SCICOS - A Dynamic System Builder and Simulator User's Guide ∗
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1. DASKR used in Scicos DIFF_f and CONSTRAINT_f are general Implicit Blocks However implicit blocks are included in Scicos to allow the integration of Modelica blocks 4 Time dependence and inheritance To avoid explicitly drawing all the activation signals in a Scicos diagram a feature called inheritance is provided in Scicos In particular if a block has no activation input port it inherits its activation signal from its regular input signals And for blocks which are active permanently they can be declared as such time dependent and they do not need input activation ports Note that time dependent blocks do not inherit xd Ax Bu y Cx Du r Figure 3 An example using a block with zero crossing surface 5 Block construction A new block can be constructed as a Super Block by interconnection of basic blocks and compiled As for a new basic block it can be defined by a pair of functions e an Graphical Interfacing function for handling the user interface e a Computational function for specifying its dynamic behavior The Graphical Interfacing function is always written as a Scilab function See Scilab functions in lt SCIDIR gt macros scicosxh for examples The Computational function can be written in C or Fortran See lt SCIDIR gt routines scicos for examples But it can also be written in Scilab language C and Fortran routines dynamically linked or permanently interfaced with Scilab give the better resu2. includes preprogrammed event firing times lt 0 if no firing e dep_ut udep timedep 10 5 2 udep boolean True if system has direct feed through i e at least one of the outputs depends explicitly on one of the inputs timedep boolean True if block is time dependent label character string used as block identifier This field may be set by the label button in Object menu Computational function The Computational function evaluates outputs new states continuous state derivative and the output events timing vector depending on the type of the block and the way it is called by the simulator 5 2 1 Behavior Simulator calls the Computational function for performing different tasks Initialization The simulator calls the Computational function once at the start for state and output initialization inputs are not available then Other tasks such as file opening graphical window initialization etc can also be performed at this point Re initialization The simulator can call the block a number of times for re initialization This is another oppor tunity to initialize states and outputs e g in cold start case But at this time the inputs are available Outputs update The simulator calls for the value of the outputs Thus the Computational function should evaluate 4 States update One or more events have arrived and the simulator calls the Computational function to update the states x and z according
3. insz inptr nout outsz outptr nevout evout nrpar rpar nipar ipar ng g ztyp jroot label work nmode mode The following Scilab functions can be used to obtain additional information and perform other operations e curblock returns the current block number in the structure cpr e scicos_time gives the current time e phase_simulation returns the simulation phase e set_blockerror i set the error flag if the computational function encounters an error Examples Consider the following computational function which is the code for the summation block in Scicos it is of type 4 include scicos_block h include lt math h gt void summation scicos_block block int flag int j k if flag 1 if block gt nin 1 block gt outptr 0 0 0 0 for 3 0 3j lt block gt insz 0 3 block gt outptr 0 0 block gt outptr 0 0 block gt inptr 01 j else 13 for 3 0 3j lt block gt insz 0 3 block gt outptr 0 3 0 0 for k 0 k lt block gt nin k if block gt ipar k gt 0 block gt outptr 0 j block gt outptr 0 j block gt inptr k j jelsel block gt outptr 0 3 block gt outptr 0 3 1 block gt inptrI Ik j The following is a simple example of the compuational function of a type 5 block This block realizes the sine function function block sin5 block flag 1f flag 1 then for j 1 block insz 1 block outptr 1 j sin block inptr 1 3 end end endfunction Comp
4. the block is defined by y t A t x t z t u t p Ne 4 and is constant when the block is not active Finally RBB s can generate activation signals of event type If it is activated by an event at time te the time of each output event is given by tevo k te 2 te u te p Ne 6 where tevo is a vector of time each entry of which corresponds to one activation output port The absence of event corresponds to a time smaller than the current time Event generations can also be pre scheduled Pre scheduling of events can be done by setting the initial firing variables of blocks with event output ports There are situations where a block is activated not from an outside activation source but because of an internal zero crossing A zero crossing occurs when a zero crossing surface traverses zero A block can have any number of zero crossing functions surfaces s t k t x t z t u t 6 When a zero crossing occurs the block is internally activated which is similar to an external activation with ne 1 Zero crossing is used for example to generate zero crossing events A few examples of blocks generating output activations following a zero crossing can be found in the Threshold palette Zero crossing in conjunction with the mode flag not discussed here is also used to model non smooth dynamics of certain blocks Consider for example the absolute value block y u if u gt 0 and y u otherwise This function
