Configure Symbolic Dimensions for S-Function Blocks

To configure symbolic dimensions for S-function blocks, you can use the following C/C++ functions. You can configure S-functions to support forward propagation, backward propagation, or forward and backward propagation of symbolic dimensions during simulation.

Many of these functions return the variable SymbDimsId. A SymbDimsId is a unique integer value. This value corresponds to each symbolic dimension specification that you create or is the result of a mathematical operation that you perform with symbolic dimensions.

C/C++ S-Functions	Purpose
ssSetSymbolicDimsSupport	Specify whether or not an S-function supports symbolic dimensions.
mdlSetInputPortSymbolicDimensions	Specify the symbolic dimensions of an input port and how those dimensions propagate forward.
mdlSetOutputPortSymbolicDimensions	Specify the symbolic dimensions of an output port and how those dimensions propagate backward.
ssRegisterSymbolicDimsExpr	Create a SymbDimsId from an expression string (aExpr). The expression string must form a valid syntax in C.
ssRegisterSymbolicDims	Create a SymbDimsId from a vector of SymbDimsIds.
ssRegisterSymbolicDimsString	Create a SymbDimsId from an identifier string (aString).
ssRegisterSymbolicDimsIntValue	Create a SymbDimsId from an integer value (aIntValue)
ssRegisterSymbolicDimsPlus	Create a SymbDimsId by adding two symbolic dimensions.
ssRegisterSymbolicDimsMinus	Create a SymbDimsId by subtracting two symbolic dimensions.
ssRegisterSymbolicDimsMultiply	Create a SymbDimsId by multiplying two symbolic dimensions.
ssRegisterSymbolicDimsDivide	Create a SymbDimsId by dividing two symbolic dimensions.
ssGetNumSymbolicDims	Get the number of dimensions for a SymbDimsId.
ssGetSymbolicDim	Get a SymbDimsId from a vector of SymbDimsIds.
ssSetInputPortSymbolicDimsId	Set the precompiled SymbDimsId of an input port. You can call this function from inside the mdlInitializeSizes function.
ssGetCompInputPortSymbolicDimsId	Get the compiled SymbDimsId of an input port.
ssSetCompInputPortSymbolicDimsId	Set the compiled SymbDimsId of an input port.
ssSetOutputPortSymbolicDimsId	Set the precompiled SymbDimsId of an output port. You can call this function from inside the mdlInitializeSizes function.
ssGetCompOutputPortSymbolicDimsId	Get the compiled SymbDimsId of an output port.
ssSetCompOutputPortSymbolicDimsId	Set the compiled SymbDimsId of an output port.
ssSetCompDWorkSymbolicDimsId	Set the compiled SymbDimsId of an index of a block’s data type work (DWork) vector.

Generate Code from an S-Function Block with Dimension Variants

The model ex_msymbdims_sfcn_one contains an S-function that subtracts the symbolic dimension B from a symbolic input dimension, A + B. The model supports forward propagation because the symbolic dimensions of the output ports are set. The model does not support backward propagation of symbolic dimensions because the compiled symbolic dimensions of the input ports are not set.

model='ex_msymbdims_sfcn_one';
open_system(model);

The sfun_symbdims_sfcn_one.c file contains this code.

type sfun_symbdims_sfcn_one.c

/* Copyright 2014 The MathWorks, Inc. */
#define S_FUNCTION_NAME  sfun_symbdims_sfcn_one
#define S_FUNCTION_LEVEL 2

#include "simstruc.h"

#include <assert.h>

/* Function: mdlInitializeSizes ===============================================
 * Abstract:
 *   Setup sizes of the various vectors.
 */
static void mdlInitializeSizes(SimStruct *S)
{
    ssSetNumSFcnParams(S, 0); /* Number of expected parameters */
    
    ssSetNumContStates(S, 0);
    ssSetNumDiscStates(S, 0);

    if (!ssSetNumInputPorts(S, 1)) return;
    ssSetInputPortDirectFeedThrough(S, 0, 1);
    ssSetInputPortDimensionInfo(S, 0, DYNAMIC_DIMENSION);
    ssSetInputPortRequiredContiguous(S, 0, 1);
    
    if (!ssSetNumOutputPorts(S,1)) return;
    ssSetOutputPortDimensionInfo(S, 0, DYNAMIC_DIMENSION);   
    ssSetNumSampleTimes(S, 1);

    ssSetNumRWork(S, 0);
    ssSetNumIWork(S, 0);
    ssSetNumPWork(S, 0);

    ssSetNumModes(S, 0);
    ssSetNumNonsampledZCs( S, 0);
    
    ssAllowSignalsWithMoreThan2D(S);
    
    ssSetOptions(S, SS_OPTION_EXCEPTION_FREE_CODE);
    
    ssSetSymbolicDimsSupport(S, true);
}


/*If underspecified for propagation, say i/o are scalars.*/
#if defined(MATLAB_MEX_FILE)
#define MDL_SET_DEFAULT_PORT_DIMENSION_INFO
static void mdlSetDefaultPortDimensionInfo(SimStruct *S)
{
    if( (ssGetOutputPortWidth(S, 0) == DYNAMICALLY_SIZED) 
        && (ssGetInputPortWidth(S, 0) == DYNAMICALLY_SIZED) ) {
        ssSetOutputPortMatrixDimensions(S, 0, 1, 1 );
    }
}
#endif

