a G4TrajectoriesModel is shown in Figure 3 11 DrawView ProcessView ProcessScene BeginModeling pModel gt DescribeYourselfTo this AddCompound trajectory trajectory DrawTrajectory DispatchToModel model Draw G4VisManager Draw gt BeginPrimitives objectTransform gt AddPrimitive EndPrimitives EndModeling Figure 3 11 The default sequence for a GAaPhysicalVolumeModel 3 7 1 6 Dealing with transient objects Any visualisable object not defined in the run duration part of a scene is treated as transient This includes trajectories hits or anything drawn by the user through the G4VVisManager user level interface unless as part of a run duration model implementation A flag fReadyForTransients is maintained by the scene handler In fact its normal state is t rue and only temporarily during handling of the run duration part of the scene is it set to false see description of ProcessScene Section 3 7 1 5 If the driver supports a graphical database it is smart to distinguish transient and permanent objects In this case every Add method of the scene handler must be transient aware In some
47. WIN32 threading model In the following the main functionalities available in the global management category are discussed 2 14 4 1 Types and functions related to the use of threads G4Thread defines the type for threads POSIX pthread t The types G4ThreadFunReturnType and G4ThreadFunArgType define respectively the return value and the argument type for a function executed in a thread Use G4THREADCREATE and G4THREADJOIN macros to respecively create and join a thread G4Pid t is the type for the PID of a thread Example include G4Threading hh Define a thread function using G4 types G4ThreadFunReturnType myfunc G4ThreadFunArgType val double value double val MESSAGE value is lt lt value return G4ThreadFunReturnType NULL I Example spawn 10 threads that execute myfunc int main int char MESSAGE Starting program int nthreads 10 G4Thread tid new G4Thread nthreads double valss new double nthreads 42 Design and Function of Geant4 Categories icone 4C aye Lar 0 po sube lt mamas p imanes JR di valss idx double idx G4THREADCREATE 8 tid idx myfunc amp valss idx ore Cabas LORTE 2dr A nthreads br CIC i 0 GATHREADJOIN tid idx MESSAGE Program ended return 0 2 14 4 2 Types and functions related to the use of mutexes and conditions G4Mutex is the type for mutexes in Geant4 POSIX pthread_mutex_t The GAMUTEX_INITIAL
48. allocated with more space for the new G4ClassData instances Since offset and workertotalspace are marked G4ThreadLocal this mechanism allows each thread to have its own copy of fValue The function foo can be called from different threads and they will use the thread shared a and b to access a thread local fValue data field No data race condition occurs and there is no need for mutexes and locks An additional complication is that if the initialization of the thread local part is not trivial and we want to copy some values from the corresponding values of the master thread in our example how is fValue to be initialized to a value that depends on the run condition The initial status of the thread local data field must be initialized for each worker in a controlled way The run cateogory classes must be modified to preapre the TLS space of each thread before any work is performed The following diagram shows the chain of calls in G4ParticleDefinition when a thread needs to access a process pointer shared static singleton gt thread local Figure 2 29 Simplified view of the split class mechanism 2 14 3 3 1 List of split classes In Geant4 Version 10 0 the following are split classes For geometry related split classes the class G4GeomSplitter implements the split class mechanism These are the geometry related split classes i G4LogicalVolume ii G4Physical Volume iii G4PVReplica iv G4Region
49. arentID and the process pointer which created this track are set The secondary track is added to the list of secondaries If it has O kinetic energy it is only added if it it invokes a rest process at the beginning of the tracking The track status is set according to what the process defined The method GaSteppingManager InvokeAtRestDolIts is called instead of the three above methods in case the track status is fStopAndALive It is on charge of selecting the rest process which has the shortest time before and then invoke it To select the process with shortest tiem the AtRestGPIL method of all active processes is called Each process returns an lifetime and the minimum one is chosen This method returm also a G4ForceCondition flag to indicate if the process is forced or not Forced Corresponding AtRestDolt is forced 2 NotForced Corresponding AtRestDolt is not forced unless this process limits the step Set the step length of current track and step to 0 Invoke the AtRestDolt methods of the specified at rest process and they return the ParticleChange The order of invocation of processes is inverse to the order used for the GPIL methods After it for each process the following is executed Set the current process as a process which defined this Step length Update the G4Step information by using final state information of the track given by a physics process This is done through the UpdateStepForAtRest method of the ParticleC
50. ase G4Cache is a template class that implements a light weight split classes mechanism Being a template it allows for storing any user defined type The public API of this class is very simple and it provides two methods T amp G4Cache lt T gt Get const void G4Cache T Put const T amp val const to access a thread local instance of the cached object For example include G4Cache hh class G4Class G4Cache lt G4double gt fValue void foo Store a thread local value G4double val someHeavyCalc fValue Put val void bar Get a thread local value G4double local fValue Get y Since Get returns a reference to the cached object is possible to avoid the use of Put to update the cache void G4Class bar Get a reference to the thread local value G4double amp local fValue Get Use local as in the original sequential code cache is updated without the need to use Put Jkoxee diro In case the cache holds an instance of an object it is possible to implement lazy initialization as in the following example include G4Cache hh class G4Class G4Cache lt G4Something gt fValue MOLI f Get a thread local value G4Something local fValue Get if local 0 I local new G4Something warning this may cause a memory leak Use of G4AutoDelete can help see later y Since the use of G4Cache implies some CPU penalty it is good practice to try to minimize its
51. ass G4VGraphicsScene is a minimal abstract interface of a 3D scene for the Geant4 kernel defined in the graphics reps category Since G4VSceneHandler and its concrete descendants inherit from G4VGraphicsScene the method DescribeYourselfTo can pass information of a 3D scene to a visualisation driver It is easy for a toolkit developer of Geant4 to add a new kind of visualisable component object It is done by implementing a new class inheriting from G4VModel G4VTrajectoryModel an abstract base class for trajectory drawing models A trajectory model governs how an individual trajectory is drawn Concrete models inheriting from G4VTrajectoryModel must implement two pure virtual functions virtual void Draw const G4VTrajectory amp G4int i mode 0 const 0 virtual void Print std ostream amp ostr const 0 See for example G4TrajectoryDrawByParticleID G4VModelFactory an abstract base class for factories creating models and associated messengers Itis not necessary to generate messengers for a trajectory model that will be constructed and configured directly in compiled code If the user requires model creation and configuration features through interactive commands however there must be a mechanism to generate both models and their associated messengers This is the role of G4VModelFactory Concrete factories inheriting from G4VModelFactory are responsible for creating a concrete model and concrete messengers To help ensure a type
52. ass head files or Software Reference Manual vis viewer clear viewer ClearView Clears buffer or rewinds file viewer FinishView Swaps buffer double buffer systems vis viewer flush vis viewer refresh vis viewer update vis viewer rebuild viewer SetNeedKernelVisit true vis viewer refresh If the view is auto refresh this command is also invoked after vis viewer create vis viewer rebuild or a change of view parameters vis viewer set etc viewer gt SetView Sets camera position etc viewer ClearView Clears buffer or rewinds file viewer DrawView Draws to screen or writes to file socket vis viewer update Us Extending Toolkit Functionality viewer ShowView Activates interactive windows or closes file and or triggers post processing vis scene notifyHandlers For each viewer of the current scene the equivalent of vis viewer refresh If flush is specified on the command line the equivalent of vis viewer update vis scene notifyHandlers is also invoked after a change of scene vis scene add etc 3 7 1 3 What happens in DrawView This depends on the viewer Those with their own graphical database for example OpenGL s display lists or Open Inventor s scene graph do not need to re traverse the scene unless there has been a significant change of view parameters For example a mere change of viewpoint requires onl
53. ation ProposeOccurenceBiasingOperation const G4Track track const G4BiasingProcessInterface callingProcess 0 The G4VBiasingOperation returned will have its ProvideOccurenceBiasingInteractionLaw called to get the biased interaction law to be used This method is called at the Post StepGetPhysicallnteractionLength level virtual G4VBiasingOperation ProposeFinalStateBiasingOperation const G4Track track const G4BiasingProcessInterface callingProcess 0 e The G4VBiasingOperation returned will have its ApplyFinalStateBiasing called to generated the physics based biased final state e This method is called at the Post StepDoIt level 3 6 3 Physics Process Occurence Biasing The occurence biasing is the biasing which affects the probability for a physics process to occur For now we discuss only the case of neutral particles ie having no continuous energy loss along a step The case of charged particles is expected to be treated in later releases The process occurence is driven by the exponential law which parameter in Geant4 is the process mean free path x Which is also the inverse of the cross section g The analog or natural probability density function pdf of interactions is given by Pa ca eXPC aft where is the distance at which the interaction occurs and where we have relabelled as ga In Geant4 volumes are made of a single material meaning that does not depend on at some po
54. ation is through registration 3 5 7 Level 5 Framework String De excitation G4ExcitedString GetPosition SetPosition Purely Abstract GetPartonList gt i et4Momentum G4VStringFragmentation ____ gt insertParton FragmentString TransformToCenterOfMass n AlignAlongZ sExcited GetHadron lt lt Concrete gt gt G4ExcitedStringDecay lt lt Purely Abstract gt gt _G4VFragmentationFunction GetLightConeZ lt lt Concrete gt gt lt lt Concrete gt gt G4QGSMFragmentation lt lt Concrete gt gt G4LundStringFragmentation GetLightConez G4FeynmanFragmentation amp GetLightConeZ geGetLiontconez Figure 3 8 Level 5 implementation framework of the hadronic category of Geant4 string fragmentation aspect The use case of this level is that of a user or theoretical physicist wishing to understand the systematic effects involved in combining various fragmentation functions with individual types of string fragmentation Note that this framework level is meeting the current state of the art making extensions and changes of interfaces in subsequent releases likely Requirements 1 Allow the selection of fragmentation function Design and interfaces A base class for fragmentation functions G4VFragmentation Function is provided It declares the GetLightConeZ interface 61 Extending Toolkit Functionality Framework functionality The design is a basic S
55. be the process defining the step the process NotCandidateForSelection this process cannot be the winner Even if its step length is taken as the smallest it will not be the process defining the step The method G4SteppingManager InvokeAlongStepDoIts is in charge of calling the AlongStepDolt methods of the different processes Ifthe current step is defined by a ExclusivelyForced PostStepGetPhysicalInteractionLength no AlongStepDolt method will be invoked Else all the active continuous processes will be invoked and they return the ParticleChange After it for each process the following is executed Update the G4Step information by using final state information of the track given by a physics process This is done through the UpdateStepForAlongStep method of the ParticleChange Then for each secondary t is checked if its kinetic energy is smaller than the energy threshold for the material In this case the particle is assigned a O kinetic energy and its energy is added as deposited energy of the parent track This check is only done if the flag ApplyCutFlag is set for the particle by default it is set to false for all particles user may change it in its G4VUserPhysicsList If the track has the flag IsGoodForTracking true this check will have no effect used mainly to track particles below threshold The parentID and the process pointer which created this track are set The secondary track is added to the list of secondari
56. before tracking the particle Clear secondary particle vector Pre tracking user intervention process Construct a trajectory if it is requested Give SteppingManager the pointer to the track which will be tracked Inform beginning of tracking to physics processes ON Ua bh uN ma Track the particle Step by Step while it is alive Call Stepping method of G4SteppingManager Append a trajectory point to the trajectory object if it is requested 7 Post tracking user intervention process 8 Destroy the trajectory if it was created Stepping in G4SteppingManager 1 Initialize current step 2 If particle is stopped get the minimum life time from all the at rest processes and invoke InvokeAtRestDoltProcs for the selected AtRest processes 3 If particle is not stopped Invoke DefinePhysicalStepLength that finds the minimum step length demanded by the active processes Invoke InvokeAlongStepDoltProcs Update current track properties by taking into account all changes by AlongStepDolt Update the safety Invoke PostStepDolt of the active discrete process Update the track length Send G4Step information to Hit Dig if the volume is sensitive 8 Design and Function of Geant4 Categories nvoke the user intervention process Return the value of the StepStatus 2 4 4 Interaction with Physics Processes The interaction of the tracking category with the physics processes is done in two ways First each process can limit
57. cases it is enough to open a graphical data base component in BeginPrimitives fill it in AddPrimitive and close it appropriately in EndPrimitives In others initialisation is done in BeginModeling and consolidation in EndModel ing see G40penGLStoredSceneHandler If any AddSolid method is implemented then the graphical data base component should be opened in PreAddSolid protecting against double opening for example void GAXXXStoredSceneHandler BeginPrimitives const G4Transform3D amp objectTransformation G4VSceneHandler BeginPrimitives objectTransformation If thread of control has already passed through PreAddSolid avoid opening a graphical data base component again if fProcessingSolid for other solids The reason for this distinction is that at end of run the user typically wants to display trajectories on a view of the detector then at the end of the next event 3 erase the old and see new trajectories The visualisation manager messages the scene handler with ClearTransientStore just before drawing the trajectories to achieve this If the driver does not have a graphical database or does not distinguish between transient and persistent objects it must emulate ClearTransientStore Typically it must erase everything including the detector and re draw the detector and other run duration objects ready for the transients to be added File writing drivers must rewind the output file Typically void G
58. cene scene AddSolid this sceneHandler PostAddSolid The scene handler may implement the virtual function AddSolid const G4Box amp or inherit void G4VSceneHandler AddSolid const G4Box8 box RequestPrimitives box RequestPrimitives converts the solid into primitives G4Polyhedron and invokes AddPrimitive BeginPrimitives fpObjectTransformation pPolyhedron solid GetPolyhedron AddPrimitive pPolyhedron gt EndPrimitives The resulting default sequence for a G4PhysicalVolumeModel is shown in Figure 3 10 Extending Toolkit Functionality DrawView ProcessView ProcessScene BeginModeling pModel gt DescribeYourselfTo this pSol DescribeYourselfTo sceneHandler gt sceneHandler AddSolid this gt RequestPrimitives solid gt AddPrimitive pPolyhedron EndPrimitives sceneHandler PostAddSolid EndModeling Figure 3 10 The default sequence for a G4PhysicalVolumeModel Note the sequence of calls at the core SceneHandler PreAddSolid theAT pVisAttribs pSol DescribeYourselfTo sceneHandler gt sceneHandler AddSolid this gt RequestPrimitives solid gt BeginPrimitives fpObjectTransformation gt pPolyhedron solid GetPolyhedron gt AddPrimitive pPolyhedron EndPrimitives sceneHandler PostAddSolid is reduced to SceneHandler PreAddSolid theAT
59. cle G4int Z 63 Extending Toolkit Functionality which sets the Z range of the element based data set G4bool IsIsoApplicable const G4DynamicParticle G4int G4int A which sets the Z and A range of the isotope based data set and SetMinKinEnergy G4double SetMaxKinEnergy G4double GetMinKinEnergy and GetMaxKinEnergy for defining the applicable energy range of the data set 3 5 8 3 Developing a new hadronic process As mentioned above it is preferable to add new physics in terms of a model and assign the model to an existing process rather than develop a new specific process Under certain circumstances though a directly implemented process may be necessary In that case 1t must derive from G4HadronicProcess and three methods of that class must be implemented virtual G4VParticleChange PostStepDolt const G4Track amp const G4Steps virtual G4bool IsApplicable const G4ParticleDefinition amp and G4double GetMeanFreePath const G4Track amp aTrack G4double G4ForceCondition PostStepDolt is responsible for generating the final state of an interaction given the track and step information It must update the state of the track flagging it as Alive StopButAlive StopAndKill KillTrackAndSecondaries Suspend or PostponeToNextEvent It is roughly analagous to the ApplyYourself method in models IsApplicable serves the same purpose in processes as it does in models GetMeanFreePath