5. to 2 and 3 State derivative computation The simulator is in a continuous phase the solver requires This means that the Computational function must evaluate 1 Output events timing The simulator calls the Computational function about the timing of its output events The Computational function should evaluate 5 Ending The simulator calls the Computational function once at the end useful for closing files free allocated memory etc The simulator uses a flag to specify which task should be performed see Table 1 State derivative computation Outputs update States update Output events timing Initialization Ending Re initialization for explicit blocks Re initialization for implicit blocks zero crossing functions and mode 0 1 2 3 4 5 6 7 9 Table 1 Tasks of Computational function and their corresponding flags 11 5 2 2 Types of Computational functions In Scicos for to guarantee backward compatibility Computational functions can be of different types and co exist in the same diagram Old types are listed in Table 2 It is highly recommended to use new types 4 and 10004 for C code and 5 and 10005 for Scilab code from now on Funcion ype Sob Fontan CT Commens 7 Fixed calling sequence for explicit blocks Varying calling sequence for explicit blocks Fixed calling sequence for explicit blocks Inputs outputs are Scilab lists for explicit blocks Varying calling sequence for implicit bl
6. used x is the new data structure of the block y is not used typis not used e job define initialization of block s data structure name of corresponding Computational function type number and sizes of inputs and outputs etc argl arg2are not used x is the data structure of the block y 1s not used typ is not used 5 1 2 Block data structure definition Each Scicos block is defined by a Scilab data structure as follows mlist Block graphics model gui doc graphics model gui doc where gui is a string containing the name of the corresponding Graphical Interfacing function and graphics is the structure containing the graphical data graphics mlist graphics orig sz flip exprs pin pout pein peout gr_i id orig sz flip exprs pin pout pein peout gr_i id e orig 2 x 1 vector the coordinate of down left point of the block shape e sz vector w h where w is the width and h the height of the block shape e flip boolean the block orientation If true the input ports are on the left of the box and output ports are on the right if false the input ports are on the right of the box and output ports are on the left e exprs column vector of strings contains expressions answered by the user at block set time e pin column vector of integers If pin k 0 then kth input port is connected to
7. 3 1 Explicit Blocks There are two types of Basic Explicit Blocks in Scicos Regular Basic Blocks and Synchro Basic Blocks 3 1 1 Regular Basic Block Regular Basic Blocks RBB can have two types of inputs and two types of outputs ports regular inputs activation inputs regular outputs and activation outputs ports Regular inputs and outputs are interconnected by regular links and activation inputs and outputs by activation links Note that activation input ports are placed on top and activation output ports at the bottom of the blocks Such a block can have a continuous state x and a discrete state z If it does have an x and if u denotes its regular input then when the block is active over an interval of time x evolves continuously according to t f t Z U p Ne 1 where f is a vector function p is a vector of constant parameters and ne is the activation code which is an integer designating the port s through which the block is activated In particular if activating input ports are 71 72 n then n Ne gt D OK j 1 On the other hand activated by an event the states x and z jump instantaneously according to the following equations te P ne 2 te p ne 3 Nx A Oe NM ER NA e where te denotes the event time The discrete state z remains constant between any two successive events so z tz can be interpreted as the previous value of z During activation times the regular output of
8. SCICOS A Dynamic System Builder and Simulator User s Guide R Nikoukhah and S Steer INRIA Contents 1 Introduction 1 2 Scicos editor 2 2 1 Parameter adaptation cg Pi ee Bae A ew Bete Ob AAA A ee 3 202 SSIUMUIAION ee sak ca Bocce eet a E ogee Rise tay ae ea eR ead chee a enna Bik wee Rae ee tao 3 2 3 Otherfunctionalities miei a we do we Ge oe ee eo 3 3 Basic Blocks 3 3a EXpheitiBIOCks aces ee eee gy oe ne a ee ee ee ee ee ie eee 3 3 1 1 Regular Basic Block 302 24 eee wee bee Pee ew ee a eee Ba eas 4 3 1 2 Synchro Basie Blocks 2 4 50 fb Awe ha oe BE aR a ee ae eee Bay 5 3 2 Implicit blocks pds e poe bf a SE RGAE ES peata bo BA paa 5 4 Time dependence and inheritance 5 5 Block construction 6 5 1 Graphical Interfacing function aoaaa 6 DIO ASYD AR tr a Gel hte O ar bee e ee E de Mena 6 5 1 2 Block data structure definition ee 9 5 2 Computational function 2 a 11 ZO BERAVIOL pudis eae e cdots A enh ie be be id dde 11 5 2 2 Types of Computational functions a 12 6 Conclusion 14 1 Introduction Scicos Scilab Connected Object Simulator is a Scilab package for modeling and simulation of explicit and implicit dynamical systems including both continuous and discrete sub systems Scicos includes a graphical editor for con structing models by interconnecting blocks representing predefined basic functions or user defined functions Associated with each signal in Scicos is a set of tim
