SIMSCRIPT II.5 Simplified
Contents
1. Russell 1983 Nor do the notes show how to compile and run programs The first section is treated as a general purpose computer language It has all the programming structures that we are used to seeing in computer languages and it can be used for normal calculations just like Pascal Java or Python The second section describes the special additions that make into a simulation language These include simulation time processes and resources In the third section the statistical routines used for generating random numbers and for monitoring simulations are described briefly SIMSCRIPT II 5 Simplified 2 Simscript lI 5 Language Elements SIMSCRIPT II 5 is a computer language with all the usual elements 2 1 Program Structure Every program must have a main program In addition it may contain a preamble and a number of routines main program Every program must contain one main program which is the main processing part preamble This contains all global declarations It is not always required If it is included it must be listed before the main program routines Such as Functions Subroutines Events and Processes These are not always required but will be needed in simulation programs 2 2 The Main Program The main program starts with the word main All blocks finish with end Example 2 1 From time immemorial the first program that learners write is the one that prints out Hello World Here it is in SIMSC2. SIMSCRIPT IL5 Simplified CACI SIMSCRIPT II 5 Simplified This document was produced by Professor Tony Vignaux Victoria University New Zealand Tony Vignaux mcs vuw ac nz Updated November 2002 by CACI If there are questions regarding the use or availability of SIMSCRIPT II 5 product please contact CACI at any of the following addresses For product Information contact CACI Products Company CACI Worldwide Headquarters 1011 Camino Del Rio South suite 230 1100 North Glebe Road San Diego California 92108 Arlington Virginia 22201 Telephone 619 542 5224 Telephone 703 841 7800 www caciasl com www caci com For technical support contact Manager of Technical Support CACI Products Company 1011 Camino Del Rio South 230 San Diego CA 92108 Telephone 619 542 5224 simscript caci com The information in this publication is believed to be accurate in all respects However CACI cannot assume the responsibility for any consequences resulting from the use thereof The information contained herein is subject to change Revisions to this publication or new editions of it may be issued to incorporate such change SIMSCRIPT 11 5 is a registered trademark and service mark of CACI Products Company TABLE OF CONTENTS I Hr OGUCCIOU LL cutus ose toten tena eid eei 1 2 Simscript II 5 Language Elements 3 2 1 Program SU IU up CE 3 2 2 Whe Maiti Prora Louie tiet pata Pr Y vs
3. here Some automatically generated attributes routines and variables Entities variable entity global variable variable N entity 7 of entities n class only permanent entities i i l try ti f Processes attribute mea Tex scheduled entry time for the process t of iting for thi resource o let resource set of processes using this resource attribute U resource number of idle units Sets attributes F set first entity in set of owner L set last entity in set entities N set number of entities in set Sets attributes P set pointer to predecessor in set 25 SIMSCRIPT II 5 Simplified of member S set pointer to successor in set o exis Mex equals 1 if entity is in the set 0 otherwise Thus the processes waiting for a resource R are listed in the set Q R and the variable N Q R tells you how many there are To list them you would start at F Q R which is the first one waiting If First one F Q R the next one waiting is S First one the successor to the first one 26 4 Statistical Aspects of Simulation SIMSCRIPT II 5 provides a number of statistical facilities These include random variate generation with different seed streams and statistical monitoring methods See CACD 1997 Section 5 3 4 1 Random Number Generation There are 10 random number streams numbered S 1 10 At any instant each stream has an integer seed value which is updated every time the stream is called on for a random
4. ke Pay Ee cuin 0 k z n eh c na sote RMN D k d k ke N e 3 2 3 VaEIDIM S uices pad eter Eke kek Kawa NA EE NARA V R Re B Fek di a Z NA WE W WA VE E Dna keh awa KENA DAS 4 2 3 do MOQd Suya Hen Me atan in A WAA Gots ENA OA tct ue 4 2 3 2 Local and Global Variables iEEEEEE 5 2 9 9 SATA VS ocn EE dek n y E Dun dinek ke ME An eee eb Aud ped 5 2 4 The Preamble C 5 2 5 The Assignment Statemenmt s ess esssecosecssecesecesecesese sese 6 2 6 Input and O Ut b 4i 1i 5444 44 2y5 5 soksse eed ae o erre cob ewe e000 pue Rae PEST CE SWE XR REREKER CR ERG 6 2 6 1 Free form Input read 6 2 6 2 Quick and dirty output list sss 6 2 6 3 Output with a Template print 7 Dak Program ELO WS uekandedic escis eetebeeses oo 0054000404 aie bk 9540 0005 kik 584 ey b ava Na M GE W N 8 2 1 Selector Phrases use goto SEA CORO Nes a a 8 2 8 IRO T DIT GS ETE 2 HE E Hena V RA RU HEE a Ve KE K N QU E he we Kun C R A kO KE k nA WE WE EN eke kE WA WA V UU 9 29 15 PATQUMENIS 4 ee KARA NA ERK bali bue s ayak Aa 9 2 8 2 FUNCIONS euet ete dot tee bet oU quiis 10 2 9 Predefined El ments depo i We K i Ka E A We Va s ku k A beo d k K ea uu cek s bek 11 3 Simu
5. kindly corrected a number of mistakes and suggested changes I will be grateful for any corrections or suggestions for improvements to the document from students experts or anyone accessing it over the Web My email address is Tony Vignaux vuw ac nz 5 1 References CACI83 1997 CACI83 1997 SIMSCRIPT 77 5 Reference Handbook C A C I 2nd edition CACI89 1989 CACI89 1989 UNIX SIMSCRIPT II 5 User s Manual C A C I Law and Larmey 1984 Law A M and Larmey C S 1984 An Introduction to Simulation using SIMSCRIPT 11 5 C A C I CACI97 1997 CACI97 1997 SIMSCRIPT 5 Programming Language C A C I Pidd 1992 Pidd M editor 1992 Computer Simulation in Management Science Wiley 3rd edition Russell 1983 Russell E C 1983 Building Models with SIMSCRIPT II 5 C A C I 5 1 1 Footnotes 1 II 5 disregards all periods written at the end of names and numbers Thus the names flight and flight become flight when the program is compiled SIMSCRIPT II 5 Reference Manual You can have periods within an identifier In the word mode is used instead of type Don t read this If a name is not explicitly declared will declare it implicitly with double mode Implicit declaration is strongly discouraged because it can lead to errors that are hard detect We forbid this using a command in the preamble see the beginning of Section 2 4 SIMSCRIPT II 5 Simplified Arrays can b