60. const G4ThreeVector amp p Calculate distance to nearest surface of shape from an outside point p The distance can be an underestimate G4double DistanceToIn const G4ThreeVector amp p const G4ThreeVector amp v Return the distance along the normalised vector v to the shape from the point at offset p If there is no intersection return kInfinity The first intersection resulting from leaving a surface volume is discarded Hence this is tolerant of points on surface of shape G4double DistanceToOut const G4ThreeVector amp p Calculate distance to nearest surface of shape from an inside point The distance can be an underestimate G4double DistanceToOut const G4ThreeVector amp p const G4ThreeVector amp v const G4bool calcNorm false G4bool validNorm 0 G4ThreeVector n 0 Return distance along the normalised vector v to the shape from a point at an offset p inside or on the surface of the shape Intersections with surfaces when the point is not greater than kCarTolerance 2 from a surface must be ignored If calcNorm is true then it must also set validNorm to either true if the solid lies entirely behind or on the exiting surface Then it must set n to the outwards normal vector the Magnitude of the vector is not defined false if the solid does not lie entirely behind or on the exiting surface If calcNorm is false then validNorm and n are unused G4bool CalculateExtent const EAxis pAxis const G4VoxelLim
61. created in the ConstructParticles method of your physics list New properties may be added if necessary G4Monopole has a a property for magnetic charge Values of properties need to be given in the static method as other particle classes G4Monopole G4Monopole MonopoleDefinition G4double mass G4int mCharge G4int eCharge if theMonopole theMonopole new G4Monopole monopole mass 0 0 MeV OF O 0 0 0 0 0 MOS Oni OF OF 0 true Aog Op return theMonopole 3 3 3 Nuclide properties from Evaluated Nuclear Structure Data File G4NuclideTable G4NuclideTable was introduced in Geant4 V10 to provide properties of nuclide states The excitation energy and decay times of each state are listed in this table The spin and dipole magnetic moment are also given for some states The source of the data in this table is ENSDF of August 2012 24 359 states were extracted from the source and ground states and excited states having half lives longer than 1 nanosecond were implemented in the source code of the class The total number of hard coded states 6807 is sufficient for most use cases and so G4NuclideTable uses these by default The full set of 24 359 states is contained in a data file G4NuclideTable accesses the data file pointed to by the environment variable G4ENSDFSTATEDATA To get very fine position and time information about level transitions of nuclides users may want to transport very short lived excited s
62. ctorManager a list of G4SensitiveDetectors G4HitsStructure a tree like structure of G4Hit collections Each branch represents the hits in given sub detector For example the first level of branches may consist of a tracker ECAL and HCAL while the second level in HCAL consists of the barrel and endcaps Finally the barrel may have phi slices Z slices etc G4VSensitiveDetector an abstract class of all of sensitive volumes G4HitsCollection a collection of hits Instantiates an RWCollection class G4VHit this class has all the information about a particular hit caused by a single step G4VDigitizer the class of objects which transform the hits deposited by particles into digitizations 12 Design and Function of Geant4 Categories G4DigitizerManager the single object dispatching common messages to individual digitizers G4VDigi an abstract base class for all G4 digitizations This could be data as simple as a singe byte or as complex as an Ntuple G4DigiStructure digitizations are organized as a structure which could be anything between a single value and an Ntuple The object oriented design of the hit related classes is shown in the following class diagrams The diagrams are described in the Booch notation Figure 2 8 shows the general management of hit classes Figure 2 9 shows the OO design of user related hit classes Figure 2 10 shows the OO design of the readout geometry G4SDManager
63. d Trajectory Drawing added by Jane Tinsley 03 12 05 Creating a new visualisation driver from Part IT by John Allison 09 01 06 Creating a new visualisation driver considerably expanded by John Allison 20 06 06 Some sections improved or added from draft vis paper John Allison Dec 2006 Conversion from latex to Docbook verson by K Amako 76 Bibliography Gamma1995 E Gamma Design Patterns Addison Wesley Professional Computing Series 1995 QGSM Kaidalov A B Ter Martirosyan Phys Lett B117 1982 247 ENDFForm Data Formats and Procedures for the Evaluated Nuclear Data File National Nuclear Data Center Brookhaven National Laboratory Upton NY USA QMD For example VUU and R QMD model of high energy heavy ion collisions H Stocker et al Nucl Phys A538 53c 64c 1992 CHIPS P V Degtyarenko M V Kossov H P Wellisch Eur Phys J A 8 217 222 2000 VNI Klaus Geiger Comput Phys Commun 104 70 160 1997 Brookhaven BNL 63762 PYTHIA7 Pythia version 7 0 0 a proof of concept version M Bertini L Lonnblad T Sjorstrand LU TP 00 23 hep ph 0006152 May 2000 77
64. d by G4RunManager Design and Function of Geant4 Categories User Initializations G4VUserPhysicsList G4VUserDetectorConstruction G4VUserActionlnitialization G4MTRunManager G4WorkerRunManager L G4UserWorkerlnitialization V User Actions G4VUserPrimaryGeneratorAction G4UserRunAction G4UserSteppingAction G4UserTrackingAction G4UserStackingAction Figure 2 1 Class diagram for main run category classes For a descriptiont of multi threading functionality refer to Parallelism in Geant4 multi threading capabilities chapter One of the main functions of the run category is to control the life cycle of a Geant4 application again with reference to the case of a multi threaded application the following schema describes it Design and Function of Geant4 Categories Application 1 G4MTRunManager 2 BeamOn 2 1 SetupGeometryAndPhysics 2 G4WorkerRunManager 2 3 BeamOn 2 3 1 SimulateEvent 2 3 3 EndOfRun 2 3 4 3 Terminate Figure 2 2 Life cycle of a Geant4 application and main run category classes A list of the main classes for the category is provided G4Run This class represents a run An object of this class is constructed and deleted by G4RunManager G4RunManager the run controller class Users must register detector construction p
65. d that the user become familiar with the Geant4 hadronic framework This is covered in detail in the chapter on Extended Functionality in this manual The framework uses the object oriented principles of abstraction and re use to provide a number of services to the developer The part of the framework used will depend on the type of model For example high energy models can take advantage of already developed string excitation and decay functions and medium energy models can use the intra nuclear propagation base class and the nuclear de excitation handler Writing the IsApplicable method The is a straightforward but important method Most models are quite specific in their range of use and the developer must codify this It is recommended that this method test for ranges of projectile energy particle type and target atomic number and weight and return false when these ranges are exceeded 3 5 8 2 Developing a new cross section set New cross section sets should derive from G4VCrossSectionDataSet This class serves as a container of cross section data and provides a number of access methods that must be implemented by the developer The essential methods are G4double GetElementCrossSection const G4DynamicParticle G4int Z which retrieves element based cross sections G4double GetIsoCrossSection const G4DynamicParticle G4int Z G4int A which retrieves isotope based cross sections G4bool IsElementApplicable const G4DynamicParti
66. e 26 212 4 Modeling Subscategory zer o x rer EE UR EY ERE EE RR EXE PREX RE RE ERE RARE A 27 2 12 5 PS nei I IUe Ert oes MOEN MEE CUu KTERE IOT sae 28 2 12 6 Visualisation Attributes piison nre ee tert tse bere te rrde psc 28 23s Intercoms ME C EON 30 2 13312 Design Philosophy one DP RR REPRE REIR REPE TEOS 30 2 13 2 Class DESTA 30 2 14 Parallelism in Geant4 multi threading capabilities esse 31 2 14 1 Event level parallelis cette Rr roue des 31 2 14 2 General Design o Lio ho PD IEEE EESE EEES REER SPES EEE DIERE SEP 32 2 14 3 Memory handling in Geant4 Version 10 0 sssessseee HH 33 2 14 4 Threading model utilities and functions ocooccoccocnncnoconcnoroncnoroncnnconcnnroncnnroncnnrononns 42 2 14 5 Additional material coin erre tenete ertet ette e EE Dese te sve eins 43 3 Extending Toolkit Functionality ise eie tttm cn e erae TERRE ROSTE EE EE Sepe 45 111 Geant4 User s Guide for Toolkit Developers 3l Geometry P 45 3 1010 What c n b e extended Piti ii aee tede a d A acess 45 3 12 Adding anew type of Sold ette e eter us Ce nte cidad nee SER EE See HERI 45 3 1 3 Modifying the Navigator oer e rtp peter eer Tee rude Poe de e Ud 48 3 2 Electromagnetic Fields rre yesh veh ote Petro Eee re eese ee eoe pe oed eee Poe ie e eR ese ee 49 32 1 Creatine a New Type of Field i oo o ve eR o oet de dea E Hu t 49 3 3 Particies qe CILE 51
67. e cross sections and final state generation The frameworks are then refined for increasingly specific use cases building a hierarchy in which each level implements the interface specified by the level above it A given hadronic process may be implemented at any one of these levels For example the process may be implemented by one of several models and each of the models may in turn be implemented by several sub models at the lower framework levels 2 5 2 Class Design 2 5 2 1 General The object oriented design of the generic physics process G4VProcess and its relation to the process manager is shown in Figure 2 6 Figure 2 7 shows how specific physics processes are related to G4V Process Design and Function of Geant4 Categories currentParticle G4ParticleDefiniti G4ProcessTableMessenger G4ProcessManager GetAtRestProcessVector GetAlongStepProcessVector GetPostStepProcessVector AddProcess GetProcessOrdering GetParticleType p GetAttribute G4ProcessVector 4 G4ProcessManagerMessenger G4ProcessAttrVector Figure 2 6 Management of Physics Processes dol GiVParticleChange G4ProcessManagermessenger jeManagor G4ProcessManager y J oapariciecnange PA UrdaleStepForktRest UpdaleStepForAlonoStepo rPostStep ECL CA gt rProcessMananervassenger 1 caParticiechangoFertransport pPatileCha
68. e system in a seamless manner Requirements 1 Provide a standard interface to be used by process implementations 2 Provide registration mechanisms for processes 1 The same can be achieved with template specialisations with slightly improved CPU performance but at the cost of significantly more complex designs and with present compilers significantly reduced portability 54 Extending Toolkit Functionality Design and interfaces Both requirements are implemented in a sub set of the tracking physics interface in Geant4 The class diagram is shown in Figure 3 1 Purely Abstract G4VProcess PostStepGetPhysicallnteractionLength PostStepDolt alongStepGetPhysicalinteractionLength AlongStepDolt atRestGetPhysicallnteractionLength atRestDolt Abstract G4VDiscreteProcess vee SPostStepGetPhysicallnteractionLength PostStepDolti sto AtRestGetPhysicallnteractionLength AtRestDolt lt lt Abstract gt gt G4HadronicProcess P lt cvirtual gt gt GetMicroscopicCrossSection lt cvirtual gt gt PostStepDolt S RegisterMe hooseHadronicinteraction GeneralPostStepDolt lt lt static gt gt GetlsotopeProductionInfo S RegisterlsotopeProductionModel lt lt static gt gt EnablelsotopeProductionGlobally S static DisablelsotopeProductionGlobally EnablelsotopeCounting DisablelsotopeCounting Figure 3 1 Level 1 implementation framework o
69. ector element It maintains associations between a physical volume and its net resultant local to global transform G4AffineTransform a class for geometric affine transformations It supports efficient arbitrary rotation and transformation of vectors and the computation of compound and inverse transformations A rotation flag is maintained internally for greater computational efficiency for transforms that do not involve rotation G4UserLimits responsible for user limits on step size ascribable to individual volumes Figure 2 11 shows a general overview in UML notation of the geometry design A detailed collection of class diagrams from the geometry category is found in the Appendix Design and Function of Geant4 Categories G4Solidstore e GiNavigator de lt static gt gt Demegister ic GetInstance from navigation de lt static gt gt GetInstance Sopenceonetry G PhysicalVolumeStore ccstatic gt gt Register ppuildoptimisations virtual Computestep y amp c lt static gt gt DeRegister qb lt cconst gt gt GetCurrentLoc const GetGlobalToLo lt lt const gt gt GetLocalToGlo lt lt const gt gt GetWorldVolume d lt lt virtual gt gt Resethierarch setGeonetricallyLimitedst setiorldVolume M A amp lt atatie gt gt GetInstance 4 S amp lt static gt gt Register Mecstaticv De j GAPhysicalvolumeLis
70. ed when the Geant4 state indicates the end of event has been reached The scene has an extent G4VisExtent which is updated by the scene when a new model is added each model itself has an extent and a standard target point these are used to define the standard view see below In addition the scene keeps flags which indicate whether end of event objects should be accumulated or refreshed for each event or run G4VGraphicsSystem This is an abstract base class for scene handler and viewer factories It is used by the visualisation manager to create scene handlers and viewers on request G4VSceneHandler A sub class of G4VGraphicsScene itself an abstract base class for specific scene handlers whose job is to convert the scene into graphics system specific code for the viewer For example the scene handler may create a graphical database taking care to separate run duration persistent and end of event transient information this is described further in Section 3 7 1 6 e G4V Viewer An abstract base class for specific viewers Its job is to create windows or files and identify where and how the final view should be rendered It has view parameters G4ViewParameters which specify viewpoint direction type of rendering wireframe or surface etc It is the view s responsibility noting the scene s extent and target point to choose a camera position and magnification that ensures that the scene is automatically and comfortably rendered i
71. egrate all functionalities required for the propagation of a particle into a single class This design approach looks object oriented because a particle in the real world propagates by itself while interacting with the material surrounding it However in terms of data hiding which is one of the most important ingredients in the object oriented approach the design can be improved Combining all the necessary functionalities into a single class exposes all the data attributes to a large number of methods in the class This is basically equivalent to using a common block in Fortran Instead of the big class approach a hierarchical design was employed by Geant4 The hierarchical approach which includes inheritance and aggregation enables large complex software systems to be designed in a structured way The simulation of a particle passing through matter is a complex task involving particles detector geometry physics interactions and hits in the detector It is well suited to the hierarchical approach The hierarchical design manages the complexity of the tracking category by separating the system into layers Each layer may then be designed independently of the others In order to maintain high performance tracking use of the inheritance 1s a relation hierarchy in the tracking category was avoided as much as possible For example t rack and particle classes might have been designed so that a track is a particle In this scheme however when
72. end the final state particles to the process by filling G4HadFinalState and setting its status Step 4 is accomplished by using the various Get and Set methods provided by the class G4HadFinalState The developer must also decide whether the original projectile survives the interaction disappears or is suspended This is done with the SetStatusChange method If the projectile survives the change in its energy and momentum must be set with the provided methods and it must be flagged as isAlive If the particle disappears it must be flagged as stopAndKill Geant4 provides a large number of Lorentz transformation tools which may be used to complete steps 1 and 3 How step 2 is accomplished is entirely up to the developer This could be as simple as a look up table which assigns a final state to an initial state or as complex as a theoretical high energy generator Typically the user will have to provide methods of sampling final state multiplicities energies and angles using random number generators provided by Geant4 For example the cosine of the polar angle of an isotropic angular distribution could be sampled as follows G4double cosTheta 2 G4UniformRandom 1 The developer must also see to it that the model conserves energy and momentum Currently the hadronic framework checks that final states do not exceed reasonably small limits of non conservation Using the hadronic framework For complex models it is recommende
73. enerators and of specific solutions for storing the Monte Carlo truth G4Event avoids keeping any transient information which is not meaningful after event processing is complete Thus the user can store objects of this class for processing further down the program chain For performance reasons G4Event and its content classes are not persistent Instead the user must provide the transient to persistent conversion 2 3 2 Class Design G4Event This class represents an event It is constructed and deleted by G4RunManager or its derived class G4EventManager This class controls an event It must be a singleton and should be constructed by G4RunManager G4VPrimaryGenerator the abstract base class of all of primary generators This class has only one pure virtual method GeneratePrimary Vertex which takes a G4Event object generates a primary vertex and associates primary particles with the vertex Booch diagrams for classes related to the event and event generator classes are shown in Figure 2 3 and Figure 2 4 1 doBeDrawni toBeStorad trajectory GaUserTrsjectory ES GaDynamicPartice GATrajectoy from ParicleDetiniton Fie usors asal g N 0830 m l Thu Aug 31 14 00 49 1995 Class Diagram EventManagement Main Figure 2 3 Event Design and Function of Geant4 Categories G4EventGenerator addGenerator generateOneEvent gimmeVertex G4OrderedV ector E from BaseClass v e