9. als gen erated by the block For example the Clock block generates an activation signal composed of a train of regularly spaced events in time If this output is connected to the input activation port of a scope block such as the MScope block it specifies at what times the value of the inputs of the scope must be displayed 2 Scicos editor In Scicos systems are modeled by interconnecting blocks and subsystems Super blocks blocks can be found in various palettes or be defined by user Scicos has an easy to use graphical user interface for editing diagrams To start the editor in Scilab type scicos This opens up Scicos main window Construction of Scicos model typically consists of e opening one or more palettes using Palettes button in the Edit menu e copying blocks from palettes into Scicos main window this can be done by selecting the copy button in the Edit menu then clicking on the block to be copied and finally in the Scicos main window where the block 1s to be placed e connecting the input and output ports of the blocks by selecting first the 1ink button in the Edit menu then clicking on the output port and then on the input port or intermediary points before that Note that to make a link originate from another link to split a link user should first click on an existing link where split is to be placed and then on an input port or intermediary points before that The process of link creati
10. ation output ports double evout delay times of output activations int nrpar number of real parameters double rpar real parameters of size nrpar int nipar number of integer parameters int ipar integer parameters of size nipar int ng number of zero crossing surfaces double g zero crossing surfaces 12 int ztyp boolean true only if block MAY have zero crossings int jroot vector of size ng indicating the presence and direction of crossings char label block label void work pointer to workspace if allocation done by block int nmode number of modes int mode mode vector of size nmode scicos_block The following C functions can be used within a compuational function of type 4 to obtain additional information and perform other operations e double get_scicos_time returns the current time t e void set_block_error int used by the block to signal an error to the simulator e int get_phase_simulation returns the simulation phase 1 or 2 e int get_block_number returns the block number Computational function type 5 This type is for computational function expressed in Scilab The calling sequence is block func_name block flag where block is a Scilab structure similar to the C structure used in the C computational function of type 4 The fields of block are scicos_block nevprt funpt type scsptr nz z nx x xd res nin
11. e indices called activation times on which the signal can evolve Outside their activation times Scicos signals remain constant see Figure 1 The activation time set is a union of time intervals and isolated points called events Scicos is a Scilab toolbox This version of Scicos is included in Scilab 3 1 1 For more information see http www scicos org signal remains constant outside of activation __ time i y oe A AA I if a AS SSi discrete activation continuous times events activation time Figure 1 A signal in Scicos and its activation time set Signals in Scicos are generated by blocks driven by activation signals An activation signal causes the block to evaluate its output as a function of its input and internal state It also causes the block to update its states if any The output signal which inherits its activation time set from the generating block can be used to drive other blocks Blocks are activated by activation signals which are received on activation input ports placed on top of them A block with no input activation port is either permanently active called time dependent or it inherits its activation times from the union of activations times of its input signals If the block is neither permanently active nor has any inputs then it is never active during simulation it is a constant block Ports placed at the bottom of blocks are output activation ports The outgoing signals are activation sign
12. he vector of y coordinates of input ports typ is the vector of input ports types 1 for regular and 2 for activation In general we can use the standard_input function e job getoutputs returns position and type of output ports regular and activation arg is the data structure of the block arg2 is not used Implicit_Explicit sinusoid generator gt 00 p WWW i Q Hai gt gt Imp Ex If in gt 0 S H then else p l random generator P Scope Figure 5 An example using implicit and explicit blocks The Modelica extension not discussed here provides a more natural setting for this type of modeling x is the vector of x coordinates of output ports y is the vector of y coordinates of output ports typ is the vector of output ports types In general we can use the standard_output function e job getorigin returns coordinates of the lower left point of the rectangle containing the block s silhouette arg is the data structure of the block arg2 is not used x is the x coordinate of the lower left point of the block y is the y coordinate of the lower left point of the block typ is not used In general we can use the standard_origin function e job set opens up a dialogue for block parameter acquisition if any arg is the data structure of the block arg2 is not