6. least one event The start simulation will make the programme jump to that event When the simulation ends the Report routine is called main call Initialise activate a PoissonProcess now start simulation call Report end main SIMSCRIPT II 5 Simplified 3 2 Entities Before we look at processes we must look briefly at entities An entity is an element of the system being simulated that can be individually identified and processed In they can be either permanent or temporary They are defined in the preamble using either an include or an every declaration statement every statements will be dealt with in Section 3 2 2 Example 3 2 Defining some entities preamble normally mode is undefined permanent entities include Teller Computer temporary entities include customer Task end preamble We will not say much about permanent entities in this simplified version of the language though they will be used in the form of resources see Section 3 5 3 2 1 Creating and using Temporary Entities Temporary entities must not only be defined in the preamble they must be created before they can be used Example 3 3 Assuming that the customer has been defined as a temporary entity we can create it as follows create a customer When a temporary entity say customer is created e a section of memory is allocated to hold its attribute values see section 3 2 2 to find out what attributes are and e asingle global variable cust
7. name must be that of the process defined in the preamble The process starts executing the routine when it is activated Example 3 12 A process routine for a ticking clock int is the time interval between ticks It would be defined as an attribute of the process entity and an argument of the process routine process clock int define int as a double variable define 1 as an integer variable fori 1 to 10 do print line with time v thus wait int units loop end clock 3 4 3 Creating a Process Entity A new process entity appears when the process is created or activated To create and start a new process in one step use the activate statement Pointer variables can be used to reference such new processes Example 3 13 We activate two messages immediately the word a indicates that we are both creating and activating new messages they have no attributes The word now implies no simulation delay before the process starts activate a message now activate a message called mmm now 18 Simulation with SIMSCRIPT II 5 It is also possible to give values to the attributes of the process before it is activated This is done by first creating it setting the attribute values and then activating it Example 3 14 Here the customer is created first given an attribute value then activated The word the is used to indicate we are not creating a new customer when we activate The attribute cu Arrival time here records the time the customer is
8. 0 do wait exponential f Mean 1 units activate a customer i now add 1 to count arrivals loop end Arrival Generator process customer id define id as an integer variable print 1 line with time v and id thus soe KE customer arrives wait exponential f sojourn 2 units print 1 line with time v and id thus se kk customer departs add 1 to count departs end customer process Close Doors interrupt Arrival Generator 22 call Report stop end Close Doors routine Read Data read Day Length Mean and sojourn end Read Data routine Report print 2 line with count arrivals and count departs thus customers arrived customers departed end Report Simulation with SIMSCRIPT II 5 Example 3 27 An example of the trace output from a run of this program is as follows 078 customer 1 803 customer 3 219 customer 3 242 customer 3 619 customer 4 643 customer 4 803 customer 5 146 customer 5 222 customer 5 404 customer 5 654 customer 5 847 customer 6 315 customer 6 860 customer 7 285 customer 7 765 customer 7 882 customer arrives 2 arrives 3 arrives 4 arrives 3 departs 5 arrives 6 arrives 1 departs 7 arrives 8 arrives 8 departs 7 departs 9 arrives 2 departs 6 departs 10 arrives 9 departs 10 customers arrived 7 customers departed 3 5 Resources A resource models a congestion point where there may be queuing For example in a manufacturing plant a Task modeled as a proc
9. Ambulance now loop end routine Initialise Routines are executed using the call statement For example Example 2 16 Executing a routine using a call statement call Initialise 2 8 1 Arguments Routines can be given arguments and return results The arguments supplying data are separated from those returning the result This is done using the keywords given and yielding Arguments behave like local variables and their mode must be declared immediately after the routine heading As they are local to the routine they can be given any names you like Example 2 17 This routine calculates the value of Profit given the amount of Production routine Profit Calc given Production yielding Profit define Production Profit as double variables arguments define Fixed Contribution as double variables local SIMSCRIPT II 5 Simplified let Fixed 10000 0 let Contribution 20 0 let Profit Fixed Contribution Production end Profit Calc Example 2 18 The above routine would be called like this call Profit Calc given 50000 0 yielding The Profit Instead of given you can enclose the given arguments in parentheses Convention We usually declare and call routines with a list of given arguments enclosed in parentheses You don t need the word given then Example 2 19 For example the above definition could be written routine Profit Calc Production yielding Profit define Production Profit as double variables lots of calc
10. Arrival time Fred 13 3 activate the customer called Fred now However a process attribute such as cu Arrival time and a process routine argument i 20 such as ArrTime cannot have the same name 19 SIMSCRIPT II 5 Simplified 3 4 5 Elapsing Time in a Process Within a process routine the process can wait or work for some time interval measured in units It can also request and relinquish resources as described later in Section 3 5 In this way it can simulate the elapsing of time Example 3 19 The process will hold for a random time with mean 10 0 units work exponential f 10 0 3 units wait and work are effectively synonymous but work is more appropriate if a resource is being used A process disappears when it is destroyed or when it runs off the end of its routine Convention we do not usually destroy processes instead allow them to run off the end of the routine 3 4 6 A Complete Program Using wait Commands Example 3 20 This program simulates a firework with a time fuse It contains a preamble to define the firework process I have put in a few extra wait commands preamble normally mode is undefined processes include firework end preamble main activate a firework in 20 0 units start simulation end main process firework define i as an integer variable print 1 line with time v thus sees ek firework activated wait 10 0 units fori 1 to 10 do wait 1 0 unit print 1 line with time v and i thus FO