#if defined(MATLAB_MEX_FILE)
#define MDL_SET_INPUT_PORT_SYMBOLIC_DIMENSIONS
static void mdlSetInputPortSymbolicDimensions(SimStruct* S, 
   int_T portIndex, SymbDimsId symbDimsId)
{
    assert(0 == portIndex);
    // Set the compiled input symbolic dimension.
    ssSetCompInputPortSymbolicDimsId(S,  portIndex, symbDimsId);
    const SymbDimsId symbolId = ssRegisterSymbolicDimsString(S, "B");
    const SymbDimsId outputDimsId = 
       ssRegisterSymbolicDimsMinus(S, symbDimsId, symbolId);
    ssSetCompOutputPortSymbolicDimsId(S, portIndex, outputDimsId);
}
#endif

#if defined(MATLAB_MEX_FILE)
#define MDL_SET_OUTPUT_PORT_SYMBOLIC_DIMENSIONS
static void mdlSetOutputPortSymbolicDimensions(SimStruct *S, 
   int_T portIndex, SymbDimsId symbDimsId)
{
    assert(0 == portIndex);
   // The input dimensions are not set, so this S-function only
	// supports forward propagation.
    ssSetCompOutputPortSymbolicDimsId(S, portIndex, symbDimsId);
}
#endif

/* Function: mdlInitializeSampleTimes =========================================
 * Abstract:
 *    Specify that we inherit our sample time from the driving block.
 *    However, we don't execute in minor steps.
 */
static void mdlInitializeSampleTimes(SimStruct *S)
{
    ssSetSampleTime(S, 0, INHERITED_SAMPLE_TIME);
    ssSetOffsetTime(S, 0, 0.0);
    ssSetModelReferenceSampleTimeDefaultInheritance(S);    
}
/* Function: mdlOutputs =======================================================
 * Abstract:
 *    y=u';
 */
static void mdlOutputs(SimStruct *S, int_T tid)
{
}

/* Function: mdlTerminate =====================================================
 * Abstract:
 *    No termination needed, but we are required to have this routine.
 */
static void mdlTerminate(SimStruct *S)
{
    UNUSED_ARG(S); /* unused input argument */
}



#ifdef  MATLAB_MEX_FILE    /* Is this file being compiled as a MEX-file? */
#include "simulink.c"      /* MEX-file interface mechanism */
#else
#include "cg_sfun.h"       /* Code generation registration function */
#endif

The Simulink.Parameter objects A and B contain these definitions.

type definitions.txt

A = Simulink.Parameter;
A.DataType = 'int32';
A.Value = 6;
A.Min=5;
A.Max=7;
A.CoderInfo.StorageClass = 'Custom';
A.CoderInfo.CustomStorageClass = 'ImportedDefine';
A.CoderInfo.CustomAttributes.HeaderFile = 'ImportedDefinitions.h';

B = Simulink.Parameter;
B.DataType = 'int32';
B.Value = 10;
B.Min=9;
B.Max=11;
B.CoderInfo.StorageClass = 'Custom';
B.CoderInfo.CustomStorageClass = 'ImportedDefine';
B.CoderInfo.CustomAttributes.HeaderFile = 'ImportedDefinitions.h';

The ImportedDefinitions header file contains this code.

type ImportedDefinitions.h

/* Copyright 2014 The MathWorks, Inc. */
#ifndef _IMPORTEDDEFINITIONS_H_
#define _IMPORTEDDEFINITIONS_H_
#define A 6
#define B 10
#endif

In the Configuration Paramters dialog box, the Custom Code pane contains the #include "ImportedDefinitions.h" statement.

The sfun_symbdims_sfcn_one S-function is inlined, so a TLC file with this code must be present on the path with the model and other supporting files.

type sfun_symbdims_sfcn_one.tlc

%implements "sfun_symbdims_sfcn_one" "C"


%function BlockInstanceSetup(block, system) void
%endfunction

%% Function: BlockOutputSignal =================================================
%function BlockOutputSignal(block,system,portIdx,ucv,lcv,idx,retType) void
%endfunction

%% Function: Outputs ===========================================================
%%
%function Outputs(block, system) Output


  %assign rollVars = ["U", "Y"]
  %roll idx = RollRegions, lcv = RollThreshold, block, "Roller", rollVars
    %%
    %assign u  = LibBlockInputSignal( 0, "", lcv, idx)
    %assign y  = LibBlockOutputSignal(0, "", lcv, idx)
                                                           
    %<y> = %<u>;
                                                      
  %endroll

%endfunction %% Outputs

To generate a MEX function, at the command-line, enter this command:

mex sfun_symbdims_sfcn_one.c

Building with 'gcc'.
MEX completed successfully.