13. is not differentiable at 0 In this case a mode is defined to specify at the start of the integration period whether u is positive To make sure the integration stops when the sign of u changes a zero crossing surface is introduced at zero During the integration period which could end because of the zero crossing the output y is computed as follows y wif m 1 and y u otherwise After the zero crossing the mode is recomputed and the integration continues Figure 2 An example using Regular Basic Block 3 1 2 Synchro Basic Block Beginning from Scilab 2 7 version custom made Synchro blocks have been eliminated There are now only two Synchro blocks IF THEN ELSE and ESELECT in the Branching palette see Fig 4 Synchro Basic Blocks SBB generate output activation signals that are synchronized with their input activation signals These blocks have a unique activation input port they route their input activation signals to one of their activation outputs The choice of this output depends on the value of the regular input These two important blocks play the role of conditional statements in programming languages such as C 3 2 Implicit blocks Differential algebraic equations DAE have the form M t y f t y u where M is a singular matrix or more simpler y is a regular output and u the regular input DAB s of index_1 can be solved by the implicit solver
14. lts as far as simulation performance is concerned The Scifunc GENERIC C_block and Fortran_block blocks provide generic Graphical Interfacing func tions very useful for rapid prototyping and testing user developed Computational functions 5 1 Graphical Interfacing function The Graphical Interfacing function determines the geometry color number of ports and their sizes icon etc in addition to the initial states parameters This function also handles the block s user dialog What the interfacing function should do and should return depends on an input flag job The syntax is as follows 5 1 1 Syntax x y typ block job argl arg2 Synchro gt Abs gt gt gt event select pe sinusoid If in gt 0 E gt generator Heels if L gt COS S H MScope Figure 4 An example using the two Synchro Basic Blocks Parameters e job plot the function draws the block arg is the data structure of the block arg2 is not used X Y typ are not used In general we can use standard_draw function which draws a rectangular block and the input and output ports It also handles the size icon and color aspects of the block e job getinputs the function returns position and type of input ports regular or activation arg is the data structure of the block arg2 is not used x is the vector of x coordinates of input ports y is t
15. ocks Fixed calling sequence for implicit blocks Inputs outputs are Scilab lists for implicit blocks Table 2 Different types of the Computational functions Type 0 is obsolete Computational function type 4 All explicit new C blocks should be of type 4 Type 4 blocks should be defined as follows include scicos_block h include lt math h gt void my_block scicos_block block int flag The flag is any integer from 0 to 9 indicating the task to be preformed and block is the block structure defi ned as follows typedef struct int nevprt binary coding of activation inputs 1 if internally activated voidg funpt pointer pointer to the computational function int type type of interfacing function current type is 4 int scsptr not used for C interfacing functions int nz size of the discrete time state double z vector of size nz discrete time state int nx size of the continuous time state double x vector of size nx continuous time state double xd vector of size nx derivative of continuous time state double res only used for internally implicit blocks vector of size nx int nin number of inputs int insz input sizes double inptr table of pointers to inputs int nout number of outputs int outsz output sizes double outptr table of pointers to outputs int nevout number of activ
16. on can be stopped and current link deleted by clicking on the right mouse button Note also that at least one scope or a write to file block should be placed in any Scicos diagram to visualize or save the result of the simulation See Scicos demos for examples In addition to pull down menus Scicos functionalities can also be used through keyboard shortcuts user definable and pop up menu click on the right button 2 1 Parameter adaptation Block parameters can be modified by opening the block dialogs This can be done using the Open set button Most blocks have dialog menus which can be used to set or modify block parameters These parameters can be defined using valid Scilab expressions Scilab variables can be used in the definition of these expressions if they are already defined in the context of the diagram These expressions are memorized symbolically and then evaluated The context of the diagram can be edited by selecting the Context button It can contain any valid Scilab instruction including exec instructions to run Scilab scripts defined on file Note that in this latter case if the files are edited the user should explicitely use the Eval button to update the block parameters 2 2 Simulation A completed diagram can be simulated using Run in the Simulate menu Selecting this button results in a compila tion of the diagram if not already compiled and simulation The simulation can be stopped by clicking on the stop b
