This is machine translation

Translated by Microsoft
Mouseover text to see original. Click the button below to return to the English version of the page.

Note: This page has been translated by MathWorks. Click here to see
To view all translated materials including this page, select Country from the country navigator on the bottom of this page.

Handle Complex Data

This example convec.c takes two complex row vectors and convolves them. The example assumes a basic understanding of MEX files as described in Create C Source MEX File.

Create Source File

The following statements document the MEX function.

 * convec.c
 * example for passing complex data from MATLAB to C and back again
 * convolves  two complex input vectors
 * This is a MEX-file for MATLAB.
 * Copyright 1984-2017 The MathWorks, Inc.

Create Gateway Routine and Verify Input and Output Parameters

The following statements add the C/C++ header file mex.h and creates the mexFunction entry point.

#include "mex.h"

/* The gateway routine. */
void mexFunction( int nlhs, mxArray *plhs[],
                  int nrhs, const mxArray *prhs[] )

The following statements validate the number of parameters.

    /* check for the proper number of arguments */
    if(nrhs != 2)
      mexErrMsgIdAndTxt( "MATLAB:convec:invalidNumInputs",
              "Two inputs required.");
    if(nlhs > 1)
      mexErrMsgIdAndTxt( "MATLAB:convec:maxlhs",
              "Too many output arguments.");

The following statement verifies that the input arguments are row vectors.

    /*Check that both inputs are row vectors*/
    if( mxGetM(prhs[0]) != 1 || mxGetM(prhs[1]) != 1 )
      mexErrMsgIdAndTxt( "MATLAB:convec:inputsNotVectors",
              "Both inputs must be row vectors.");

The following statement verifies that the input arguments are complex.

    /* Check that both inputs are complex*/
    if( !mxIsComplex(prhs[0]) || !mxIsComplex(prhs[1]) )
      mexErrMsgIdAndTxt( "MATLAB:convec:inputsNotComplex",
              "Inputs must be complex.\n");

Create Output mxArray

The following statements define the parameters for creating the output mxArray.

    size_t rows, cols;
    size_t nx, ny;

    /* get the length of each input vector */
    nx = mxGetN(prhs[0]);
    ny = mxGetN(prhs[1]);

    rows = 1; 
    cols = nx + ny - 1;

The following statement creates an array and sets the output pointer plhs[0] to it.

    plhs[0] = mxCreateDoubleMatrix( (mwSize)rows, (mwSize)cols, mxCOMPLEX);

Create Computational Routine

The following statements define convec, the computational routine.

void convec(mxArray * x, mxArray * y, mxArray * z,
            size_t nx, size_t ny)
    mwSize i,j;

    /* get pointers to the complex arrays */
    mxComplexDouble * xc = mxGetComplexDoubles(x);
    mxComplexDouble * yc = mxGetComplexDoubles(y);
    mxComplexDouble * zc = mxGetComplexDoubles(z);
    zc[0].real = 0;
    zc[0].imag = 0;
    /* perform the convolution of the complex vectors */
    for(i=0; i<nx; i++) {
        for(j=0; j<ny; j++) {
            zc[i+j].real =
            zc[i+j].real + xc[i].real * yc[j].real - xc[i].imag * yc[j].imag;

            zc[i+j].imag =
            zc[i+j].imag + xc[i].real * yc[j].imag + xc[i].imag * yc[j].real;

Call convec

The following statement calls the computational routine.

    convec(prhs[0], prhs[1], plhs[0], nx, ny);

Build and Test

At the MATLAB® command prompt type:

mex -R2018a convec.c

Test the MEX file.

x = [3.000 - 1.000i, 4.000 + 2.000i, 7.000 - 3.000i];
y = [8.000 - 6.000i, 12.000 + 16.000i, 40.000 - 42.000i];
z = convec(x,y)
z =
   1.0e+02 *

Columns 1 through 4 

0.1800 - 0.2600i 0.9600 + 0.2800i 1.3200 - 1.4400i 3.7600 - 0.1200i

Column 5 

1.5400 - 4.1400i

Compare the results with the built-in MATLAB function conv.


See Also

Related Topics