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Matlab/Simulink S-Function example: Square a number

The following simple S-Function examples squares the real input value and outputs the squared value.

square.cpp

#define S_FUNCTION_NAME square
#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, 1);  // Single input
    ssSetInputPortDirectFeedThrough(S, 0, 1); // Direct feedthrough

    if (!ssSetNumOutputPorts(S, 1)) return;
    ssSetOutputPortWidth(S, 0, 1); // 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
    real_T input = *uPtrs[0];
    *y = input * input;
}

// 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

all:
	mex square.cpp

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

Example usage:

Simulink Square SFunction

The output here is 64 because 8*8=64.