Matlab/Simulink S-Function with vector input & output

The following S-function example demonstrates how to create an S-Function with vector input and output in Matlab/Simulink.

It accepts a 3-vector of real inputs
It will square the inputs element-wise
It will output a 3-vector of real outputs

In general, while writing vector I/O S-functions, remember that:

ssSetInputPortWidth(S, 0, n); or ssSetOutputPortWidth(S, 0, n); sets the number of elements in the vector to n. You must call this function in mdlInitializeSizes.
Input data is not given as continous array but as an array of pointers! To convert it to a vector:

square_vector.cpp

InputRealPtrsType uPtrs = ssGetInputPortRealSignalPtrs(S, 0);
// ...
std::array<double, 3> input = { *uPtrs[0], *uPtrs[1], *uPtrs[2] };

InputRealPtrsType uPtrs = ssGetInputPortRealSignalPtrs(S, 0);
// ...
std::array<double, 3> input = { *uPtrs[0], *uPtrs[1], *uPtrs[2] };

The output is given as a pointer to a continous vector

`square_vector.cpp`

example.cpp

#define S_FUNCTION_NAME square_vector
#define S_FUNCTION_LEVEL 2

#include "simstruc.h"

// Function: mdlInitializeSizes ==============================================
static void mdlInitializeSizes(SimStruct *S) {
    ssSetNumSFcnParams(S, 0);  // No parameters

    if (!ssSetNumInputPorts(S, 1)) return;
    ssSetInputPortWidth(S, 0, 3);  // Single input
    ssSetInputPortDirectFeedThrough(S, 0, 1); // Direct feedthrough

    if (!ssSetNumOutputPorts(S, 1)) return;
    ssSetOutputPortWidth(S, 0, 3); // Single output

    ssSetNumSampleTimes(S, 1);
    ssSetOptions(S, 0);
}

// Function: mdlInitializeSampleTimes =========================================
static void mdlInitializeSampleTimes(SimStruct *S) {
    ssSetSampleTime(S, 0, INHERITED_SAMPLE_TIME);
    ssSetOffsetTime(S, 0, 0.0);
}

// Function: mdlOutputs ======================================================
static void mdlOutputs(SimStruct *S, int_T tid) {
    // Get input signal
    InputRealPtrsType uPtrs = ssGetInputPortRealSignalPtrs(S, 0);

    // Get output signal
    real_T *y = ssGetOutputPortRealSignal(S, 0);

    // Square the input
    y[0] = *uPtrs[0] * *uPtrs[0];
    y[1] = *uPtrs[1] * *uPtrs[1];
    y[2] = *uPtrs[2] * *uPtrs[2];
}

// Function: mdlTerminate ====================================================
static void mdlTerminate(SimStruct *S) {
    // No termination tasks required
}

#ifdef  MATLAB_MEX_FILE
#include "simulink.c"      // MEX-file interface mechanism
#else
#include "cg_sfun.h"       // Code generation registration function
#endif

#define S_FUNCTION_NAME square_vector
#define S_FUNCTION_LEVEL 2

#include "simstruc.h"

// Function: mdlInitializeSizes ==============================================
static void mdlInitializeSizes(SimStruct *S) {
    ssSetNumSFcnParams(S, 0);  // No parameters

    if (!ssSetNumInputPorts(S, 1)) return;
    ssSetInputPortWidth(S, 0, 3);  // Single input
    ssSetInputPortDirectFeedThrough(S, 0, 1); // Direct feedthrough

    if (!ssSetNumOutputPorts(S, 1)) return;
    ssSetOutputPortWidth(S, 0, 3); // Single output

    ssSetNumSampleTimes(S, 1);
    ssSetOptions(S, 0);
}

// Function: mdlInitializeSampleTimes =========================================
static void mdlInitializeSampleTimes(SimStruct *S) {
    ssSetSampleTime(S, 0, INHERITED_SAMPLE_TIME);
    ssSetOffsetTime(S, 0, 0.0);
}

// Function: mdlOutputs ======================================================
static void mdlOutputs(SimStruct *S, int_T tid) {
    // Get input signal
    InputRealPtrsType uPtrs = ssGetInputPortRealSignalPtrs(S, 0);

    // Get output signal
    real_T *y = ssGetOutputPortRealSignal(S, 0);

    // Square the input
    y[0] = *uPtrs[0] * *uPtrs[0];
    y[1] = *uPtrs[1] * *uPtrs[1];
    y[2] = *uPtrs[2] * *uPtrs[2];
}

// Function: mdlTerminate ====================================================
static void mdlTerminate(SimStruct *S) {
    // No termination tasks required
}

#ifdef  MATLAB_MEX_FILE
#include "simulink.c"      // MEX-file interface mechanism
#else
#include "cg_sfun.h"       // Code generation registration function
#endif

`Makefile`

Makefile

all:
	mex square_vector.cpp

all:
	mex square_vector.cpp

How to use in Simulink

Step-by-step guide of how to add the S-function

Example usage:

Simulink Square Vector

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