17. t later e in vector of size equal to the number of block s regular input ports Each entry specifies the size of the corresponding input port A negative integer stands for to be determined by the compiler Specifying the same negative integer on more than one input or output port tells the compiler that these ports have equal sizes e out vector of size equal to the number of block s regular output ports Each entry specifies the size of the corresponding output port Specifying the same negative integer on more than one input or output port tells the compiler that these ports have equal sizes e evtin vector of size equal to the number of activation input ports All entries must be equal to 1 Scicos does not support vectorized activation links e evtout vector of size equal to the number of activation output ports All entries must be equal to 1 Scicos does not support vectorized activation links e state column vector of initial continuous state e dstate column vector of initial discrete state e rpar column vector of real parameters passed on to the corresponding Computational function e ipar column vector of integer parameters passed on to the corresponding Computational function e blocktype string Basic block type z if ZBB 1 if SBB and anything else for except s for RBB e firing column vector of initial firing times of size equal to the number of activation output ports of the block It
18. the pin k 0 block else the port is unconnected If no input port exist pin e pout column vector of integers If pout k 0 then kth output port is connected to the pout k 0 block else the port is unconnected If no output port exist pout e pein column vector of ones If pein k 0 then kth event input port is connected to the pein k 0 block else the port is unconnected If no event input port exist pein e peout column vector of integers If peout k 0 then kth event output port is connected to the peout k 0 block else the port is unconnected If no event output port exist peout e gri column vector of strings contains Scilab instructions used to customize the block graphical aspect This field may be set with Icon sub_menu e id string unused The data structure containing simulation information is model model mlist model sim in out evtin evtout state dstate rpar ipar blocktype firing dep_ut label sim in out evtin evtout state dstate rpar ipar blocktype firing dep_ut label e sim list containing two elements First element is a string containing the name of the Computational function fortran C or Scilab function Second element is an integer specifying the type of the Computational function The type of a Computational function specifies essentially its calling sequence more on tha
19. utational functions type 10004 and 10005 These types are used to construct implicit blocks They are not discussed here Type 10004 is used mostly by the Modelica extension 6 Conclusion This document gives only a brief description of Scicos and its usage More information can be found in the manual pages of Scicos functions Scilab help under Scicos library Scicos demos provided with Scilab constitute also an interesting source of information Often it is advantageous to start off from and edit a Scicos demo rather than starting with an empty diagram More information is available on www scicos org 14
20. utton on top of the Scicos main window A compiled Scicos diagram saved as a cos file does not need compilation the next time it is loaded the saved file contains the result of the compilation It is also possible to extract just the data needed to do simulation and do the simulation without having to enter the Scicos environment This can be done using the scicosim function 2 3 Other functionalities The editor provides many other functionalities such as e saving and loading diagrams in various formats zooming and changing the point of view changing block aspects and colors changing diagram s background and forground colors placing text in the diagram printing and exporting Scicos diagrams and many other standard GUI functions The He 1 p button can be used to obtain help on various aspects of Scicos Selecting He 1p and then clicking on a block displays the manual page of the block Selecting He1p and then selecting another button displays the manual page of the button Finally an important feature in Scicos is the possibility of creating sub systems Super Blocks Clearly it would not be desirable to fit a complex system with hundreds of components in one Scicos diagram For that Scicos provides the possibility of grouping blocks together and defining sub diagrams called Super Blocks These blocks behave like any other block but can contain an unlimited number of blocks and even other Super Blocks 3 Basic Blocks
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