11. EAM e uniform f Start Finish STREAM These routines contain calls to random f STREAM and use the corresponding seed stream Example 4 3 To generate a sample x from an exponential distribution with mean 20 0 using STREAM 1 one would use the following call Notice that I have been careful to put in a decimal point into the first argument which must be real x exponential f 20 0 1 NOTE You must use real values if a routine requires a real argument For example exponential f 3 1 will not give you a sample from an exponential with mean 3 Instead you must use the call exponential f 3 0 1 does NOT automatically convert arguments from integer to real 4 2 Statistical Monitoring Any global variable can be automatically monitored by the system to calculate statistics Little change has to be done to the program except by the addition of a special statement in the preamble The two types of monitoring are tally and accumulate 4 2 1 Tally tally takes a sample every time the variable is changed It is intended to monitor a number of individual observations such as waiting times Example 4 4 here in the preamble we define two global variables and then indicate that they are to be monitored using the tally statement The tally statement specifies that we want to find both the mean and standard deviation of the values of the waiting time preamble define Waiting time and Time in bank as real variables tally Avg Wait as th
12. Example 3 10 and taken out using the remove statement Line 7 in Example 3 10 The entities are filed in the appropriate order automatically Sets have a number of standard attributes automatically defined and updated for you see Section 3 6 A most useful one is the number of entities in the set For a set called Q the 16 Simulation with SIMSCRIPT II 5 number of entities it holds is N Q This is automatically updated whenever entities are added to or removed from the set You can test if a set is empty or not using the forms Q is empty or Q is not empty You can also ask if a particular entity say E is in the set using E is in Q or E is not in Q Example 3 10 following on from Problem 3 8 Here we create a Job100 and a Task which is put onto Job100s Task list The print statement 6 outputs the number in the Task list We can remove the task from the set 7 The particular statement used does not destroy the task and it can be accessed using tt 1 define Job100 and tt as pointer variables 2 create a Job called Job100 3 create a Task called tt 4 let Tk durationn tt 100 0 5 file tt in the Task list Job100 6 print 1 line with N Task list Job100 thus Number in task list is 7 remove the first tt from the Task list Job100 8 if the Task list Job100 is empty 9 print 1 line thus 10 Set is empty 11 12 endif 3 4 Processes We now come to the main tool for discrete event simulation A pro
13. IE ek tick loop wait 10 0 units print 1 line with time v thus Heri ae ria ek Boom end process firework The output from the program in Example 3 20 is 20 00 firework activated 31 00 tick 1 20 Simulation with SIMSCRIPT II 5 32 00 tick 2 33 00 tick 3 34 00 tick 4 35 00 tick 5 36 00 tick 6 37 00 tick 7 38 00 tick 8 39 00 tick 9 40 00 tick 10 50 00 Boom One useful program pattern is the generator See Example 3 21 This is a process that generated events or activates a number of other processes as a sequence it is a source or generator of other processes Random arrivals are generated using such a process Example 3 21 The generator pattern A process to generate a series of customers to arrive at intervals of 10 0 units of time To achieve random arrivals of customers the wait statement should use an exponential random variate instead of as here a constant 10 0 value process Generator while time v Finish time do activate a customer now wait 10 0 units loop end Generator 3 4 7 Interactions of Processes The various states that a process can exist in are shown in this diagram An executing process can suspend itself and can be sent a reactivate command by another process Example 3 22 The process itself would say suspend and some other process would reactivate using the form Example 3 23 reactivation by a second process reactivate the customer called Fred now 3 4 8 Interruptions A pen
14. Machine N Q Machine 1 the number of processes waiting X Machine 1 the set containing resources using units of a type 1 Machine N X Machine 1 the number of processes using units 24 Simulation with SIMSCRIPT II 5 3 5 1 Using Resources The process routines will contain statements to interact with the resource These are the request and the relinquish statements To use a resource for a time a process will request a number of units of the particular type If they are available they are allocated to the process which then holds them until releasing them If they are not available the processes will he held on the waiting queue until some come free The process will suspend its operation until it receives its request See Example 3 31 On finishing with the resource the process must release it using the relinquish statement saying how many units of what type are to be released ying y yp Example 3 31 Here the Job requests and if necessary waits for one unit of a Machine of type 2 On acquisition it then holds it while it works for a random time exponentially distributed mean 20 0 units and then relinquishes it again process Job request Machine 2 work exponential f 20 0 3 units relinquish 1 Machine 2 end Job 3 6 Standard Attributes Entities sets processes and resources have predefined standard attributes in addition to those defined by the user These are listed in the manuals Only a few are tabulated