Generate code for the model.

currentDir=pwd;
slbuild(model);

### Starting build procedure for: ex_msymbdims_sfcn_one
### Successful completion of build procedure for: ex_msymbdims_sfcn_one

Build Summary

Top model targets built:

Model                  Action                        Rebuild Reason                                    
=======================================================================================================
ex_msymbdims_sfcn_one  Code generated and compiled.  Code generation information file does not exist.  

1 of 1 models built (0 models already up to date)
Build duration: 0h 0m 8.7845s

View the generated code for the model. The ex_msymbdims_sfcn_one_step function contains this code. The S-function code is set inline and the symbolic dimensions A and B are in the generated code.

cfile=fullfile(currentDir, 'ex_msymbdims_sfcn_one_ert_rtw','ex_msymbdims_sfcn_one.c');
rtwdemodbtype(cfile,'/* Model step', '/* Model initialize', 1, 0);

/* Model step function */
void ex_msymbdims_sfcn_one_step(void)
{
  int32_T i;

  /* Gain: '<Root>/Gain' incorporates:
   *  Concatenate: '<Root>/Matrix Concatenate'
   *  Inport: '<Root>/In1'
   */
  for (i = 0; i < A; i++) {
    ex_msymbdims_sfcn_one_B.MatrixConcatenate[i] = 2.0 *
      ex_msymbdims_sfcn_one_U.In1[i];
  }

  /* End of Gain: '<Root>/Gain' */

  /* Gain: '<Root>/Gain2' incorporates:
   *  Concatenate: '<Root>/Matrix Concatenate'
   *  Inport: '<Root>/In2'
   */
  for (i = 0; i < B; i++) {
    ex_msymbdims_sfcn_one_B.MatrixConcatenate[A + i] = 2.0 *
      ex_msymbdims_sfcn_one_U.In2[i];
  }

  /* End of Gain: '<Root>/Gain2' */

  /* S-Function (sfun_symbdims_sfcn_one): '<Root>/Minus' incorporates:
   *  Outport: '<Root>/Out1'
   */
  {
    int_T i1;
    const real_T *u0 = &ex_msymbdims_sfcn_one_B.MatrixConcatenate[0];
    real_T *y0 = &ex_msymbdims_sfcn_one_Y.Out1[0];
    for (i1=0; i1 < ((A + B)); i1++) {
      y0[i1] = u0[i1];
    }
  }
}

Close the model

bdclose(model);

S-Function That Supports Forward and Backward Propagation of Symbolic Dimensions

This S-function transposes two symbolic dimensions. It supports forward and backward propagation of symbolic dimensions because the compiled symbolic dimension of both the input and output ports are set.

static void mdlInitializeSizes(SimStruct *S)
{
     // Enable symbolic dimensions for the s-function.
     ssSetSymbolicDimsSupport(S, true);
}

#if defined(MATLAB_MEX_FILE)
#define MDL_SET_INPUT_PORT_SYMBOLIC_DIMENSIONS
static void mdlSetInputPortSymbolicDimensions(SimStruct* S, 
   int_T portIndex, SymbDimsId symbDimsId)
{
    assert(0 == portIndex);
    
    ssSetCompInputPortSymbolicDimsId(S,  portIndex, symbDimsId);
    
    assert(2U == ssGetNumSymbolicDims(S, symbDimsId));
    
    if (SL_INHERIT == 
        ssGetCompOutputPortSymbolicDimsId(S, portIndex)) {

        const SymbDimsId idVec[] = {
            ssGetSymbolicDim(S, symbDimsId, 1),
            ssGetSymbolicDim(S, symbDimsId, 0)};
        // Register the transposed dimensions.
       // Set the output symbolic dimension to the resulting id.
  const SymbDimsId outputDimsId = 
            ssRegisterSymbolicDims(S, idVec, 2U);

        ssSetCompOutputPortSymbolicDimsId(S, portIndex, 
           outputDimsId);
    }
}
#endif

#if defined(MATLAB_MEX_FILE)
#define MDL_SET_OUTPUT_PORT_SYMBOLIC_DIMENSIONS
static void mdlSetOutputPortSymbolicDimensions(SimStruct *S, 
    int_T portIndex, SymbDimsId symbDimsId)
{
    assert(0 == portIndex);
    ssSetCompOutputPortSymbolicDimsId(S, portIndex, symbDimsId);

    assert(2U == ssGetNumSymbolicDims(S, symbDimsId));
    
    if (SL_INHERIT == 
        ssGetCompInputPortSymbolicDimsId(S, portIndex)) {

        const SymbDimsId idVec[] = {
            ssGetSymbolicDim(S, symbDimsId, 1),
            ssGetSymbolicDim(S, symbDimsId, 0)};
        const SymbDimsId inputDimsId = 
            ssRegisterSymbolicDims(S, idVec, 2U);
        // Register the transposed dimensions.
       // Set the input symbolic dimension to the resulting id.
        ssSetCompInputPortSymbolicDimsId(S, portIndex, inputDimsId);
    }
}
#endif

Related Topics

• Implement Symbolic Dimensions for Array Sizes in Generated Code

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