Handle Complex Data in C MEX File - MATLAB & Simulink (original) (raw)

The example convec.c takes two complex row vectors and convolves them. The MEX file uses functions in the C Matrix API.

Create Source File

The following statements document the MEX function.

/*=========================================================

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[] ) { return; }

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 outputmxArray.

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 pointerplhs[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:

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

mxGetComplexDoubles

Topics