15. RIPT 11 5 We now look at some of the special facilities provides for the simulation programmer They include entities sets processes resources and importantly ways of recording and elapsing simulation time 3 1 Simulation Time All discrete event simulation programs have the simulation time maintained in a software clock In this is called time v time v is a double variable It is sed to record and print out the current simulation time particularly in controlling the simulation and in producing traces of its operation Do not attempt to alter time v yourself A s s 13 Time is measured in units During the running of a simulation program time steps forward from one event to the next An event occurs whenever the state of the simulated system changes For example an arrival of a customer is an event So is a departure Execution of this timing mechanism does not start until the following statement appears in the main block of the program start simulation The simulation then starts the timer routine seeking the first scheduled event It continues to run until there are no further events to execute This 1s the usual method of ending a simulation More statements can be executed after the simulation like the call Report in Example 3 1 The program can be terminated using the stop statement Example 3 1 This shows only the main block in a simulation program Activating the PoissonProcess has the effect of scheduling at
16. RIPT II 5 It consists of just one main block main print 1 line thus Hello World end main Comments begin with two single quotes The rest of the line is treated as a comment and ignored by the compiler Convention The comment attached to the end though it is not needed indicates the name of the block or routine that is terminating It used to be the convention that basic words are in lower case and identifiers are in upper case You will find this in much of the documentation It is not required Example 2 2 This is an illustration of a main program It contains variable declarations creation of resources input process activation starting a simulation and calling a routine Don t worry about the details now they will be explained later This would not run by itself main define title as a text variable define no of tellers as an integer variable define lambda and mu as double variables SIMSCRIPT II 5 Simplified create every teller 1 read no of tellers lambda and mu let u teller 1 no of tellers activate a customer now start simulation call report calling a subroutine end main 2 3 Variables Variable names can be any combination of letters digits and periods that contains at least one letter or two or more nonterminal periods Variables should be explicitly declared with a define variable list statement which specifies a list of variables as being of a given mode Example 2 3 Here we define one
17. at is because it is For comments on this see Law and Larmey 1984 lor in another routine 32 Acknowledgements 22If you do not balance the request and relinquish pair your program may grind to a halt Because the largest integer that the seeds can take is 2 1 Ves Valerie there is a poisson distribution poisson f Mean STREAM but it is never used in simulations Understand Never ZRemember you can only tally global variables though it may sometimes be zero 33
18. cess is a sequence of events that describes the experience of an entity as it lives its lifetime For example a message turns up in a computing network it makes transitions between nodes waits for service at each one and eventually leaves the system All these are events In a process is represented as an entity associated with a process routine that describes the life cycle This entity is a temporary entity but is defined in a separate section of the preamble as a process A process can have attributes Different individual processes e g individual customers are created as the program runs The routine which describes the sequence of events is called the process routine and is written in the program as a routine with the same name as the entity 3 4 1 Defining a Process A process entity is defined with or without attributes in a processes section of the preamble Processes can own and belong to sets 17 SIMSCRIPT II 5 Simplified Example 3 11 Here we define a message process with no attributes a clock and a customer process with attributes preamble normally mode is undefined processes include message a process with no attributes every clock has a cl int define cl int as a real variable every customer has an cu Arrival time define cu Arrival time as a real variable end preamble 3 4 2 Process Routine The process routine is like other routines declared after the main block but uses the keyword process Its
19. created create a customer called Fred let cu Arrival time Fred time v activate the customer called Fred now Processes do not have to be activated immediately Example 3 15 Here we activate a Job to start at some random time in the future and activate a customer to be called Fred immediately and a bus when time v becomes 120 0 time units The word a indicates that these processes are being created activate a Job in exponential f 13 33 2 hours activate a customer called Fred now activate a Bus called b at 120 0 units 3 4 4 Activating a Process with Attributes and Arguments A process with attributes may have a corresponding routine with arguments that correspond in mode but not name to the attributes of the process entity Example 3 16 For the customer process definition shown in Example 3 11 a corresponding process routine fragment might be process customer ArrTime define ArrTime as a real variable end customer We can then activate the process and at the same time assign a value of 13 3 to the attribute cu Arrival time by either of the following methods 1 Assign an cu Arrival time with the value of the process argument ArrTime when the routine starts Example 3 17 Process argument used activate a customer called Fred given 13 3 now 2 Set the value of the attribute and then activate the process This ignores the process argument Example 3 18 3 step process create a customer called Fred let cu