74. er Chapter Section 2 12 on Visualisation object oriented design in Part II Many of the concepts used here are defined there and it strongly recommended that a writer of a new visualisation 67 Extending Toolkit Functionality driver or trajectory drawer reads Chapter Section 2 12 first The class structure described there is summarised in Figure 3 9 G4VVismanager G4VGraphicsScene Graphics Interface G4VisManager G4VGraphicsSystem G4VSceneHandler G4VViewer G4VisExecutive GAXXX G4XXXSceneHandler GAXXXViewer Geant4 Visualisation System G4Scene G4ViewParameters Figure 3 9 Geant Visualisation System Class Diagram 3 7 1 Creating a new graphics driver To create a new graphics driver for Geant4 it is necessary to implement a new set of three classes derived from the three base classes G4VGraphicsSystem G4VSceneHandler and G4VViewer 3 7 1 1 A useful place to start A skeleton set of classes is included in the code distribution in the visualisation category under subdirectory visualisation XXX but they are not default registered graphics systems There are several sets of classes described in more detail below A recommended approach is to copy the files that best match your graphics system to a new subdirectory with a name that suits your graphics system Then 1 Change the name of the files change the code XXX or XXXFi le etc as chosen to somethin
75. erit from G4SmartFilter which implements some specialisations on top of G4VFilter The models implement these pure virtual functions Evaluate method implemented in subclass virtual G4bool Evaluate const T amp 0 Print subclass configuration virtual void Print std ostream amp ostr const 0 To use the new filter model directly in compiled code simply register it with the G4VisManager eg 75 Extending Toolkit Functionality G4VisManager visManager new G4VisExecutive visManager gt Initialise Create custom model MyCustomTrajectoryFilterModel myModel new MyCustomTrajectoryFilterModel custom Configure it if necessary then register with G4VisManager visManager gt RegisterModel myModel 3 7 3 2 Adding interactive functionality Additional classes need to be written if the new model is to be created and configured interactively The mechanism is exactly the same as that used to create enchanced trajectory drawing models and associated messengers See the filter factories in G4TrajectoryFilterFactories for example implementations 3 7 4 Other Resources The following sections contain various information for extending other class functionalities of Geant4 visualisation User s Guide for Application Developers Chapter 8 Visualization User s Guide for Toolkit Developers Object oriented Analysis and Design of Geant4 Classes Section 2 12 Status of this chapter 03 12 05 Enhance
76. ers own thread private instances of the other classes e g SensitiveDetectors hits etc This choice allowed the design of a lock free code i e no use of mutex during the event loop which guarantees maximum scalability cfr Euro Par2010 Part II LNCS6272 pp 287 303 Thread safety is obtained via Thread Local Storage Similar to the sequential version of Geant4 master and workers are represented by instances of classes inheriting from G4RunManager the G4MTRunManager class represents the master model while G4WorkerRunManager instances represent worker models The user is responsible for instantiating a single G4MTRunManager or derived user class instance This class will instantiatiate and control one 32 Design and Function of Geant4 Categories or more G4WorkerRunManager instances Users should never instantiate directly an instance of the G4WorkerRunMAnager class A simplified class diagram of the relevant classes for multi threading and their relationship is shown here Figure 2 27 Relevant classes and their interaction for multi threaded applications As in sequential Geant4 users interact with the Geant4 kernel via user initializations and user actions User initializations G4VUserDetectorConstruction GVUserPhysicsList and the new G4VUserActionInitializtion instances are shared among all threads as such they are registered to the G4MTRunManager instance while user actions
77. es If it has O kinetic energy it is only added if it it invokes a rest process at the beginning of the tracking The track status is set according to what the process defined The method G4SteppingManager InvokePostStepDolts is on charge of calling the PostStepDolt methods of the different processes Invoke the PostStepDolt methods of the specified discrete process the one selected by the PostStepGetPhysicalInteractionLength and they return the ParticleChange The order of invocation of processes is inverse to the order used for the GPIL methods After it for each process the following is executed Update PostStepPoint of Step according to ParticleChange Update G4Track according to ParticleChange after each PostStepDolt Update safety after each invocation of PostStepDolts The secondaries from ParticleChange are stored to SecondaryL ist 9 Design and Function of Geant4 Categories Then for each secondary t is checked if its kinetic energy is smaller than the energy threshold for the material In this case the particle is assigned a O kinetic energy and its energy is added as deposited energy of the parent track This check is only done if the flag ApplyCutFlag is set for the particle by default it is set to false for all particles user may change it in its G4VUserPhysicsList If the track has the flag IsGoodForTracking true this check will have no effect used mainly to track particles below threshold The p
78. es to describe surface properties used in the tracking of optical photons 2 10 2 Class Design The object oriented design of the materials related classes is shown in the class diagram Figure 2 20 The diagram is described in the Booch notation RWTPtrOr deredVect rom RWTools Y Y A i G4Element G4lsotope GtMatoria Te Table 1 1 o Um 2 8 a E 1 1 1 1 1 theMaterialTable theElementTable thelsotope n E e 1 n 158 i a G4Material G4Element En e cemento Addisotope DumpTsbi umga e0 Blimp set E le 1 e n K n theElements 1 thelsotopes 1 1 e G4Element G4lsotope Vector Vector 0 1 Qn RWTPtrVe ctor from RWTools Figure 2 20 Status of this chapter 27 06 05 section on design philosophy add from Geant4 general paper by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 11 Global Usage 2 11 1 Design Philosophy The global category covers the system of units constants numerics and random number handling It can be considered a place holder for general purpose classes used by all categories defined in Geant4 No back dependencies to other Geant4 categories affect the global domain There are direct dependencies of the global category on external packages such as CLHEP STL and miscellaneous system utilities Within the management sub category are utility classes generally used within the Geant4 kernel They are for the most part uncorrelated with one another a
79. etSeed setSeeds 1 0 A f theEngine 0 HepRandom flat flatArray getTheEngine getTheGenerator getTheSeed getTheSeeds getTheTableSeeds setTheEngine setTheSeed setTheSeeds gt 1 Y RandFlat L3 fi Piu A RandPoisson fre fire shoot shoot shootArray shootArray shootint fireArray 0 n 0 n RandGauss RandExponential nd RandBreitWigner iet shootArray fire e fireArray shoot i shootArray 0 n shootArray fireArray tireAmay 0 0 n Figure 2 21 HEPRandom module Figure 2 22 is a dynamic object diagram illustrating the situation when a single random number is thrown by the static generator according to one of the available distributions Only one engine is assumed to active at a time Just one of the following mando Engines at a time is active i i HepJamesRandom default HepRandomEngine DRand48Engine RandEngine RanluxEngine RanecuEngine je 2 setSeed long int Y 1 setTheEngine f v theEngine RandGauss b Thu theGenerator 7 flat k 10 fat RandBreit G ue is fat 17 shoot Wigner 3 flat tart yE 5 shoot a aGenerator 16 flat G HepRandom G asta sto og P G RandPoisson vw 8 shoot 48 14 shoot 12 flat 9 flat a RandExpon ential 11 shoot RandFlat Figure 2 22 Shooting via the generator Figure 2 23 illustrates a random number bei
80. ever a t rack object is used time is spent copying the data from the particle object into the track object Adopting the aggregation has a relation hierarchy requires only pointers to be copied thus providing a performance advantage Design and Function of Geant4 Categories 2 4 2 Class Design Figure 2 5 shows a general overview of the tracking design in Unified Modelling Language Notation G4TrackingManager G4Trajectory 0 1 1 GetTrack G4UserTrackingAction GATraiectoryPoint com GimmeTrajectory feTrackingManager dal Ns paraa GimmeSecondaries TT PreUserTrackingActionO PrawTrajectory fpTrajectory ProcessOneTrackO 1 foUserTrackingActicg 1 postUserTrackingActionO 0 AppendStep EventAborted Verbose trackingManager G4SelectedAlongStepDoltVector li 0 1 1 fpSteppingManager G4TrackingMessenger fSelectedAlongStepDoltVector 0 1 Y 1 1 G4SteppingManager GetTrack 0 1 GetStep steppingManager Stepping SetinitialStepQ 1 DefinePhysicalStepLengthO fSelectedAtRestDoltVector InvokeAtRestDoltProcs InvokeAlongStepDoltProcs 0 1 InvokePostStepDoltProcs 1 p CalculateSafety 0 1 G4SelectedAtRestDoltVector 01 Secondary t i 0 1 GATrackVector 3 fManager fpSteppingManager 0 1 fSecondary fSelectedPostStepDoltVector 04 G4SelectedPostStepDoltVector N LLL fUserSteppingAction 011 fVerbose 011 1 A G4UserSteppingActi serSteppingAction G4SteppingVerbose
81. f the hadronic category of GEANT4 All processes have a common base class G4VP rocess from which a set of specialised classes are derived Three of them are used as base classes for hadronic processes for particles at rest G4VRestProcess for interactions in flight GAVDiscreteProcess and for processes like radioactive decay where the same implementation can represent both these extreme cases GAVRestDiscrete Process Each of these classes declares two types of methods one for calculating the time to interaction or the physical interaction length allowing tracking to request the information necessary to decide on the process responsible for final state production and one to compute the final state These are pure virtual methods and have to be implemented in each individual derived class as enforced by the compiler Framework functionality The functionality provided is through the use of process base class pointers in the tracking physics interface and the G4Process Manager All functionality is implemented in abstract and registration of derived process classes with the GAProcess Manager of an individual particle allows for arbitrary combination of both Geant4 provided processes and user implemented processes This registration mechanism is a modification on a Chain of Responsibility It is outside the scope of the current paper and its description is available from G4Manual 3 5 4 Level 2 Framework Cross Sections and Models At t
82. g acting on the process PostStepDoIt Biasing of non physics type Where by that we mean biasing actions which act on particles but are not modifying a physics process behavior Splitting and killing are the important example of such cases 3 6 2 Design of Generic Biasing We have decided to split the actual biasing actions change probability occurence of a process change its final state generation split kill etc from the decisions about these actions to be taken The reason for this is that several biasing actions are often needed to build one biasing technique these actions having to be selected along some specific logic of the technique For example a technique like the force collision of MCNP involves a splitting a force interaction of one copy in the volume and a force free flight under zero weight of the other copy in the volume The classes which provides the interfaces for these biasing actions and decisions are respectively e G4VBiasingOperation G4VBiasingOperator A third class G4BiasingProcessInterface provides the interface between these classes and the stepping 3 6 2 1 The G4VBiasingOperation Interface Class G4VBiasingOperation defines two types of methods methods for physics based biasing virtual const G4VBiasingInteractionLaw ProvideOccurenceBiasingInteractionLaw const G4BiasingProcessInterface callingProcess G4ForceCondition amp proposeForceCondition 0 which
83. g that suits your graphics system Change XXX similarly in all files Change XXX similarly in name G4XXX in GNUmakefile Add your new subdirectory to SUBDIRS and SUBLIBS in visualisation GNUmakefile Look at the code and use it to build your visualisation driver You might also find it useful to look at ASCIITree and VTree as an example of a minimal graphics driver Look at FukuiRenderer as an example of a driver which implements AddSolid methods for some solids Look at OpenGL as an example of a driver which implements a graphical database display lists and the machinery to decide when to rebuild OpenGL is complicated by the proliferation of combinations of the use or not of display lists for three window systems X windows X with motif interactive Microsoft Windows Win32 a total of six combinations and much use is made of inheritance to avoid code duplication NA 6 If it requires external libraries introduce two new environment variables GAVIS BUILD XXX DRIVER and G4VIS_USE_XXX where XXX is your choice as above and make the modifications to e source visualization management include G4VisExecutive icc e config GAVIS BUILD gmk config G4VIS_USE gmk 3 7 1 1 1 Graphics driver templates in the xxx sub category You may use the following templates to help you get started writing a graphics driver The word template is used in the ordinary sense of the word they are not C templates e GAXXX
84. gn of the physics process classes including the addition or subtraction of new processes G4SteppingManager also aggregates e the pointers to G4Navigator from the geometry category to the current G4Track and the list of secondaries from the current track through a G4TrackVector toG4UserSteppingAction and to G4VSteppingVerbose It also has a use relation to G4ProcessManager and G4ParticleChange in the physics processes class category G4Track the class G4Track represents a particle which is pushed by G4SteppingManager It holds information required for stepping a particle for example the current position the time since the start of stepping the identification of the geometrical volume which contains the particle etc Dynamic information such as Design and Function of Geant4 Categories particle momentum and energy is held in the class through a pointer to the G4DynamicParticle class Static information such as the particle mass and charge is stored in the G4DynamicParticle class through the pointer to the G4ParticleDefinition class Here the aggregation hierarchical design is extensively employed to maintain high tracking performance e G4TrajectoryPoint and G4Trajectory the class G4TrajectoryPoint holds the state of the particle after propagating one step Among other things it includes information on space time energy momentum and geometrical volumes G4Trajectory aggregates all G4TrajectoryPoint objects which belong t
85. gt GetColour and there is a utility function G4VSceneHandler GetTextColour const G4Colour amp colour GetTextColour text 2 12 6 1 3 Solids For specific solids the G4PhysicalVolumeModel that provides the solids also provides via PreAddSolid a pointer to its vis attributes If the vis attribites pointer in the logical volume is zero it provides a pointer to the default vis attributes in the model which in turn is currently provided by the viewer s vis attributes see G4VSceneHandler CreateModelingParameters So the vis attributes pointer is guaranteed to be pertinent If the concrete driver does not implement AddSolid for any particular solid the base class converts it to primitives usually a G4Polyhedron and again the vis attributes pointer is guaranteed 2 12 6 1 4 Drawing style The drawing style is normally determined by the view parameters but for individual drawable objects it may be overridden by the forced drawing style flags in the vis attributes A utility function G4ViewParameters DrawingStyle G4VSceneHandler GetDrawingStyle is provided G4ViewParameters DrawingStyle drawing style GetDrawingStyle pVisAtts 2 12 6 1 5 Auxiliary edges Similarly the visibility of auxiliary soft edges is normally determined by the view parameters but may be overridden by the forced auxiliary edge visible flag in the vis attributes Again a utility function G4VSceneHandler GetAuxEdgeVisible is provided 29 Desig
86. hange e The secondaries from ParticleChange are stored to SecondaryL ist Then for each secondary t is checked if its kinetic energy is smaller than the energy threshold for the material In this case the particle is assigned a 0 kinetic energy and its energy is added as deposited energy of the parent track This check is only done if the flag ApplyCutFlag is set for the particle by default it is set to false for all particles user may change it in its GA VUserPhysicsList If the track has the flag IsGoodForTracking true this check will have no effect used mainly to track particles below threshold The parentID and the process pointer which created this track are set The secondary track is added to the list of secondaries If it has O kinetic energy it is only added if it it invokes a rest process at the beginning of the tracking The track is updated and its status is set according to what the process defined 2 4 5 Ordering of Methods of Physics Processes The ProcessManager of a particle is responsible for providing the correct ordering of process invocations G4SteppingManager invokes the processes at each phase just following the order given by the ProcessManager of the corresponding particle For some processes the order is important Geant4 provides by default the right ordering It is always possible for the user to choose the order of process invocations at the initial set up phase of Geant4 This default ordering is
87. he next level of abstraction only processes that occur for particles in flight are considered For these it is easily observed that the sources of cross sections and final state production are rarely the same Also different sources will come with different restrictions The principal use cases of the framework are addressing these commonalities A user might want to combine different cross sections and final state or isotope production models as provided by Geant4 and a physicist might want to implement his own model for particular situation and add cross section data sets that are relevant for his particular analysis to the system in a seamless manner Requirements 1 Flexible choice of inclusive scattering cross sections 2 Ability to use different data sets for different parts of the simulation depending on the conditions at the point of interaction 55 Extending Toolkit Functionality PN 9 Ability to add user defined data sets in a seamless manner Flexible unconstrained choice of final state production models Ability to use different final state production codes for different parts of the simulation depending on the conditions at the point of interaction Ability to add user defined final state production models in a seamless manner Flexible choice of isotope production models to run in parasitic mode to any kind of transport models Ability to use different isotope production codes for different parts of
88. hods and their specifications Note that the implementation details for some methods are not a trivial matter these methods must provide the functionality of finding whether a point is inside a solid finding the intersection of a line with it and finding the distance to the solid along any direction However once the solid class has been created with all its specifications fulfilled it can be used like any Geant4 solid as it implements the abstract interface of G4VSolid Other additions can also potentially be achieved For example an advanced user could add a new way of creating physical volumes However because each type of volume has a corresponding navigator helper this would require to create a new Navigator as well To do this the user would have to inherit from G4Navigator and modify the new Navigator to handle this type of volumes This can certainly be done but will probably be made easier to achieve in the future versions of the Geant4 toolkit 3 1 2 Adding a new type of Solid We list below the required methods for integrating a new type of solid in Geant4 Note that Geant4 s specifications for a solid pay significant attention to what happens at points that are within a small distance tolerance kCarTolerance in the code of the surface So special care must be taken to handle these cases in considering all different possible scenarios in order to respect the specifications and allow the solid to be used correctly by the other compo
89. hreadLocal in a POSIX system this is a typedef to __thread Unfortunately there are several constraints on what can be specified as TLS In particular the data member has to be declared static or be a global variable tinclude tls hh class G4Class private static G4ThreadLocal G4double fValue public G4Class b vb void SetMyData G4double aValue fValue aValue G4double GetMyData const return fValue y G4ThreadLocal G4double G4Class fValue 1 The problem occurs if we need more than one instance of type G4Class with an instance local different value of fValue How can this behavior be obtained now that the we have declared the data member as static The method used to solve this problem is called the split class mechanism The idea is to collect all thread local data fields into a separate new class instances of which one per original instance of G4Class are organized in an array This array is accessed via an index representing a unique identifier of a given class instance We can modify the code as follows class G4ClassData pulsi G4double fValue void intialize fValue 1 i y typedef G4Splitter gt G4ClassData lt G4ClassManager typedef G4ClassManager G4ClassSubInstanceManager tdefine G4MT_fValue subInstanceManager offset gClassInstanceId fValue class G4Class private G4int gClassInstanceld static G4ClassSubInstanceManager subInstanceManager public 37 Design and Funct
90. hysics list and primary generator action classes to it G4RunManager or a derived class must be a singleton This class provides several virtual methods that can be used to define user specific behavior for a Geant4 application G4RunManagerKernel provides control of the Geant4 kernel This class is constructed by G4RunManager This class does not provide virtual methods and user should not sub class from it The applicaiton G4RunManager shold own an instance of a G4RunManagerKernel singleton G4 MT Worker RunManager Kernel specialized versions to provide a multi threading enabled application Refer to chapter Parallelism in Geant4 multi threading capabilities for additional information G4VUserDetectorConstruction pure virtual base class that represents the simulation setup G4VUserParallel World pure virtual base class of the user s parallel world G4VUserPhysicsList pure virtual base class for a physcis list G4VUserPrimaryGeneratorAction pure virtual class used by user to define the primary generation G4VModularPhysicsList Pure virtual class to construct a physics list from G4VPhysicsConstructor More modern and modular approach preferred in current versions of pre packaged physics lists G4UserRunAction user action class for run Instantiate user derived G4Run and provides user hooks for begin and end of run G4UserWorkerlnitialization and G4UserWorkerThreadInitialization define here the concrete behavior for threading model B
91. imize the tracking time performance G4NavigationHistory responsible for maintenance of the history of the path taken through the geometrical hierarchy It is principally a utility class for use by G4Navigator G4NormalNavigation a utility class for navigation in volumes containing only G4PVPlacement daughter volumes e G4ParameterisedNavigation a utility class for navigation in volumes containing a single GAPV Parameterised volume for which voxels for the replicated volumes have been constructed G4VoxelNavigation a utility class for navigation in volumes containing only G4PVPlacement daughter volumes for which voxels have been constructed Design and Function of Geant4 Categories G4ReplicaNavigation a utility class for navigation in volumes containing a single G4PVParameterised volume for which voxels for the replicated volumes have been constructed G4PhysicalVolumeStore a container for optionally storing created physical volumes It enables traversal of all physical volumes by the Ul user etc All solids should be registered with G4PhysicalVolumeStore and removed on their destruction It is intended principally for the UI browser G4V PhysicalVolume a volume positioned within and relative to a given mother volume and also represented by a given logical volume They are optionally entered into the G4PhysicalVolumeStore G4PV Placement a physical volume corresponding to a single touchable detector element positioned w
92. in the Create method Optionally a context object can also be created with its own associated messengers For example ModelAndMessengers G4TrajectoryDrawByParticlelDFactory Create const G4String amp placement const G4String amp name Create default context and model G4VisTrajContext context new G4VisTrajContext default G4TrajectoryDrawByParticleID model new G4TrajectoryDrawByParticleID name context Create messengers for default context configuration AddContextMsgrs context messengers placement name Create messengers for drawer messengers push_back new G4ModelCmdSetStringColour G4TrajectoryDrawByParticleID model placement messengers push back new G4ModelCmdSetDefaultColour G4TrajectoryDrawByParticleID model placement messengers push back new G4ModelCmdVerbose G4TrajectoryDrawByParticleID model placement return ModelAndMessengers model messengers The new factory must then be registered with the visualisation manager This should be done by overriding the G4VisManager RegisterModelFactory method in a subclass See for example the G4VisManager implementation G4VisExecutive RegisterModelFactories RegisterModelFactory new G4TrajectoryDrawByParticleIDFactory 3 7 3 Trajectory Filtering 3 7 3 1 Creating a new trajectory filter model New trajectory filters must inherit at least from G4VFilter The models supplied with the Geant4 distribution inh
93. ing Fragmentation The base class for parton string models G4VParton StringModel declares the Get St rings pure virtual method G4VSt ring Fragmentation the pure abstract base class for string fragmentation declares the interface for string fragmentation To fulfill the requirements on intra nuclear transport two abstract classes are provided G4V3DNucleus and G4VScatterer At this point in time the usage of these intra nuclear transport related classes by concrete codes 1s not enforced by designs as the details of the cascade loop are still model dependent and more experience has to be gathered to achieve standardisation It is within the responsibility of the implementers of concrete intra nuclear transport codes to use the abstract interfaces as defined in these classes The class diagram is shown in Figure 3 6 for the string parton model aspects and in Figure 3 7 for the intra nuclear transport Framework functionality Again variants of Strategy Bridge and Chain of Responsibility are used GaVParton StringModel implements the initialisation of a three dimensional model of a nucleus and the logic of scattering It delegates secondary production to string fragmentation through a G4VString Fragmentation pointer It provides a registering service for the concrete string fragmentation and delegates the string excitation to derived classes Selection of string excitation is through selection of derived class Selection of string fragment
94. ingleton pattern the simplest of which is class G4Singleton public G4Singleton GetInstance static G4Singleton anInstance 41 Design and Function of Geant4 Categories return amp anInstance y With multi threading many managers and singletons are thread local For this reason they have been transformed to class G4Singleton private static G4ThreadLocal instance publio G4Singleton GetInstance if instance instance new G4Singleton return instance y This causes a memory leak it is not possible to delete thread local instances of the singletons To solve this problem the class G4ThreadLocalSingleton has been added to the toolkit This template class has a single public method T G4ThreadLocalSingleton lt T gt Instance that returns a pointer to a thread local instance of T The thread local instances of T will be deleted as in the case of G4Cache at the end of the program The example code can be transformed to tinclude G4ThreadLocalSingleton hh class G4Singleton friend class G4ThreadLocalSingleton lt G4Singleton gt publics G4Singleton GetInstance static G4ThreadLocalSingleton lt G4Singleton gt theInstance dco esmiseam ect 2 14 4 Threading model utilities and functions Geant4 parallelism is based on POSIX standards and in particular on the pthreads library However all functionalities have been wrapped around Geant4 specific names This allows the inclusion of the
95. ion of Geant4 Categories G4Class gClassInstanceId subInstanceManager CreateSubInstance void SetMyData G4double aValue G4MT_fValue aValue G4double GetMyData const return G4MT_fValue 5 G4ClassSubInstanceManager G4Class subInstanceManager template gt class G4ClassData lt G4ThreadLocal G4int G4Splitter gt G4ClassData lt workertotalspace 0 template gt class G4ClassData G4ThreadLocal G4int G4Splitter gt G4ClassData lt offset 0 As one can see the use of the value of fValue variable is very similar to how we use it in the original sequential mode all the handling of the TES is done in the template class G4Splitter that can be implemented as template lt class T gt class G4Splitter private G4int totalobj PUBLICO static G4ThreadLocal G4int workertotalspace static G4ThreadLocal T offset publ lcs G4Splitter totalobj 0 G4int CreateSubInstance 1 eot ullo if totalobj gt workertotalspace NewSubInstances return totalobj 1 void NewSubInstances if workertotalspace gt totalobj return G4int originaltotalspace workertotalspace workertotalspace totalobj 512 offset T realloc offset workertotalspace sizeof T if offset 0 G4Excepetion G4Splitter NewSubInstances OutOfMemory FatalException Cannot malloc space D for G4int i originaltotalspace i amp lt workertotalspace 1 offset i intialize
96. is not electromagnetic another minor modification may be required The transportation currently chooses whether to propagate a particle in a field or rectilinearly based on whether the particle is charged or not If your field affects non charged particles you must inherit from the G4Transportation andre implement the part of GetAlongStepPhysicalInteractionLength that decides whether the particles is affected by your force 50 Extending Toolkit Functionality In particular the relevant section of code does the following Does the particle have an EM field force exerting upon it Uy if particleCharge 0 0 fieldExertsForce this DoesGlobalFieldExist Future will can also check whether current volume s field is Zero or set by the user in the logical volume to be zero and you want it to ask whether it feels your force If for the sake of an example you wanted to see the effects of gravity on a heavy hypothetical particle you could say Does the particle have my field s force exerted on it if particle gt GetName VeryHeavyWIMP fieldExertsForce this DoesGlobalFieldExist For gravity After doing all these steps you will be able to see the effects of your force on a particle s motion Status of this chapter 10 06 02 partially re written by D H Wright 14 11 02 spell check by P Arce 3 3 Particles 3 3 1 Properties of particles The G4ParticleDefinition class contains the p
97. ithin and relative to a mother volume G4PVReplica a physical volume representing many identically formed touchable detector elements differing only in their positioning The elements positions are determined by means of a simple formula and the elements completely fill the containing mother volume G4PVParameterised a physical volume representing many touchable detector elements differing in their positioning and dimensions Both are calculated by means of a G4VParameterisation object Each element s position is calculated as per G4PVReplica and each element s shape can be modified by means of a user supplied formula G4VPVParameterisation a parameterisation class able to compute the transformation and indirectly the dimensions of parameterised volumes given a replication number G4SmartVoxelProxy a class for proxying smart voxels The class represents either a header in turn refering to more VoxelProxies or a node If created as a node calls to GetHeader cause an exception and likewise GetNode when a header G4SmartVoxelHeader represents a single axis of virtual division Contains the individual divisions which are potentially further divided along different axes G4SmartVoxelNode a single virtual division containing the physical volumes inside its boundaries and those of its parents G4VoxelLimits represents limitation restrictions of space where restrictions are only made perpendicular to the cartesian axes G4Solid
98. its amp pVoxelLimit const G4AffineTransform amp pTransform G4double amp pMin G4double amp pMax const Calculate the minimum and maximum extent of the solid when under the specified transform and within the specified limits If the solid is not intersected by the region return false else return true G4GeometryType GetEntityType const Provide identification of the class of an object required for persistency and STEP interface std ostream StreamInfo std ostream amp os const Should dump the contents of the solid to an output stream The method 46 Extending Toolkit Functionality G4VSolid Clone const should be implemented for every solid to provide a way to clone themselves in a new object with same specifications The method G4ThreeVector GetPointOnSurface const returns a random point located on the surface of the solid Points returned should not necessarily be uniformly distributed The method G4double GetCubicVolume should be implemented for every solid in order to cache the computed value and therefore reuse it for future calls to the method and to eventually implement a precise computation of the solid s volume If the method will not be overloaded the default implementation from the base class will be used estimation through a Monte Carlo algorithm and the computed value will not be stored The method G4double GetSurfaceArea should be implemented for every solid in
99. l and has been measured to be about 1 In this section we will discuss the details of how we achieve thread safety for different use cases The information contained here is of particular relevance for toolkit developers that need to adapt code to multi threading to increase performances typically to reduce the memory footprint of an application sharing between threads memory consuming objects It is however of general interest to understand some of the more delicate aspects of multi threading 2 14 3 2 Thread safety and sharing of objects To better understand how memory is handled and what are the issues introduced by multi threading it is easier to proceed with a simplified example Let us consider the simplest possible class G4Class that consists of a single data member class G4Class 33 Design and Function of Geant4 Categories static G4double fValue static keyword is optional y Our goal is to transform the code of G4Class to make it thread safe A class or better a method of a class is thread safe if more than one thread can simultaneously operate on the class data member or its methods without interfering with each other in an unpredictable way For example if two threads concurrently write and read the value of the data field fValue and this data field 1s shared among threads the two threads can interfere with each other if no special code to synchronize the thread is added This condition is called data race and i
100. lumes and which may have other attributes It has access to other information which is independent of its phyisical location in the detector such as material and sensitive detector behavior A physical volume represents the spatial positioning or placement of the logical volume with respect to an enclosing mother logical volume Thus a hierarchical tree structure of volumes can be built with each volume containing smaller volumes which may not overlap Repetitive structures can be represented by specialized physical volumes such as replicas and parameterized placements sometimes resulting in a large savings in memory In Geant4 the logical volume has been refined by defining the shape as a separate entity called a solid Solids with simple shapes like rectilinear boxes trapezoids spherical or cylindrical sections or shells each have their properties coded separately in accord with the concept of Constructed Solid Geometry CSG More complex solids are defined for specific use or having their surfaces approximated by facets tessellated solids Another way to build solids is by Boolean combination union intersection and subtraction The elemental solids should be CSGs Although a detector is naturally and best described as by a hierarchy of volumes efficiency is not critically dependent on this An optimization technique called voxelization allows efficient navigation even in flat geometries typical of those produced by CAD system