20. dimensional arrays define Vector as a 1 dimensional integer array define Matrix as a 2 dimensional real array Before an array can be used its dimensions must be reserved in the main block or a subprogram not in the preamble This allows one to have arrays where the number of elements is not known until the program is running Example 2 5 Reserving dimensions for the arrays defined in Example 2 4 The first line provides a 10 element vector of integers referred to as Vector 1 to Vector 10 The second a 5 by 7 matrix of real numbers whose elements are referred to as Matrix i j for example reserve Vector as 10 reserve Matrix as 5 by 7 2 4 The Preamble The preamble is the section where global variables are defined It must precede the main program and other routines and contain no executable statements To ensures that any variables not declared are flagged by the compiler the preamble must contain the line normally mode is undefined Example 2 6 A preamble showing declarations of two processes some resources and a number of global variables The tally and accumulate statements set up statistical monitoring routines Don t worry about the details at the moment The idea is to see the sorts of declarations that occur in a preamble It has no executable statements preamble normally mode is undefined processes every customer has an Arrival time define Arrival time as a real variable resources include Teller define no of tel
21. ding process one that is waiting for an event to occur can be interrupted and later resumed by another routine Example 3 24 Here we are in some routine not the customer routine The customer called Fred is interrupted filed in a set It is held there for 20 0 units and then resumed interrupt the customer called Fred now 21 SIMSCRIPT II 5 Simplified file Fred in Interrupted Set wait 20 0 units remove the first customer called Fred from the Interrupted Set resume the customer called Fred Example 3 25 In this program example the Arrival Generator is interrupted by the terminating process Close Doors This routine prints out a report and then stops the program even though some processes have not yet finished First we look at the preamble and main blocks preamble normally mode is undefined processes include Arrival Generator and Close Doors every customer has a cu number define cu number as an integer variable define Day Length Mean sojourn as real variables define count departs and count arrivals as integer variables end preamble main call Read Data reads 3 global variables count departs 0 count arrivals 0 activate an Arrival Generator now activate a Close Doors in Day Length units start simulation it starts operating here call Report end main Example 3 26 Following on from Example 3 25 we list the processes and routines process Arrival Generator define i as an integer variable for 1 1 to 100000
22. e mean and Sd Wait as the std dev of Waiting time end preamble Later in the main part of the program the mean and standard deviation of the Waiting time can be used print 1 line with Avg Wait and Sd Wait thus Waiting time mean gd seres eet 28 Statistical Aspects of Simulation 4 2 2 Accumulate accumulate is intended to monitor variables that are continuous in time such as the length of a queue Although it changes discretely there is always a queue length existing accumulate calculates the time integrals of the value such as the average queue length Example 4 5 Here the queue at the Teller is to be monitored to determine the average of the number waiting for the Teller held in N Q Teller preamble resources include Teller accumulate Avg Line as the mean of N Q Teller end preamble Then in the main part of the program we could find out the average length of the line so far print 1 line with Avg Line thus The average number waiting so far is tally and accumulate can calculate a number of different statistics number sum mean sum of squares mean square variance std dev maximum minimum 29 SIMSCRIPT II 5 Simplified 30 5 Acknowledgments Students in OPRE352 and COMP349 classes have year by year improved these notes by their comments and questions I am also particularly grateful to Jay Braun the author of the Reference Handbook CACI83 1997 and now with JPL who
23. e multiply dimensioned and can even be ragged where the rows are not all of the same length In Unix systems such a file can be read by redirection For example when running program harbour that is written to read from the terminal and write to the terminal without changing the program we can make it read from datafile and write the results to file results using harbour lt datafile gt results See the definition of variable list in the Reference handbook See the documentation for others Sit also has a case statement Or always otherwise Or in Global variables See the Reference Handbook 124 trace is an output record that lists every event and the simulation time it occurred It is essential for debugging simulation code and can also be analyzed after a run to produce statistical results We will be using traces frequently Other time units are days hours and minutes Convention unless the simulation is actually operating in days hours and minutes the term units will be used to measure time At least one process must be activated before the simulation is started otherwise no simulation will occur See section 3 4 to find out more about processes 16 Pidd 1992 treats entities more fully The a is important You can use may belong to or can belong to instead of belongs to I get an error if the bracketed method is used though it is documented in the Reference handbook 20 f this sounds a bit complicated th
24. ed must be surrounded by a do oop pair Example 2 13 Some examples of looping program structures Here in each case 100 values are read sequentially into the vector x for i 1 to 100 do read x 1 loop leti 1 until i gt 100 do read x i add 1 toi loop leti 1 while i lt 100 do read x i add 1 toi loop 2 7 1 Selector Phrases The for while and until statements can be enriched by using one or more selector phrases to accept or reject a loop iteration The when and unless phrases test the value of a logical expression and execute the inside of the loop if appropriate Example 2 14 Here baggage is only counted if it is over 1 except if it belongs to Vignaux SIMSCRIPT II 5 Language Elements for count 1 to No of seats when Baggage count gt 1 unless Owner count Vignaux do add Baggage count to Total loop 2 8 Routines Routines in SIMSCRIPT I 5 are like subroutines or procedures in other programming languages They are declared after the main block and not inside it They are called from other subprograms not the preamble Of course they may define local variables and use global variables Example 2 15 Here a routine is defined It has a local variable i and refers to Num Ambulances which we assume is global and defined in the preamble routine Initialise define 1 as an integer variable read Num Ambulances leti 0 until i eq Num Ambulances do leti it 1 create an Ambulance activate this