101. mentation frameworks used in and provided by Geant4 for hadronic shower simulation as in the 1 1 release of the program The implementation frameworks follow the Russian dolls approach to implementation framework design A top level very abstracting implementation framework provides the basic interface to the other Geant4 categories and fulfils the most general use case for hadronic shower simulation It is refined for more specific use cases by implementing a hierarchy of implementation frameworks each level implementing the common logic of a particular use case package in a concrete implementation of the interface specification of one framework level above this way refining the granularity of abstraction and delegation This defines the Russian dolls architectural pattern Abstract classes are used as the delegation mechanism All framework functional requirements were obtained through use case analysis In the following we present for each framework level the compressed use cases requirements designs including the flexibility provided and illustrate the framework functionality with examples All design patterns cited are to be read as defined in Gammal1995 3 5 3 Level 1 Framework processes There are two principal use cases of the level 1 framework A user will want to choose the processes used for his particular simulation run and a physicist will want to write code for processes of his own and use these together with the rest of th
102. mplate class T class F gt G4double G4Integrator lt T F gt Legendre96 T typeT F f G4double a G4double b A Returns the integral of the function to be pointed by T f between a and b by 96 point Gauss Legendre integration the function is evaluated exactly ten Times at interior points in the range of integration Since the weights and abscissas are in this case symmetric around the midpoint of the range of integration there are actually only five distinct values of each Convenient for using with some class object typeT The method is very accurate and fast enough Roots and weights are from Abramowitz M Stegan I A 1964 Handbook of Math p 919 template class T class F gt G4double G4Integrator lt T F gt Chebyshev T typeT F f G4double a G4double b G4int nChebyshev Ui Integrates function pointed by T f from a to b by Gauss Chebyshev quadrature method Convenient for using with class object typeT template class T class F gt G4double G4Integrator lt T F gt Laguerre T amp typeT F f G4double alpha G4int nLaguerre Li L Integral from zero to infinity of sid spowts elona stds cep e F x The value of nLaguerre sets the accuracy The function creates arrays fAbscissa 0 nLaguerre 1 and fWeight 0 nLaguerre 1 Convenient for using with class object typeT and typeT f function HP ARES template lt class T class F gt G4double G4
103. n low background experiment 3 5 5 Level 3 Framework Theoretical Models lt lt Abstracto gt G4Hadronicinteraction lt lt Concrete gt gt lt lt Concrate gt gt G4TheoFSGenerator G4PartonTransportModel Paro YousoNo lt lt Purely Abstracts G4VPreCompoundModel Pr SApplyYouself SoeExcite SSetEx landier lt lt Concrete gt gt G4PythiaAhInterface gt G4VHighEnergyGenerator 1 o DR ae lt lt Abstract gt gt G4VintraNuclearTransportModel G4NhModel lt lt Abstract gt gt scatter S GetWoundedNucleus G4VPartonStringModel apply Yourself scatter SGetWoundedNucleus it Pcevituab gt GetStrings AcorrectHacronMomenta lt lt Concrates gt G4PythiaNhinterface PPSetThisPointer G4HadronKineticModel G4QMDModel G4HadronicCascade ji L lt lt Concrete gt gt lt lt Concrete gt gt lt lt Concrete gt gt Figure 3 5 Level 3 implementation framework of the hadronic category of Geant4 theoretical model aspect Geant4 provides at present one implementation framework for theory driven models The main use case is that of a user wishing to use theoretical models in general and to use various intra nuclear transport or pre compound models together with models simulating the initial interactions at very high energies Requirements 1 Allow to use or adapt any string parton or parton transport VNI 58 Extending Toolkit Functionality
104. n System altogether 2 12 3 The Geant4 Visualisation System The Geant4 Visualisation System consists of G4VisManager An implementation of the G4VVisManager interface It manages multiple graphics systems and defines three more concepts the scene G4Scene the scene handler base class G4VSceneHandler itself a sub class of G4VGraphicsScene and the viewer base class G4V Viewer see below G4VisManager is a singleton and an abstract class requiring the user to derive from it a concrete visualisation manager G4VisExecutive is provided see below Roles and structure of the visualisation manager are described in Chapter 8 of the User s Guide for Application Developers G4VisExecutive A concrete visualisation manager that implements the virtual functions RegisterGraphicsSystems and RegisterModelFactories These functions must be in the users domain since the graphics systems and models that are instantiated by them are in many cases provided by the user graphics libraries etc It is therefore implemented as a hh icc combination that is designed to be included in the users code Of course the user may write his or her own e G4Scene The scene is a list if models for physical volumes axes hits trajectories etc see Section Section 2 12 4 They are distinguished according to their lifetime run duration for physical volumes etc end of event for hits and trajectories etc The end of event models are only to be us
105. n and Function of Geant4 Categories G4bool isAuxEdgeVisible GetAuxEdgeVisible pVisAtts 2 12 6 1 6 LineSegmentsPerCircle Also the precision of rendering curved edges in the polyhedral representation of volumes is normally determined by the view parameters but may be overridden by a forced attribute A utility function that respects this G4VSceneHandler GetNoOfSides is provided For example G4Polyhedron SetNumberOfRotationSteps GetNoOfSides pVisAttribs 2 12 6 1 7 Marker size These have nothing to do with vis attributes they are an extra property of markers i e objects that inherit G4V Marker circles squares text etc However the algorithm for the actual size is quite complicated and a utility function G4VSceneHandler GetMarkerSize is provided MarkerSizeType sizeType G4double size GetMarkerSize text sizeType sizeType is world or screen signifying that the size is in world coordinates or screen coordinates respectively Status of this chapter 27 06 05 partially re organized and section on design philosophy added from Geant4 general paper by D H Wright 13 10 05 Section on vis attributes added by John Allison 06 01 06 Re write of Design Philosphy and introduction of The Graphics Interfaces and The Geant4 Visualisation System by John Allison Dec 2006 Conversion from latex to Docbook verson by K Amako 2 13 Intercoms 2 13 1 Design Philosophy The intercoms category implements an ex
106. n the viewing window This is then the standard view and any further operations requested by the user zoom pan etc are relative to this standard view The class G4ViewParameters has utility routines to assist this procedure it is strongly advised that toolkit developers writing a viewer should study the G4ViewParameters class whose header file contains much useful information also preserved in the Software Reference Manual The viewer is messaged by the vis manager when the user issues commands such as vis viewer refresh This invokes methods such as SetView ClearView and DrawView A detailed description of the call sequences is given in Section 3 7 1 2 Section 3 7 1 5 Note there is no restriction on the number or type of scene handlers or viewers There may be several scene handlers processing the same or different scenes each with several viewers for example the same scene from differing viewpoints 26 Design and Function of Geant4 Categories By defining a set of three C classes inheriting from the virtual base classes G4VGraphicsSystem G4VSceneHandler and G4VViewer an arbitrary graphics system can easily be plugged in to Geant4 The plugged in graphics system is then available for visualising detector simulations Together this set of three concrete classes is called a visualisation driver The DAWN File driver for example is the interface to the Fukui Renderer DAWN and is implemented by the following set
107. nctions virtual void Draw const G4VTrajectory amp G4int i_mode 0 const G4bool amp visible true const 0 virtual void Print std ostream ostr const 0 To use the new model directly in compiled code simply register it with the G4VisManager eg G4VisManager visManager new G4VisExecutive visManager gt Initialise Create custom model MyCustomTrajectoryModel myModel new MyCustomTrajectoryModel custom Configure it if necessary then register with G4VisManager Sieve Tag ee Shay Laue midds Dase 3 7 2 2 Adding interactive functionality Additional classes need to be written if the new model is to be created and configured interactively Messenger classes Messengers to configure the model should inherit from G4VModelCommand The concrete trajectory model type should be used for the template parameter eg class G4MyCustomModelCommand public G4VModelCommand G4TrajectoryDrawByParticleID A number of general use templated commands are available in G4ModelCommandsT hh Factory class 74 Extending Toolkit Functionality A factory class responsible for the model and associated messenger creation must also be written The factory should inherit from G4V ModelFactory The abstract model type should be used for the template parameter eg class G4TrajectoryDrawByChargeFactory public G4VModelFactory lt G4VTrajectoryModel gt y The model and associated messengers should be constructed
108. nd Model and provides concrete intra nuclear transports with the possibility of delegating pre compound decay to these models G4VPreCompoundModel provides a registering mechanism for compound decay through the GAVExcitation Handler interface and provides concrete implementations with the possibility of delegating the decay of a compound nucleus The concrete scenario of GAaTheoFS Generator using a dual parton model and a classical cascade which in turn uses an exciton pre compound model that delegates to an evaporation phase would be the following GA4TheoFS Generator receives the conditions of the interaction a primary particle and a nucleus It asks the 59 Extending Toolkit Functionality dual parton model to perform the initial scatterings and return the final state along with the by then damaged nucleus The nucleus records all information on the damage sustained GATheoFS Generator forwards all information to the classical cascade that propagates the particles in the already damaged nucleus keeping track of interactions further damage to the nucleus etc Once the cascade assumptions break down the cascade will collect the information of the current state of the hadronic system like excitation energy and number of excited particles and interpret it as a pre compound system It delegates the decay of this to the exciton model The exciton model will take the information provided and calculate transitions and emissions until
109. nd include G4Allocator 20 Design and Function of Geant4 Categories G4FastVector G4ReferenceCountedHandle e G4PhysicsVector G4LPhysicsFreeVector G4PhysicsOrderedFreeVector G4Timer G4UserLimits G4UnitsTable A general description of these classes is given in section 3 2 of the Geant4 User s Guide for Application Developers The module includes wrappers to most CLHEP classes used in Geant4 and tools for memory management G4Cache G4AutoDelete and for threading G4AutoLock G4Threading G4ThreadLocalSingleton G4TWorkspacePoo1 It also provides specialised fast implementations for some heavily used mathematical functions like G4Exp G4Log G4Pow In applications where it is necessary to generate random numbers normally from the same engine in many different methods and parts of the program it is highly desirable not to rely on or require knowledge of the global objects instantiated By using static methods via a unique generator the randomness of a sequence of numbers is best assured Hence the use of a static generator has been introduced in the original design of HEPRandom as a project requirement in Geant4 2 11 2 Class Design Analysis and design of the HEPRandom module have been achieved following the Booch Object Oriented methodology Some of the original design diagrams in Booch notation are reported below Figure 2 21 is a general picture of the static class diagram HepRandomEngine abstract
110. nents of the geometry module Creating a derived class of G4VSolid The solid must inherit from G4VSolid or one of its derived classes and implement its virtual functions Mandatory member functions you must define are the following pure virtual of G4VSolid EInside Inside const G4ThreeVector amp p G4double DistanceToIn const G4ThreeVector amp p G4double DistanceToIn const G4ThreeVector amp p const G4ThreeVector amp v G4ThreeVector SurfaceNormal const G4ThreeVector amp p G4double DistanceToOut const G4ThreeVector amp p G4double DistanceToOut const G4ThreeVector amp p const G4ThreeVector v const G4bool calcNorm false G4bool validNorm 0 G4ThreeVector n G4bool CalculateExtent const EAxis pAxis const G4VoxelLimits amp pVoxelLimit const G4AffineTransform amp pTransform G4double amp pMin G4double amp pMax const G4GeometryType GetEntityType const std ostream StreamInfo std ostream amp os const They must perform the following functions EInside Inside const G4ThreeVector amp p This method must return 45 Extending Toolkit Functionality kOutside if the point at offset p is outside the shape boundaries plus Tolerance 2 kSurface if the point is lt Tolerance 2 from a surface or kInside otherwise G4ThreeVector SurfaceNormal const G4ThreeVector amp p Return the outwards pointing unit normal of the shape for the surface closest to the point at offset p G4double DistanceToIn
111. ng thrown by explicitly specifying an engine which can be shared by many distribution objects The static interface is skipped here 22 Design and Function of Geant4 Categories localEngine 1 flat e 0 9 flat 4 A M 7 flat 10 fire 5 flat PoissonDi 3 flat 0 T stribution 2 fire y fire fi fi Flatbisti y 4 fire ye fire BWDistribu ution ue fon ExpDistrib GaussDist ution ribution Figure 2 23 Shooting via distribution objects Figure 2 24 illustrates the situation when many generators are defined each by a distribution and an engine The static interface is skipped here Engines tiflat Cw 9 flat 4 N 7 flat 10 shoot 3 flat 5 fiat gt PoissonDi 8 shoot stribution 2 shoot 4 i FlatDistrib y 4 shoot 6 shoot BWDistrib ution N ution ExpDistrib GaussDist ution ribution Figure 2 24 Shooting with arbitrary engines For detailed documentation about the HEPRandom classes see the CLHEP Reference Guide http cern ch clhep manual RefGuide or the CLHEP User Manua http cern ch clhep manual UserGuide Informations written in this manual are extracted from the original manifesto distributed with the HEPRandom package http cern ch clhep manual UserGuide Random Random html HEPNumerics The HEPNumerics module includes a set of classes which implement numerical algorithms for general use in Geant4 The User s Guide for Application Developers contai
112. nging particle properties Only in the PreInit phase can properties be modified with the help of the G4ParticlePropertyTable class Particle properties can be overridden with the method G4bool SetParticleProperty const G4ParticlePropertyData amp newProperty 51 Extending Toolkit Functionality by setting new values in G4ParticlePropertyData In addition the current particle property values can be extracted to text files by using G4TextPPReporter On the other hand G4TextPPRetriever can change particle properties according to text files 3 3 2 Adding New Particles A new particle can be added by creating a new class for it The new class should be derived from G4ParticleDefinition You can find an example under examples extended exoticphysics monopole There the new class for the monopole is defined as follows class G4Monopole public G4ParticleDefinition private static G4Monopole theMonopole G4Monopole const G4String amp aName G4double mass G4double width G4double charge G4int menm G4int iParity G4int iConjugation G4int ilsospin G4int ilsospin3 G4int gParity const G4String amp pType G4int lepton G4int baryon G4int encoding G4bool stable G4double lifetime G4DecayTable decaytable public virtual G4Monopole static G4Monopole MonopoleDefinition static G4Monopole Monopole The static methods above must be defined and implemented so that the new particle instance will be
113. ngs 1 e4Particeciangerort oss lo G4PIocessAtirbuie GaProcTDEemem e 3 feGreatorProceds ble 3 ILengihLef EnTra po Il fpPravessDafinadStep GiWroppetProcess GiStepPoint GivResrconinuouspiscreteProcess cavresiprocess GavcommuousProcess Gavorscreteprocess GavcommuouspiscreteProcess GsvkestcommuousProcess cavrestoiscreteprocess Figure 2 7 Management of Physics Processes Status of this chapter 27 06 05 section on design philosophy added by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 6 Hits and Digitization 2 6 1 Design Philosophy In Geant4 a hit is a snapshot of a physical interaction or an accumulation of interactions of a track or tracks in a sensitive detector component A digitization or digit represents a detector output such as an ADC TDC count or a trigger signal A digit is created from one or more hits and or other digits Given the wide variety of Geant4 applications ways of describing detector sensitivity and the quantities to be stored in the hits and digits vary greatly This category therefore provides only abstract classes for both detector sensitivity and hits digits It also provides tools for organizing the hits digits into collections 2 6 2 Class Design G4SensitiveDete
114. ns a description of each class Most of the algorithms were implemented using methods from the following books B H Flowers An introduction to Numerical Methods In C Claredon Press Oxford 1995 M Abramowitz I Stegun Handbook of mathematical functions DOVER Publications INC New York 1965 chapters 9 10 and 22 The HEPNUmerics module provides general mathematical methods supporting Geant4 Monte Carlo simulation processes Among these there are methods for function and array interpolations using known special functions class method integration solving polynomial equation up to 4th order and some others Of particular interest is the templated class G4Integrator which consists of methods allowing to integrate class methods Since the type whose method should be integrated is not known in advance G4Integrator uses templated signatures and pointers to functions in its API It provides both usual numerical methods like adaptive Gauss or Simpson integration and more sofisticated faster and at the same accurate methods based on the orthogonal polynomials 23 Design and Function of Geant4 Categories Among the different integration methods involving orthogonal polynomials there are Gauss Legendre Gauss Chebyshev Gauss Hermite and Gauss Jacobi methods template class T class F G4double G4Integrator lt T F gt Legendre T amp typeT F f G4double a G4double b G4int nLegendre The value nLegendre set
115. nteractions All particles are based on the G4ParticleDefinition class which describes basic properties such as mass charge etc and also allows the particle to carry a list of processes to which it is sensitive A first level extension of this class defines the interface for particles that carry cuts information for example range cut versus energy cut equivalence A set of virtual intermediate classes for leptons bosons mesons baryons etc allows the implementation of concrete particle classes which define the actual particle properties and in particular implement the actual range versus energy cuts equivalence All concrete particle classes are instantiated as singletons to ensure that all physics processes refer to the same particle properties 2 9 2 Class Design The object oriented design of the particles related classes is shown in the following class diagrams The diagrams are described in the Booch notation Figure 2 15 shows a general overview of the particle classes Figure 2 17 shows classes related to the particle table and Figure 2 16 shows the classes related to the ion table in the particle table Figure 2 18 shows the classes related to the particle decay table in the G4ParticleDefinition This decay tabele is used by decay process and Figure 2 19 shows the classes related to the decay process and decay channels 17 Design and Function of Geant4 Categories G4PDefManager subinstanceManager G4ParticleTable
116. o rE E E I He mee a EE 68 3 7 2 Enhanced Trajectory Drawing cuicos distro sea beendet te ceteet yeh ates Dee ASH o tore tones 74 373s Trajectory AA eer eee eti e oT ee een 75 3 74 Other Resources aote ceret te eh eese E eto tos p eer swede cul sates Codex ee beet 76 Ioljijuria E EE TI Chapter 1 Introduction 1 1 Scope of this manual The User s Guide for Toolkit Developers provides detailed information about the design of Geant4 classes as well as the information required to extend the current functionality of the Geant4 toolkit This manual is designed to provide a repository of information for those who want to understand or refer to the detailed design of the toolkit and provide details and procedures for extending the functionality of the toolkit so that experienced users may contribute code which is consistent with the overall design of Geant4 This manual is intended for developers and experienced users of Geant4 It is assumed that the reader is already familiar with functionality of the Geant4 toolkit as explained in the User s Guide For Application Developers and also has a working knowledge of programming using C A knowledge of object oriented analysis and design will also be useful in understanding this manual It is also useful to consult the Software Reference Manual which provides a list of Geant4 classes and their major methods Detailed discussions of the physics included in Geant4 are provided in the
117. o the particle being propagated G4TrackingManager takes care of adding the G4TrajectoryPoint toaG4Trajectory object if the user requested it see Geant4 User s Guide For Application Developers The life of a G4Trajectory object spans an event contrary to G4Track objects which are deleted from memory after being processed G4UserTrackingAction and G4UserSteppingAction G4UserTrackingAction is a base class from which user actions at the beginning or end of tracking may be derived Similarly GAUserSteppingAction 1s a base class from which user actions at the beginning or end of each step may be derived 2 4 3 Tracking Algorithm The key classes for tracking in Geant4 are G4TrackingManager and G4SteppingManager The singleton object TrackingManager from G4TrackingManager keeps all information related to a particular track and it also manages all actions necessary to complete the tracking The tracking proceeds by pushing a particle by a step the length of which is defined by one of the active processes The TrackingManager object delegates management of each of the steps to the SteppingManager object This object keeps all information related to a particular step The public method ProcessOneTrack in G4TrackingManager is the key to managing the tracking while the public method Stepping is the key to managing one step The algorithms used in these methods are explained below ProcessOneTrack in G4TrackingManager Actions
118. of classes 1 GAaDAWNFILE public G4VGraphicsSystem for creation of the scene handlers and viewers 2 GADAWNFILESceneHandler public G4VSceneHandler for modeling 3D scenes 3 GADAWNFILEView public GAV View for rendering 3D scenes Several visualisation drivers are distributed with Geant4 They are complementary to each other in many aspects For details see Chapter 8 of the User s Guide for Application Developers 2 12 4 Modeling sub category G4VModel a base class for visualisation models A model is a graphics system independent description of a Geant4 component The sub category visualisation modeling defines how to model a 3D scene for visualisation The term 3D scene indicates a set of visualisable component objects put in a 3D world A concrete class inheriting from the abstract base class GAVModel defines a model which describes how to visualise the corresponding component object belonging to a 3D scene G4ModelingParameters defines various associated parameters For example G4PhysicalVolumeModel knows how to visualise a physical volume It describes a physical volume and its daughters to any desired depth G4HitsModel knows how to visualise hits G4TrajectoriesModel knows how to visualise trajectories The main task of a model is to describe itself to a 3D scene by giving a concrete implementation of the following virtual method of G4VModel virtual void DescribeYourselfTo G4VGraphicsScene amp 0 The argument cl
119. on point for threads to be implemented A detailed example on the use of conditions and how to implement correctly a barrier is discussed in G4MTRunManager code at the end of file source run src G4MTRunManager cc In general there should be no need for kernel classes with the exception of run category to use conditions since threads are considered independent and do not need to communicate between them 2 14 5 Additional material In this chapter we discussed in detail what are probably the most critical aspects of multi threading capabilities in Geant4 Additional material can be found in online resources The main entry point is the Geant4 multi threading 43 Design and Function of Geant4 Categories task force twiki page The Application Developers Guide contains general information regarding multi threading that is also relevant for Toolkit Developers A beginners guide to multi threading targeted to Geant4 developers has been presented during the 18th Collaboration Meeting agenda For additional information consult this page and this page Several contributions at the 18th Collaboration Meeting discuss multi threading Plenary Session 3 Geant4 version 10 part 1 agenda Hadronics issues related to MT agenda Developments for multi threading work spaces contribution Status of the planned developments coding guidelines MT migration g4tools migration code review contribution e G4MT CP on MIC Architecture cont
120. onAt G4double length const 0 that are used in these weights calculations It defines also the pure virtual method e virtual G4double SampleInteractionLength 0 In the case of the occurence biasing the dedicated virtual const G4VBiasingOperation ProvideOccurenceBiasingInteractionLaw const G4BiasingProcessInterface callingProcess G4ForceCondition amp proposeForceCondition 0 is meant to return the biased law The G4BiasingProcessInterface will not change the state of the law It will collect the sampled interaction length that the biasing operation must have asked to law to sample and will used the non interaction probability method in its AlongStepDolIt to compute the weight for non interaction these weight being multiplied among biased processes and it will use the effective cross section of process i if process i wins the interaction length race in its PostStepDoIt to compute the weight for interaction nin 1 To compute these weights the G4BiasingProcessInterface holds a private interaction law to which it sets the analog process cross section that it collects at the beginning of the step As occurence biasing and final state biasing are independent operations the weight correction for interaction due to the occurence biasing is applied on top of the final state generated by the process this final state being biased or not 3 7 Visualisation This Chapter is intended to be read aft
121. onsidered as the main and higher level application programming interface APT used in a Geant4 application A simple applicaiton will use concrete classes provided with the toolkit the developer will provide the detector description a primary genertor possibly using one of the general purpose ones provided with the toolkit define the physics for the application the physics list possibly one of the few provided with the toolkit and optional user actions to interact with the simulation itself In few cases it is however necessary to modify the default behavior of one or more classes in this category to allow for a user customization As an example the class GIMTRunManager extends the basic run manager class to take into account event level parallelism via multi threading During a run some states of the application are invariant and cannot be modified the physics list i e the list of processes attached to each particle and the detector layout not that some geometry primitives allow for changing parameters during the event run parametrizations However technically the class instances representing the detector layout do not change during a run 2 2 2 Class Design The relevant classes for the run category are shown here This show in particular the relation between classes for the case of a multi threaded application For a sequential applicaiton the diagram is simplified since no G4WorkerRunManager class exist and GAMTRunManager is replace
122. onstraints of the toolkit It also defines three types of users characterized by their level of interaction with the system Specific requirements are also listed and classified Status of this chapter 24 06 05 re organized and re written by D H Wright Chapter 2 Design and Function of Geant4 Categories 2 1 Introduction Geant4 exploits advanced software engineering techniques based on the Booch UML Object Oriented Methodology and follows the evolution of the ESA Software Engineering Standards for the development process The spiral or iterative approach has been adopted User requirements were collected in the initial phase and problem domain decomposition object oriented methods and CASE tools were used for analysis and design This produced a clear hierarchical structure of sub domains linked by a uni directional flow of dependencies This led to a software product which is modular and flexible a toolkit and in which the physics implementation is transparent and open to user validation of physics predictions It allows the user to understand customize and extend the toolkit in all domains At the same time the modular architecture allows the user to load only needed components 2 2 Run 2 2 1 Design Philosophy The run category manages collections of events runs In a single run the events share the detector implementation physics conditions and primary generation The classes associated with the run category can be c
123. oth classes provide several virtual methods that can be modified in derived classes G4VUserActionInitialization pure virtual class used by user to instantiate concrete instances of the user actions G4Worker Thread this class encapsulates thread specific data G4RNGHelper helper class to register and use RNG seeds Used by MT applicaitons to guarantee reproducibility Design and Function of Geant4 Categories Status of this chapter 28 06 05 under construction December 2006 Converted from latex to Docbook by K Amako July 2014 Review and new documnetation for MT by A Dotti 2 3 Event 2 3 1 Design Philosophy In high energy physics the primary unit of an experimental run is an event An event consists of a set of primary particles produced in an interaction and a set of detector responses to these particles In Geant4 objects of the G4Event class are the primary units of a simulation run Before the event is processed it contains primary vertices and primary particles produced by an external physics generator After the event is processed it may also contain hits digitizations and optionally trajectories generated by the simulation The event category manages events and provides an abstract interface to external physics generators G4Event and its content vertices and particles are independent of other classes This isolation allows Geant4 based simulation programs to be independent of specific choices for physics g
124. pandable command interpreter which is the key mechanism in Geant4 for realizing customizable and state dependent user interactions with all categories without being perturbed by the dependencies among classes The capturing of commands is handled by a C abstract class G4Ulsession Various concrete implementations of the command capturer are contained in the user interfaces category Taking into account the rapid evolution of graphical user interface GUI technology and consequent dependence on external facilities plural and extensible GUIs are offered Programmers need only know how to register the commands and parameters appropriate to their problem domain no knowledge of GUI programming is required to allow an application to use them through one of the available GUIs The intercoms category also provides the virtual base classes G4VVisManager G4VGraphicsScene and G4VGlobalFastSimulationManager 2 13 2 Class Design e G4UISession 30 Design and Function of Geant4 Categories e G4UlBatch G4UICommand G4Ulparameter G4Ulmessenger G4UIExecutive A concrete interface manager It will register the UI selected by the environment variable set It will take first by defaul the following order GAUI USE QT G4UI USE XM GAUI USE WIN32 GAUI USE TCSH Terminal The object oriented design of the user interface related classes is shown in the class diagram Figure 2 25 The diagram is described in the Booch
125. r GetConcreteInstance if pVVisManager pVVisManager gt Draw G4Circle Note that this allows the building an application without a concrete implementation for example for a batch job even if some code like the above is still included Most of the novice examples can be built this way if G4VIS_NONE is specified The concrete implementation of this interface is hereafter referred to as the visualisation manager 25 Design and Function of Geant4 Categories G4VGraphicsScene The visualisation manager must also provide a concrete implementation of the subsidiary interface G4VGraphicsScene It is only for use by the kernel and the modeling category It offers direct access to a scene handler through a reference provided by the visualisation manager It is described in more detail in the section on extending the toolkit functionality The Geant4 distribution includes implementations of the above interfaces namely G4VisManager and G4VSceneHandler respectively and their associated classes These define further abstract base classes for visualisation drivers Together they form the Geant4 Visualisation System A variety of concrete visualisation drivers are also included in the distribution Details of how to implement a visualisation driver are given in Section 3 7 Of course it is always possible for a user to implement his or her own concrete implementations of G4V VisManager and G4VGraphicsScene replacing the Geant4 Visualisatio
126. rack G4Nucleus amp G4HadronicProcess provides a registry for final state production models inheriting from G4Hadronic Interaction Again final state production model is meant in very general terms This can be an implementation of a quark gluon string model QGSM a sampling code for ENDF B data formats ENDFForm or a parametrisation describing only neutron elastic scattering off Silicon up to 300 MeV Isotope production For isotope production a base class G4VIsotope Production is provided It declares a method G4IsoResult GetIsotope const G4Track const G4Nucleus amp that calculates and returns the isotope production information Any concrete isotope production model will inherit from this class and implement the method Again the modeling possibilities are not limited and the implementation of concrete production models is not restricted in any way By convention the Get Isotope method returns NULL if the model is not applicable for the current projectile target combination Framework functionality Cross Sections G4HadronicProcess provides registering possibilities for data sets A default is provided covering all possible conditions to some approximation The process stores and retrieves the data sets through a data store that acts like a FILO stack a Chain of Responsibility with a First In Last Out decision strategy This allows the user to map out 57 Extending Toolkit Functionality the entire parame
127. reated from this The G4VisExtent must presumably be given the minus x plus x minus y plus y minus z and plus z extents of this box For example a cylinder can say G4VisExtent G4Tubs GetExtent const Define the sides of the box into which the G4Tubs instance would fit return G4VisExtent fRMax fRMax fRMax fRMax fDz fDz The method G4Polyhedron CreatePolyhedron const is required by the visualisation system in order to create a realistic rendering of your solid To create a G4Polyhedron for your solid consult G4Polyhedron While the method G4Polyhedron GetPolyhedron const is a smart access function that creates on requests a polyhedron and stores it for future access and should be customised for every solid 3 1 3 Modifying the Navigator For the vast majority of use cases it is not indeed necessary and definitely not advised to extend or modify the existing classes for navigation in the geometry A possible use case for which this may apply is for the description of a new kind of physical volume to be integrated We believe that our set of choices for creating physical volumes is varied enough for nearly all needs Future extensions of the Geant4 toolkit will probably make easier exchanging or extending the G4Navigator by introducing an abstraction level simplifying the customisation At this time a simple abstraction level of the navigator is provided by allowing overloading of the relevant f
128. ribution Finally a few articles and proceedings have been prepared X Dong et al Creating and Improving Multi Threaded Geant4 Journal of Physics Conference Series 396 no 5 p 052029 X Dong et al Multithreaded Geant4 Semi automatic Transformation into Scalable Thread Parallel Software Euro Par 2010 Parallel Pro cessing 2010 vol 6272 pp 287 303 S Ahn et al Geant4 MT bringing multi threaded Geant4 into production to be published in SNA amp MC2013 proceeding Status of this chapter January 2014 revised for spelling and grammar December 2013 First version Adapted from Multi threading task force twiki web pages 44 Chapter 3 Extending Toolkit Functionality 3 1 Geometry 3 1 1 What can be extended Geant4 already allows a user to describe any desired solid and to use it in a detector description in some cases however the user may want or need to extend Geant4 s geometry One reason can be that some methods and types in the geometry are general and the user can utilise specialised knowledge about his or her geometry to gain a speedup The most evident case where this can happen is when a particular type of solid is a key element for a specific detector geometry and an investment in improving its runtime performance may be worthwhile To extend the functionality of the Geometry in this way a toolkit developer must write a small number of methods for the new solid We will document below these met