25. ess needs work done at a particular sort of Machine modeled as a resource If not enough Machines are available the Task will have to wait until one becomes free The Task will then have the use of a Machine for however long it needs It is not available for other Tasks until it is released These actions are all automatically taken care of by the resource A resource can have a number of different types There may be three types of Machine resource perhaps lathe cutter and polisher A Ship may be a tanker a general cargo ship or a ferry Each different type of a resource has a number of units This records how many of that type there are initially 23 SIMSCRIPT II 5 Simplified In a resource is modeled as a special kind of permanent entity A process gets service by requesting and when it is finished by relinquishing the resource A resource maintains a set a queue or list of processes using units of each type the resource and another set of processes waiting for units of it These sets are defined and updated automatically Resources are defined in the preamble in a special section labelled resources A resource can have user defined attributes Example 3 28 Here Teller is defined as a resource without user defined attributes Ma name is a user defined attribute for the resource Machine resources include Teller every Machine has a Ma name define Ma name as a text variable A resource also has standard attributes defined automa
26. guage Elements Example 2 22 The function code would appear after the main block and would look something like this function Normal fn Mean Std Dev define Mean and Std Dev as double variables return XXX some arithmetic result end Normal fn Example 2 23 Jt would then be called like this let x Normal fn 10 0 2 1 note the decimal points for doubles Here is an example of a complete program with a preamble and a function that multiplies two variables Example 2 24 The multiply function is declared in the preamble and defined later It is called in the main block preamble normally mode is undefined define x y and z as double variables define multiply as a double function given 2 arguments end preamble main read x y let z multiply x y print 1 line with x y z thus doblek Xe times Peek ek jg deleleleletek ek end main function multiply a b Definition of the function define a b as double variables return a b end multiply 2 9 Predefined Elements There are many pre defined functions routines variables and constants You do not have to define these Pre defined elements have special suffices for example f for functions r for routines v for variables and c for constants Some examples are Function abs f arg absolute value of arg Routine date r the current date Variable hours v hours per day value of Constant pi c 11 SIMSCRIPT II 5 Simplified 12 3 Simulation with SIMSC
27. iate so we can specify that a general purpose owner the system can own a set When you define an entity in the preamble you must specify what sets it can belong to and what sets it owns Example 3 8 Here each of the Job entities has its own list of Tasks to be done the Task list held as a set The Job can be put on it belongs to the single Job queue which is owned by the System preamble temporary entities every Task has a Tk duration and belongs to a Task list define Tk duration as a double variable every Job has an Jb arrival time owns a Task list and belongs to a Job queue the system owns the Job queue end preamble Sets queues 1f not further defined are assumed to have a normal FIFO First in first out or First come first served Otherwise they can be defined as being a LIFO set Alternatively a set can be ranked by combinations of attributes of the entities that can belong to it This is specified when the belongs phrase 1s used See the define as a set in Example 3 9 Example 3 9 Here the Task list contains Tasks filed in order of low values ascending order of Tk duration temporary entities every Task has a Tk duration and belongs to a Task list define Tk duration as a double variable define Task list as a set ranked by low Tk duration Entities are put into and removed from sets by statements in the routines of the program They are added to a set using the file statement See line 5 in
28. lation with SIMSCRIPT ILS 13 3 1 Simulation TIME eyscsussnescndccciisavenssnesseseasdscoasassssipaussdosecuaiaavessencensasssaatsSevnadapseans 13 3 2 DO UU SR RTT n la ep ER eT 14 3 2 1 Creating and using Temporary Eniities 14 322 JAlt bules of Elles uis tete Del Kel de Kak eb ken 15 3 3 S ES caa cemere Del iusso k k ek EW N k SK En a kla a ek B G R DERA se d5n an a E kU KOS NEV Ide Cet AUTEUR 16 3 4 PHOGCOSSES ET 17 3 4 1 Defining a PIOGBSS cioe c e Sad eei 17 34 2 Process ROIG o amet ate OS Nee ed ee eo 18 3 4 3 Creating a Process Entity 18 3 4 4 Activating a Process with Attributes and Arguments 19 3 4 5 Elapsing Time in a Process eene 20 3 4 6 A Complete Program Using wait Commande 20 3 4 7 Interactions of Processes seen 21 SIMSCRIPT II 5 Simplified 348 Inter puolis oe o e e e Ed 21 3 5 PROS OUP CES ccn c poti HEN Te SERE R A RU h WEAR ONAN E VO QEY n DAR RERO MI NEREYE ODER V33441 495 Sosi 23 3 5 1 Using FRESOURCES ea oues aturtee eda bafi utadidictuate eut 25 3 6 Standard Attributes ssicisccdscssscseccassiessensioveresscsseasseradsseededsdoeduavsccsesdbassasetuananseeds 25 4 Statistical Aspects of Simulation 27 4 1 Random Number Generation eee eee e eerte ee eee eene eene
29. lers and no of customers SIMSCRIPT II 5 Simplified as integer variables define Time in bank and Waiting time as real variables tally Avg Wait as the average of Waiting time accumulate Avg Line as the average of N Q Teller end preamble 2 5 The Assignment Statement All statements start with a key word such as let add subtract though the et can be eliminated if preferred Example 2 7 The first two lines show assignments with the et key word The next shows an assignment without let The next is an arithmetic assignment and the last two show what are effectively assignments using add and subtract let Teller 1 let closing time closing time hours v Number of Tellers 10 key word let is omitted here let no of customers no of customers 1 add 1 to no of customers subtract 1 from no of customers 2 6 Input and Output In this introduction we will use only a simple free format read statement and one simple and one formatted print statement More complicated ones are available 2 6 1 Free form Input read The free form read variable list statement is the simplest form of input The variable list can have variables of any mode Data can be entered from the terminal i e the system input file or read from a file Be careful with variables of mode text as the value entered cannot contain blanks Example 2 8 This read statement assigns values to the 4 variables Note that in statements are not limited to a