129. roperties which characterize individual particles such as name mass charge spin and so on Properties of particles are set during the initialization of each particle type The default values of these properties are described in each particle class In the case of heavy nuclei properties may be given by external files Once initialized particle properties cannot be changed except for those related to its decay these are life time branching ratio of each decay mode and the stable flag Geant4 proivides a method to override these properties by using external files Properties of nuclei Individual classes are provided for light nuclei i e deuteron triton He3 and He4 with default values of their properties Other nuclei are dynamically created by requests from processes and users G4IonTable class handles the creation of such ions Default properties of nuclei are determined with help of G4NuclearProperties Users can register a G4IsotopeTable to the G4IonTable G4IsotopeTable which describes the properties used to create ions Excitation energy decay modes and life times for relatively long lived nuclei can be obtained by using G4RIsotopeTable and data files such as those pointed to by the GERADIOACTIVEDATA environment variable G4IsotopeMagneticMomentTable provides a table of nuclear magnetic moments using the data file G4IsotopeMagneticMoment table The environment variable GEFIONMAGNETICMOMENT should be set to point to this file Cha
130. s 2 7 2 Class Design G4GeometryManager responsible for managing high level objects in the geometry subdomain notably including opening and closing locking the geometry and creating deleting optimization information for G4Navigator The class is a singleton G4LogicalVolumeStore a container for optionally storing created logical volumes It enables traversal of all logical volumes by the Ul user etc G4LogicalVolume represents a leaf node or unpositioned subtree in the geometry hierarchy It may have daughters ascribed to it and is also responsible for retrieval of the physical and tracking attributes of the physical volume that it represents These attributes include solid material magnetic field and optionally user limits sensitive detectors etc Logical volumes are optionally entered into the G4LogicalVolumeStore G4MagneticField a class responsible for the magnetic field in each volume including the calculation of particle trajectories along curved paths In cases where the geometry step limits the particle s step the distance calculated is guaranteed to be the distance to a volume boundary G4Navigator a class used by the tracking management able to obtain calculate tracking time geometrical information such as distance to the next volume or to find the physical volume containing a given point in the world reference system The navigator maintains a transformation history and other information used to opt
131. s and positions The base class for pre equilibrium decay models GAVPre CompoundModel inherits from G4Hadronic Interaction again making any concrete implementation usable as stand alone model It adds a pure virtual DeExcite method for further evolution of the system when intra nuclear transport assumptions break down DeExcite takes a G4Fragment the Geant4 representation of an excited nucleus as argument The base class for evaporation phases G4VExcitation Handler declares an abstract method BreakItUP for compound decay Framework functionality The G4TheoFSGenerator class inherits from G4Hadronic Interaction and hence can be registered as a model for final state production with a hadronic process It allows a concrete implementation of G4VIntranuclear TransportModel and G4VHighEnergy Generator to be registered and delegates initial interactions and intra nuclear transport of the corresponding secondaries to the respective classes The design is a complex variant of a Strategy The most spectacular application of this pattern is the use of parton string models for string excitation quark molecular dynamics for correlated string decay and quantum molecular dynamics for transport a combination which promises to result in a coherent description of quark gluon plasma in high energy nucleus nucleus interactions The class G4VIntranuclearTransportModel provides registering mechanisms for concrete implementations of G4VPreCompou
132. s are automatically thread shared No action is needed however access to the data fields is in general thread unsafe and the same comments and recommendations for Case A are valid 2 14 3 2 8 Case H thread shared class instance s thread local and instance local data field This is the most complex case and it is relatively common in Geant4 Version 10 0 For example G4ParticleDefinition instances are shared among the threads but the G4ProcessManager pointer data field needs to be thread and instance local To obtain thread safe code two possible solutions exist Use the split class mechanism This requires some deep understanding of Geant4 multi threading and coordination with the kernel developers Split classes result in thread safe code with good CPU performance however they also require modification in other aspects of the kernel category in particular the run category The idea behind the split class mechanism is that each thread shared instance of G4Class initializes the thread local data fields by copying the initial status from the equivalent instance of the master which is guaranteed to be fully configured Additional details on split classes are available in a dedicated section An important side effect of the split class mechanism is that exactly the same number of instances of G4Class must exist in each thread e g the full set of G4Particles owned by the master is shared by threads If a new particle is created this has to be
133. s particularly dangerous and difficult to debug A classical way to solve the data race problem is to protect the critical section of the code and the concurrent access to a shared memory location using a lock or a mutex see section Threading model utilities and functions However this technique can reduce overall performance because only one thread at a time is allowed to be executed It is important to reduce to a minimum the use of locks and mutexes especially in the event loop In Geant4 we have achieved thread safety via the use of thread local storage This allows for virtually lock free code at the price of an increased memory footprint and a small CPU penalty Explanations of thread local storage are provided by several external resources For a very simple introduction but adequate for our discussion web resources give sufficient detail e g wikipedia Before going into the details of how to use the thread local storage mechanism we need to introduce some terminology We define an instance of a variable to be thread local or thread private if each thread owns a copy of the variable A thread shared variable on the contrary is an instance of a variable that is shared among the threads i e all threads have access to the same memory location holding the value of the variable If we need to share the same memory location containing the value of fValue between several instances of G4Class we call the data field instance shared otherwise
134. sition starting point of a step the track sees the same cross section at all positions in the volume The occurence biasing consists in substituting p by some arbitrary biased interaction law pp 3 6 3 1 Formalism for occurence biasing More details about the formalism will be provided in the physics reference manual biasing related part to come An arbitrary interaction law pp can be recasted in term of an effective cross section ob which depends on in general as P gb expl f ob S s where the integration runs over 0 e where gp is given by gp pof Priv e where Pny p is the probability for non interaction along segment 0 4 and is given by Pyr b 1 Hpy s ds exp Jov s ds where the integration runs over 0 which is the formalism that corresponds to non constant cross sections 66 Extending Toolkit Functionality When applying this formalism to the analog pdf p we simply have ob ga and Pu p H exp gai as this must In contrast with the analog case the effective cross section may depend on even in a volume made of single material An example of this is the forced interaction if it is decided that the interaction of a process with analog cross section ga will be forced and will happen somewhere on the segment 0 L then we have Forced interaction over segment 0 L case pol gaexpCgaft 1T expCgaL Pnip 1 exp gatt 1 exp ga
135. t V E Gavsolia Hecotatic gt gt Ge from GiLogicalvolume Bpishepeame Gistring S lt catation gt ne er a lt lt virtual gt gt CalculateE lt lt virtual gt gt DistanceTo lt cvirtual gt gt DistanceTo lt lt virtual gt gt Inside Scvirtual gt gt Surtacetior yy foaughters G4VTouchable lid G cscsolid pm from solids a X G snartVoxeltieadel G4AssemblyVolune GABOx caTubs f from solids from solids addPlacedvolume n E Sciassenblyvolume G pvPlacenent emm pom Suskeinprint E ScaPvPlace Figure 2 11 Overview of the geometry 2 7 3 Additional Geometry Diagrams Additional diagrams for the object oriented design of the geometry related classes are included here Figure 2 12 shows the class diagram for smart voxels Figure 2 13 shows the class diagram for the navigator G4SmartVoxelProxy G4smartVoxelProxy cetHeader HGetNode IsHeader Voxel Header is passed G4VoxelLimits during construction to provide G4SmartVoxelNode 0 Pisnode information on limits of fcontents G4SliceVe fNod 1 any previous axes 7 cetMaxEquivalentSlice tom GetMinEquivalentSlice fHeader I GetNoContained j 2 ed cetVvolume bInsert fcontents if 1 1
136. tates in his simulation An environment variable must be set by the user to activate such a simulation To improve performance ground states and long lived excited states are prepared at initialization time and loaded into the 52 Extending Toolkit Functionality kernel G4NuclideTable controls the half life threshold of these preloaded states The default value of the threshold is 1 microsecond and users may modify this value If users want to make the value shorter than 1 nanosecond then he must set the environment variable before Isomer levels G4NuclideTable provides an integer that represents the isomer level of each state Due to PDG code limitations only level numbers from 0 to 9 are allowed All ground states have a level number of 0 lowest energy state isomers have level number 1 next lowest have level number 2 and so on This continues up to level 8 All excited states above this will have level number 9 This numbering scheme is used only for the preloaded states In general the isomer level number for certain excited states depends on the half life threshold for preloaded states All excited states dynamically generated within the event loop will have 9 as its isomer level Adding states Users are able to add states to the table with specific values of excitation energy decay constant spin and dipole magnetic moment This should be done at initialization time and then user defined states will be preloaded However they alwa
137. tation is necessary They also show how to distinguish between permanent and transient objects see also Section Section 3 7 1 6 e GAXXXSG GAXXXSGSceneHandler G4XXXSGViewer Templates for a sophisticated graphics driver with a scene graph The scene graph following Open Inventor parlance is a tree of objects that dictates the order in which the objects are rendered It obviously lends itself to the rendering of the Geant4 geometry hierarchy For example the Open Inventor driver draws only the top level volumes unless made invisible by picking Thus the user can unwrap a branch of the geometry level by level This has performance benefits and gives the user significant and useful control over the view These classes show how to make a scene graph of drawn volumes 1 e the set of volumes that have not been culled Normally volumes marked invisible are culled 1 e not drawn Also the user may wish to limit the number of drawn volumes for performance reasons The drivers also have to process non geometry items and distinguish between transient and permanent objects as above 3 7 1 2 Important Command Actions To help understand how the Geant4 Visualization System works here are a few important function invocation sequences that follow user commands For an explanation of the commands themselves see command guidance or the Control section of the Application Developers Guide For a fuller explanation of the functions see appropriate base cl
138. tector s instance of this field So documenting what each component means is required to give them the necessary information For example someone can describe DetectorAbc s field by creating a class DetectorAbcField that derives from your NewField class DetectorAbcField public NewField public void MyFieldGradient GetFieldValue const double Point 3 double pField They then implement the function GetField Value void MyFieldGradient GetFieldValue const double Point 3 double pField We expect pField to point to pField 9 This amp the order of the components of pField is your own convention We calculate the value of pField at Point A new Equation of Motion for the new Field Once you have created a new type of field you must create an Equation of Motion for this Field This is required in order to obtain the force that a particle feels 49 Extending Toolkit Functionality To do this you must inherit from G4Mag EqRhs and create your own equation of motion that understands your field In it you must implement the virtual function EvaluateRhsGivenB Given the value of the field this function calculates the value of the generalised force This is the only function that a subclass must define virtual void EvaluateRhsGivenB const G4double yl const G4double B 3 G4double dydx const 0 In particular the derivative vector dydx is a vector with six components The first three are
139. ter space by overlaying cross section data sets to optimise the overall result Examples are the cross sections for low energy neutron transport If these are registered last by the user they will be used whenever low energy neutrons are encountered In all other conditions the system falls back on the default or data sets with earlier registration dates The fact that the registration is done through abstract base classes with no side effects allows the user to implement and use his own cross sections Examples are special reaction cross sections of Ke nuclear interactions that might be used for analysis at LHC to control the systematic error Final state production The G4HadronicProcess class provides a registration service for classes deriving from G4Hadronic Interaction and delegates final state production to the applicable model G4Hadronic Interact ionprovides the functionality needed to define and enforce the applicability of a particular model Models inheriting from G4Hadronic Interaction can be restricted in applicability in projectile type and energy and can be activated deactivated for individual materials and elements This allows a user to use final state production models in arbitrary combinations and to write his own models for final state production The design is a variant of a Chain of Responsibility An example would be the likely CMS scenario the combination of low energy neutron transport with a quantum molecular dynamics
140. the accuracy required i e the number of points where the function pFunction will be evaluated during integration The function creates the arrays for abscissas and weights that used in Gauss Legendre quadrature method The values a and b are the limits of integration of the function f nLegendre MUST BE EVEN Returns the integral of the function f between a and b by 2 fNumber point Gauss Legendre integration the function is evaluated exactly 2 fNumber times at interior points in the range of integration Since the weights and abscissas are in this case symmetric around the midpoint of the range of integration there are actually only fNumber distinct values of each Convenient for using with some class object dataT template class T class F gt G4double G4Integrator T F Legendrel0 T typeT F f G4double a G4double b 4f Returns the integral of the function to be pointed by T f between a and b by ten point Gauss Legendre integration the function is evaluated exactly ten times at interior points in the range of integration Since the weights and abscissas are in this case symmetric around the midpoint of the range of integration there are actually only five distinct values of each Convenient for using with class object typeT The method is very fast and accurate enough Roots and weights are from Abramowitz M Stegan I A 1964 Handbook of Math p 916 te
141. the derivative of the position with respect to the curve length Thus they should set equal to the normalised velocity which is components 3 4 and 5 of y dydx 0 dydx 1 dydx 2 y 31 y 4 vyl51 The next three components are the derivatives of the velocity vector with respect to the path length So you should write the force components for dydx 3 dydx 4 and dydx 5 for your field Get a G4FieldManager to use your field In order to inform the Geant4 system that you want it to use your field as the global field you must do the following steps 1 Create a Stepper of your choice yourStepper new G4ClassicalRK yourEquationOfMotion or if your field is not smooth eg A new G4ImplicitEuler yourEquationOfMotion 2 Create a chord finder that uses your Field and Stepper You must also give it a minimum step size below which it does not make sense to attempt to integrate yourChordFinder new G4ChordFinder yourField yourMininumStep say 0 01 mm yourStepper 3 Next create a G4FieldManager and give it that chord finder yourFieldManager new G4FieldManager yourFieldManager SetChordFinder yourChordFinder 4 Finally we tell the Geometry that this FieldManager is responsible for creating a field for the detector G4TransportationManager GetTransportationManager SetFieldManager yourFieldManager Changes for non electromagnetic fields If the field you are interested in simulating
142. the number of excitons in the system equals the mean number of excitons expected in equilibrium for the current excitation energy Then it hands over to the evaporation phase The evaporation phase decays the residual nucleus and the Chain of Command rolls back to GATheoFS Generator accumulating the information produced in the various levels of delegation 3 5 6 Level 4 Frameworks String Parton Models and Intra Nuclear Cascade lt lt Abstract gt gt G4VPartonStringModel HsScatter lt lt Purely Abstract c tWoundedNucli ji i G4VStringFragmentation niti o Ml tl G4ExcitedString FragmentString 1 1 c lt virtual gt gt GetStrings IN J Sf CorrectHadronMomenta qf SetThisPointer lt lt Concrete gt gt o i lt lt Concrete gt gt G4PythiaFragmentationInterface pue G4QuarkGluonStringModel G4FTFModel GetStrings lt lt Concrete gt gt HGetWoundedNucleus HGetWoundedNucleus G4LongitudinalStringDecay ao Ps SPExciteParticipants reateSoftString uildStrings tring iaussianPt hooseX Figure 3 6 Level 4 implementation framework of the hadronic category of Geant4 parton string aspect Purely Abstract G4VintraNuclearTransportModel SApplyYourself G4VKineticNucleon Propagate Decay GetdMomentum GetDefinition GetPosition G4V3DNucleus Pinit T Concrete AgetCharge neo ietMassNumber G4HadronKineticModel GetMass couNucicon
143. the simulation depending on the conditions at the point of interaction Ability to add user defined isotope production models in a seamless manner Design and interfaces The above requirements are implemented in three framework components one for cross sections final state production and isotope production each The class diagrams are shown in Figure 3 2 for the cross section aspects Figure 3 3 for the final state production aspects and figure Figure 3 4 for the isotope production aspects lt lt Abstract gt gt G4HadronicProcess Hx lt virtuab gt GetMicroscopicCrossSection lt virtual gt gt PostStepDolt S RegisterMe S ChooseHadronicinteraction GeneralPostStepDolt Hx lt static gt gt GetlsotopeProductioninfo RegisterlsotopeProductionModel lt static gt gt EnablelsotopeProductionGlobally Hx lt static gt gt DisablelsotopeProductionGlobally nablelsotopeCounting HDisablelsotopeCounting lt lt Concrete gt gt lt lt Concrete gt gt lt lt Concrete gt gt lt lt Concrete gt gt G4HadronFissionProcess G4HadronlnelasticProcess G4HadronElasticProcess G4HadronCaptureProcess jl Concrete r G4CrossSectionDataStore AddDataSet HGetCrossSection lt lt Concrete gt gt 0 ADataSet Purely Abstract gt gt G4VCrossSectionDataSet HlsApplicable GetCrossSection lt lt Concrete gt gt BDataSet Figure 3 2 Level 2 implementation frame
144. the step length through one of its three GetPhysicalInteractionLength methods AtRest AlongStep or PostStep Second for the selected processes the Dolt AtRest AlongStep or PostStep methods are invoked All this interaction is managed by the Stepping method of G4SteppingManager To calculate the step length the DefinePhysicalStepLength method is called The flow of this method is the following Obtain maximum allowed Step in the volume define by the user through G4UserLimits The PostStepGetPhysicalInteractionLength of all active processes is called Each process returns a step length and the minimum one is chosen This method also returns a G4ForceCondition flag to indicate if the process is forced or not Forced Corresponding PostStepDolt is forced NotForced Corresponding PostStepDolt is not forced unless this process limits the step Conditionally Only when AlongStepDolt limits the step corresponding PoststepDolt is invoked ExclusivelyForced Corresponding PostStepDolt is exclusively forced All other Dolt including AlongStepDolts are ignored The AlongStepGetPhysicalInteractionLength method of all active processes is called Each process returns a step length and the minimum of these is chosen This method also returns a fGPILSelection flag to indicate if the process is the selected one can be is forced or not CandidateForSelection this process can be the winner If its step length is the smallest it will
145. these methods When implementing ApplyYourself the Get methods of the G4HadProjectile and G4Nucleus classes provide all the initial state information necessary for the generation of the final state For G4HadProjectile GetDefinition provides the particle type and Get4Momentum provides the total energy and momentum For G4Nucleus GetZ_asInt GetN asInt and GetA_asInt provide Z N and A while AtomicMass provides the mass Additional utility methods are available for both G4HadProjectile and G4Nucleus Coordinate systems The inputs to the model assume that the incident particle G4HadProjectile travels along the z axis and interacts with the target G4Nucleus which is at rest in the lab frame Before invoking the ApplyYourself method the process rotates the direction of the projectile to be along the z axis and then performs the inverse rotation on the final state particles produced by the model The model must perform two additional transformations into the CM frame and back out of it after the interaction is complete 62 Extending Toolkit Functionality Writing the ApplyYourself method It is thus the model developer s responsibility to boost the projectile and target into the CM frame using the necessary Lorentz transformations perform all calculations required to generate the final state set of particles boost the final state particles back to the lab frame with the inverse transformation and e s
146. trategy The class diagram is shown in Figure 3 8 At this point in time the usage of the G4AVFragmentation Function is not enforced by design but made available from the G4VString Fragmentation to an implementer of a concrete string decay G4VString Fragmentation provides a registering mechanism for the concrete fragmentation function It delegates the calculation of z of the hadron to split of the string to the concrete implementation Standardisation in this area is expected 3 5 8 Creating Your Own Hadronic Process For some applications Geant4 might not provide the most appropriate physics implementantion or in fact any physics implementation at all In such cases it is up to the user to develop the necessary processes models and cross sections and integrate them into his version of the Geant4 toolkit The user s process model or cross section may then be used in a physics list to replace some of those already provided by the toolkit This modularity requires that user classes be derived from a set of base classes which have been provided to aid integration with the toolkit and to spare the user from consideration of many details not related to the physics at hand Processes communicate with Geant4 tracking telling it where or when an interaction is supposed to occur and what is supposed to happen at that point A hadronic process may be implemented directly or through the use af a framework of classes that modularize physics functionality
147. tsColle 4 GAVHit ans calorimeterHi y ctionArray cram tsColeciong i print Ve a RWTValOrderedVe QE og ctor ok irom RogueWave phamber calorimeter calorimeterHi A bra scm chamberHitsColieci chamberHit i agma onArray Choice out of these two kinds of vectors G4Allocator RWTPtrOrderedVe tom Glooals cior from RogueWave 3 e counterHitsCollection _ counterHilsCalleciio counter counterHit o H uu AY e vw OW Fi 2 hit cl igure 2 9 User hit classes G4VSensitiveDe tector o 1 0 1 G4VReadOutG eometry E build includelist 1 e e 1 e excludeList 0 n m G4GRSVolume 1 HORS VETEN G4SensitiveVol from Geometry umeList 0 n checkLV chock PNG G4GRSSolid G4VPhysical o n o from Geometry Volume from Geometry em On G4LogicalVol a G4VTouchable ume from Geometry Figure 2 10 Readout geometry 13 from Geometry y Design and Function of Geant4 Categories Status of this chapter 27 06 05 section on design philosophy added from Geant4 general paper by D H Wright Dec 2006 Conversion from latex to Docbook verson by K Amako 2 7 Geometry 2 7 1 Design Philosopy The geometry category provides the ability to describe a geometrical structure and propagate particles efficiently through it This is done in part with the aid of two central concepts the logical and physical volumes A logical volume represents a detector element of a given shape which may contain other vo
148. ty the kernel perhaps because the view parameters have changed drastically this should be done in the concrete viewer s DrawView if fNeedKernelVisit fSceneHandler ProcessScene this fNeedKernelVisit false 3 7 1 5 What happens in ProcessScene ProcessScene is inherited from G4VSceneHandler It causes a traversal of the run duration models in the scene For drivers with graphical databases it causes a rebuild ClearStore Then for the run duration models fReadyForTransients false BeginModeling for each run duration model pModel DescribeYourselfTo this EndModeling fReadyForTransients true A second pass is made on request see G4VSceneHandler ProcessScene The use of fReadyForTransients is described in Section 3 7 1 6 What happens then depends on the type of model G AxesModel G4AxesModel DescribeYourselfTo simply calls sceneHandler AddPrimitive methods directly SceneHandler BeginPrimitives SceneHandler AddPrimitive x axis etc SceneHandler EndPrimitives Most other models are like this except for the following e G4PhysicalVolumeModel The geometry is descended recursively culling policy is enacted and for each accepted and possibly clipped solid SceneHandler PreAddSolid theAT pVisAttribs pSol DescribeYourselfTo sceneHandler 1 For example if pSol points to a G4BOX gt G4Box DescribeYourselfTo G4VGraphicsScene amp s
149. unctionalities Extending the Navigator The main responsibilities of the Navigator are locate a point in the tree of the geometrical volumes compute the length a particle can travel from a point in a certain direction before encountering a volume boundary The Navigator utilises one helper class for each type of physical volume that exists You will have to reuse the helper classes provided in the base Navigator or create new ones for the new type of physical volume To extend G4Navigator you will have then to inherit from it and modify these functions in your ModifiedNavigator to request the answers for your new physical volume type from the new helper class The ModifiedNavigator should delegate other cases to the Geant4 s standard Navigator Replacing the Navigator Replacing the Navigator is another possible operation It is similar to extending the Navigator in that any types of physical volume that will be allowed must be handled by it The same functionality is required as described in the previous section However the amount of work is probably potentially larger if support for all the current types of physical volumes is required 48 Extending Toolkit Functionality The Navigator utilises one helper class for each type of physical volume that exists These could also potentially be replaced allowing a simpler way to create a new navigation system 3 2 Electromagnetic Fields 3 2 1 Creating a New Type of Field
150. up the logic of a specific biasing technique It is messaged 65 Extending Toolkit Functionality by each G4BiasingProcessInterface callingProcess instance which pass their identity through their own pointer values The operator has hence all the necessary information for taking decisions In addition since 10 1 the G4BiasingProcessInterface callingProcess instances do anticipated calls to their underneath wrapped physics process if any the first of the G4BiasingProcessInterface callingProcess instance trigger calls to all PostStepGetPhysicallnteractionLength methods of biased processes In this way all process cross sections have been updated before the first call to the biasing operator This one has hence all ready to use physics information the first it is messaged in the step by the first G4BiasingProcessInterface callingProcess instance The G4VBiasingOperator class defines the following interface e virtual G4VBiasingOperation ProposeNonPhysicsBiasingOperation const G4Track track const G4BiasingProcessInterface callingProcess 0 This method is called by each G4BiasingProcessInterface instance which does not hold wrap a physics process The G4VBiasingOperation returned will have its DistanceToApplyOperation and GenerateBiasingFinalState methods called at proper times post step GPIL and post step Dolt times respectively by the G4BiasingProcessInterface callingProcess virtual G4VBiasingOper
151. use For example do not use a single G4Cache for several data fields instead use a helper structure as the template parameter for G4Cache 40 Design and Function of Geant4 Categories class Elclass 1 SRC G4double fValuel G4Something fValue2 FoToBeCached t G4Cache ToBeCached t fCache Two specialized versions of G4Cache exist that implement the semantics of std vector and std map G4VectorCache lt T gt implements a thread local std vector lt T gt with methods Push_back operator Begin End Clear Size and Pop back G4MapCache lt K V gt implements a thread local std map lt K V gt with methods Insert Begin End Find Size Get Erase operator and introduces the method Has A detailed example of the use of these cache classes is discussed in the unit test source global management test testG4Cache cc 2 14 3 4 2 G4AutoDelete namespace During the discussion of G4Cache we have shown the example of storing a pointer to a dynamically created object A common problem is to correctly delete this object at the end of its life cycle Since the G4Class instance is thread shared it is not possible to delete the cached object in the destructor of G4Class because it is called by the master and the thread local instances of the cached object will not be deleted In some cases to solve this problem it is possible to use a helper introduced in the namespace G4AutoDelete
152. w EM physics needs to be created only new model class may be created and existing EM process class may be reused A new model may be added to the existing process using AddEmModel G4int G4VEmModel G4Region method Status of this chapter 27 06 05 under construction Dec 2006 Conversion from latex to Docbook verson by K Amako Dec 2014 V Ivanchenko added description 3 5 Hadronic Physics 3 5 1 Introduction Optimal exploitation of hadronic final states played a key role in successes of all recent collider experiment in HEP and the ability to use hadronic final states will continue to be one of the decisive issues during the analysis phase of the LHC experiments Monte Carlo programs like Geant4 facilitate the use of hadronic final states and have been developed for many years We give an overview of the Object Oriented frameworks for hadronic generators in Geant4 and illustrate the physics models underlying hadronic shower simulation on examples including the three basic types of modeling data driven parametrisation driven and theory driven modeling and their possible realisations in the Object Oriented component system of Geant4 We put particular focus on the level of extendibility that can and has been achieved by our Russian dolls approach to Object Oriented design and the role and importance of the frameworks in a component system 3 5 2 Principal Considerations The purpose of this section is to explain the imple
153. work of the hadronic category of Geant4 cross section aspect lt lt Abstract gt gt G4HadronicProcess lt lt virtual gt gt GetMicroscopicCrossSection H lt lt virtual gt gt PostStepDolt S RegisterMe hooseHadronicinteraction GeneralPostStepDolt lt lt static gt gt GetlsotopeProductioninfo S RegisterlsotopeProductionModel lt lt static gt gt EnablelsotopeProductionGlobally lt cstatic gt gt DisablelsotopeProductionGlobally VEnablelsotopeCounting DisablelsotopeCounting lt lt Concrete gt gt 9 1 G4EnergyRangeManager seAbstaepo 1 64Hadroniclnteraction o G4Element j GetHadronicinteraction ApplyYourself SetMinEnergy 0 AGetMaxEnergy DeActivateFor G4Material lt lt Concrete gt gt LL ConcreteModel Figure 3 3 Level 2 implementation framework of the hadronic category of Geant4 final state production aspect 56 Extending Toolkit Functionality lt lt Abstract gt gt G4HadronicProcess lt lt virtual gt gt GetMicroscopicCrossSection lt virtual gt gt PostStepDolt S RegisterMe hooseHadronicInteraction GeneralPostStepDolt lt lt static gt gt GetlsotopeProductionInfo S RegisterlsotopeProductionModel H lt lt static gt gt EnablelsotopeProductionGlobally lt lt static gt gt DisablelsotopeProductionGlobally S EnablelsotopeCounting DisablelsotopeCounting 0 incri 3
154. y a change of model view matrix whilst a change of rendering mode from wireframe to surface might require a rebuild of the graphical database A rebuild of the run duration persistent objects in the scene is called a kernel visit the viewer prints Traversing scene data Note that end of event transient objects are only rebuilt at the end of an event or run under control of the visualisation manager Smart scene handlers keep them in separate display lists so that they can be rebuilt separately from the run duration objects see Section 3 7 1 6 Integrated viewers with no graphical database For example G4OpenGLImmediateXViewer DrawView NeedKernelVisit Always need to visit G4 kernel ProcessView FinishView Integrated viewers with graphical database For example GAOpenGLStoredXViewer DrawView KernelVisitDecision Private function containing if significant change of view parameters NeedKernelVisit ProcessView FinishView e File writing viewers For example G4ADAWNFILEViewer DrawView NeedKernelVisit ProcessView Note that viewers needing to invoke FinishView must do it in DrawView 3 7 1 4 What happens in ProcessView ProcessView is inherited from G4VViewer void G4VViewer ProcessView If ClearStore has been requested e g if the scene has changed of if the concrete viewer has decided that it necessary to visit Extending Toolkit Functionali
155. ys have an isomer level of 9 and neglect the numbering of isomer levels of other states Currently G4RadioactiveDecay and G4PhotoEvporation models share the state information with G4NuclideTable Other models are encouraged to follow these Status of this chapter Nov 2008 created by H Kurashige Dec 2013 G4NuclideTable added by T Koi Jan 2014 spelling and grammar revision by D H Wright 3 4 Electromagnetic Physics Electromagnetic EM processes of Geant4 following base interfaces G4VEnergyLossProcess G4VEmProcess G4VMultipleScattering These base classes providing all management work of initialisation of process creation and filling of physics tables generic run time actions Concrete process classes are responsible for initialisation of parameters and defining of set of models for the process A list of example of EM processes G4PhotoelectricEffect G ComptonScattering G GammaConversion G GammaConversion e G4RayleighScattering e G4elonisation G4eBremsstrahlung e G4hlonisation G4Mulonisation e G4hlonisation e G4MuBremsstrahlung G4eMultipleScattering G4MuMultipleScattering and others In some specific cases these interfaces are not applicable and high level interface G4VProcess is used Concrete physics models are implemented via EM model interfaces G4VEmModel 53 Extending Toolkit Functionality G4VMscModel In majority of use cases when ne

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