30. nformation about it Attributes can be used to identify a sub class of entities e g red cars or values for an individual entity a customer number or to control its behavior The programmer can define attributes for the entities in the program We define an entity with attributes by the every statement in the temporary entities section of the preamble instead of the include statement You state what attributes the entity has and define their modes Convention The modes of attributes of entities are defined immediately they are specified and are given names that start with a prefix indicating the entity that they belong to Example 3 6 Here we define temporary entities without Task and with customer attributes preamble normally mode is undefined temporary entities include Task no attributes every customer has a cu Arrival time define cu Arrival time as a double variable end preamble Later in the program you can use the attribute indexed by the global entity name or a pointer variable Example 3 7 Using the Fred pointer variable to set the Arrival time for that particular customer main define Fred as a pointer variable create a customer called Fred let cu Arrival time Fred 11 4 end main 15 SIMSCRIPT II 5 Simplified 3 3 Sets A set is an ordered list of entities like a queue Sets must be defined in the preamble and must have an owner The owner is often another entity In some cases this is not appropr
31. number All the seed values are different A stream s seed value can be found from the variable seed v S The stream is updated using one of the random variable functions All these have the stream as a parameter and update that stream one or more times whenever they are called Example 4 1 Generating a random variable from stream 3 let S 3 let X random f S In this example the seed value for stream 3 is updated to the next random integer and the real value X seed v 3 2 1 is returned as a real random variable Thus 0 lt X lt 1 Thus random f S generates apparently uniform random deviates between 0 and 1 It uses one of the 10 random number seed variables Each seed sequence of random integers is supposedly independent of of the others The initial values of the seed integers the starting seeds from each of the STREAMs are initialized by at the start of a run They are listed at the start of Appendix C of Russell 1983 For example seed v 1 2116429302 You can supply your own initial integer values if you want Example 4 2 Set the initial seed value for stream 3 to 2345 let seed v 3 2345 Pseudo random variables can be generated from a number of distributions e binomial f N P STREAM e erlang f Mean K STREAM e exponential f Mean STREAM e gamma f Mean K STREAM e log normal f Mean StdDev STREAM SIMSCRIPT II 5 Simplified e normal f Mean StdDev STREAM e randi f Start Finish STR
32. omer points to this memory space When we create another customer the same global integer variable customer then points to the location of the new entity c f the new statement in many modern languages We would not use that global value but define and use a pointer variable to refer to the new entity So it is better and our convention to create temporary entities in the following form where PV is previously defined as a pointer variable PV can then be used to refer to the new entity Example 3 4 Creating a customer with a pointer that can be used to refer to it create a customer called PV An entity can later be destroyed It is best to do this by way of the pointer variable Just as the create statement needed the entity as well as the pointer so does the destroy statement 14 Simulation with SIMSCRIPT II 5 There is an important difference between the create and destroy statements We create a customer called PV but destroy the customer called PV Example 3 5 Here we define pointer variables Fred and Valerie which are used to access the two different temporary customer entities We then get rid of Fred using the destroy the command Note the different usage of a and the in the two statements define Fred Valerie as pointer variables create a customer called Fred create a customer called Valerie destroy the customer called Fred 3 2 2 Attributes of Entities An attribute is a property of an entity that conveys extra i
33. single line read no of tellers lambda title and closing time Since the list of variables can use both commas and the word and we could also write the above read statement like this read no of tellers and lambda and title and closing time 2 6 2 Quick and dirty output list SIMSCRIPT II 5 Language Elements This is used to help in debugging but should not be used in the final forms of programs in assignments The ist variable list displays the values of the variables in the variable list on the screen Example 2 9 This list statement prints the values of variable x lambda and no of tellers list x lambda and no of tellers This results in the following output X 2 0000000000 LAMBDA 5 3300000000 NO OF TELLERS 4 0000000000 2 6 3 Output with a Template print The print variable list thus statement introduced here is the main form of output we will use in the course It prints the values of every variable in the variable list in a form specified by a template The template is a pattern showing how the values are to be presented It can contain words other than the data being printed Every variable in the variable list will have a corresponding asterisk pattern Integer and text mode variables should be printed with the form the number of indicating how many digits or characters to print Real and double mode variables will have a pattern including a decimal point somewhere such as for a val
34. tically See Section 3 6 These record how many units of each type of the resource are free how many processes are waiting for it etc For example the number of types of a resource R is held in the variable N R Type i is referred to as R i where i to N R Each type has a number of units The number of units of type i is referred to as U R i Once a resource has been defined in the preamble it must have storage allocated for its attributes in the main block First you must specify the number of types N R then you create all the types create every R then you specify how many units of each type U R i Example 3 29 A group of Machines a resource might have 2 different types N Machines 2 There can be different numbers of units of each type let N Machines 2 the number of TYPES create every Machine creates storage let U Machine 1 4 the number of UNITS of type 1 let U Machine 2 1 the number of UNITS of type 2 You can get information about the set of processesthat are using units of the resource and those of processes that are waiting For resource R the set using units of type i is known as _X R i the set waiting for it as O R i Then of course since Q R i is a set we can find out how many processes are waiting from the set attribute N O R i Example 3 30 for the Machines in Example3 29 look at type 1 Machines only there are 4 of them Q Machine 1 the set of processes waiting for a type 1
35. ue with 3 digits or spaces before the decimal point and 2 after it Example 2 10 The general form is print N lines with variable list thus N lines of template with one group of or for every variable However you must be careful to count the exact number of lines used One common error is to use too few lines and try and print from the next line which may be part of the program Convention Leave an extra blank line after a print statement Example 2 11 This print statement prints 5 lines with values of the 7 variables or arithmetic expressions print 5 lines with no of tellers lambda mu and closing time hours v Avg Line Avg no of Custs and Avg Wait Minutes per day thus N Jambda mu closing time Avge line Avge customers Avge wait next program line here thus leaving a blank SIMSCRIPT II 5 Simplified after the print statement for safety 2 7 Program Flow SIMSCRIPT II 5 has all the usual program structures such as if then else or if else endif for do loop until and while loops etc The if structure has no then and the statement is terminated by endif The else part can be omitted but the endif must be retained Example 2 12 An example of the if structure ifA gt B let Maxvalue A read C else let Maxvalue B read D endif while loops are similar to until loops For all the iterative structures the group of statements to be execut
36. ulations end Profit Calc Example 2 20 We could call the routine like this call Profit Calc 50000 0 yielding the Profit A routine finishes when the program drops off the end of the routine You can finish at another part by the return statement WARNING does not automatically convert integer mode arguments to real or double So don t forget to put the decimal point in real or double arguments when you call a routine 2 8 2 Functions Functions are routines that return a value and can be called as part of an arithmetic expression The value is returned by using the return with or the return statement They are not executed using the ca statement like routines but are used within expressions to return a value They must be defined as functions in the preamble In this definition you can set the mode and you can and should state the number of given arguments Remember that the arguments and any other local variables are not recognized outside the function The only communication with the main and other routines is via the arguments in the call command and the return value Of course there are also many pre defined functions which you do not have to define yourself Example 2 21 We define a Normal fn In the preamble we define it as a double function and specify the number of arguments preamble normally mode is undefined define Normal fn as a double function given 2 arguments end preamble 10 SIMSCRIPT II 5 Lan
37. variable of integer mode two of double mode and one of text mode define Next Customer as an integer variable define Weight Length and Height as double variables define my title as a text variable The variable list can take a number of alternative forms The variable names can be separated by any of the following or and or and The choice is up to you and is intended to make the program more readable See CACI83 1997 Similarly the word an which could be a in the first definition above is optional and is there for readability Convention All variable names must be defined explicitly 2 3 1 Modes Variables can be of a number of modes called types in other languages e integer e real e double increased precision reals e text for strings of text e pointer integer real and double modes are intended for numerical calculations text for string handling and pointer for handling temporary entities and processes to be considered in Section 3 2 1 At the start of a program all variables are initialized to zero or a blank value SIMSCRIPT II 5 Language Elements 2 3 2 Local and Global Variables A variable is only known within the routine it is defined in It is a ocal variable Variables declared in the preamble Section 2 4 are global and are know and can be used throughout the program 2 3 3 Arrays SIMSCRIPT II 5 does have arrays They are defined as follows Example 2 4 Defining 1 and 2
38. xoe cere sene eee ce ceke ae 27 4 2 Statistical MOnlfOFIDo eios ehe es robe te ouoe etas t Eun o ehe aUa boe Un ce eR eP es s pee ee ied 28 DNUS MET m nore ec SPR e A XA N A ote 28 4 2 2 Accumulate ene a eR n cnt quodsi Rs 29 5 Acknowledgments eerte 31 5 1 R fe P l CS sy diode pedes poii a grido e kana V H R es Gu SEVEKE seda WISE FU dde K S SHE WEHA KO Guna ESA G 31 MIDI TEOGUIOIGS cs redit not tula dein stetit be qan oe EUOLA 31 Abstract SIMSCRIPT IL5 is a powerful simulation language in active use for major simulations particularly in engineering applications These notes illustrate just enough of the features so that simple simulations programs can be written SIMSCRIPT II 5 Simplified 1 Introduction SIMSCRIPT IL5 is a powerful free form English like general purpose simulation programming language It supports the application of software engineering principles such as structured programming and modularity which impart orderliness and manageability to simulation models Russell 1983 is available for a range of computers including PCs running Windows and NT and also Unix workstations These notes introduce only a few features of enough for simple simulations Many features of the language are left out You are strongly urged to refer to the more comprehensive information found in the manuals such as CACI83 1997 and CACI89 1989 and other books such as CACI97 1997 and
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