Naotoshi Seo

Matlab C Library Call Matlab Built-In Functions

Table of Contents

Syntax Arguments Returns Examples

Use mexCallMatlab functions.

Syntax

#include "mex.h"
int mexCallMATLAB(int nlhs, mxArray *plhs[], int nrhs,
 mxArray *prhs[], const char *name);

Arguments

nlhs

Number of desired output arguments. This value must be less than or equal to 50.

plhs

Array of pointers to mxArrays. The called command puts pointers to the resultant mxArrays into plhs and allocates dynamic memory to store the resultant mxArrays. By default, MATLAB automatically deallocates this dynamic memory when you clear the MEX-file. However, if heap space is at a premium, you may want to call mxDestroyArray as soon as you are finished with the mxArrays that plhs points to.

nrhs

Number of input arguments. This value must be less than or equal to 50.

prhs

Array of pointers to input arguments.

name

Character string containing the name of the MATLAB built-in, operator, M-file, or MEX-file that you are calling. If name is an operator, just place the operator inside a pair of single quotes, for example, '+'.

Returns

0 if successful, and a nonzero value if unsuccessful.

Examples

/*=================================================================
 * mexcallmatlab.c
 *
 * mexcallmatlab takes no inputs.  This routine first forms and
 * displays the following matrix (in MATLAB notation):
 *
 *      hankel(1:4,4:-1:1) + sqrt(-1)*toeplitz(1:4,1:4)
 *
 * Next it finds the eigenvalues and eigenvectors (using the MATLAB
 * function EIG), and displays the eigenvalue matrix.  Then it
 * calculates the inverse of the eigenvalues to demonstrate manipulation
 * of MATLAB results and how to deal with complex arithemetic.  Finally,
 * the program displays the inverse values.
 *
 * Copyright 1984-2006 The MathWorks, Inc.
 * $Revision: 1.11.6.2 $
 *================================================================*/

#include <math.h>
#include "mex.h"

#define XR(i,j) xr[i+4*j]
#define XI(i,j) xi[i+4*j]

static void fill_array( double	*xr, double  *xi)
{
    double tmp;
    int i,j,jj;
    /* Remember, MATLAB stores matrices in their transposed form,
       i.e., columnwise, like FORTRAN. */
    
/* Fill real and imaginary parts of array. */
    for (j = 0; j < 4; j++) {
	for (i = 0; i <= j; i++) {
	    XR(i,j) = 4 + i - j;
	    XR(j,i) = XR(i,j);
	    XI(i,j) = j - i + 1;
	    XI(j,i) = XI(i,j);
	}
    }
    /* Reorder columns of xr. */
    for (j = 0; j < 2; j++) {
	for (i = 0; i < 4; i++) {
	    tmp = XR(i,j);
	    jj = 3 - j;
	    XR(i,j) = XR(i,jj);
	    XR(i,jj) = tmp;
	}
    }
}

/* Invert diagonal elements of complex matrix of order 4 */
static void invertd( double *xr, double *xi )
{
    double tmp;
    double *rx, *ix;
    int i;
    
    rx = xr;
    ix = xi;
    
    /* I know diagnonal elements of a 4 X 4 are 1:5:16 */
    for (i = 0; i < 16; i += 5, rx += 5, ix += 5) {
	tmp = *rx * *rx + *ix * *ix;
	*rx = *rx / tmp;
	*ix = - *ix / tmp;
    }		
}

void 
mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray	*prhs[])
{
    mwSize m, n;
    mxArray *lhs[2], *x;
    (void) prhs;           /* unused parameter */
    
    m = n = 4;
    
    /* Check for proper number of input and output arguments */    
    if (nrhs != 0) {
	mexErrMsgTxt("No input arguments required.");
    } 
    if(nlhs > 1){
	mexErrMsgTxt("Too many output arguments.");
    } 
    
    /* Allocate x matrix */
    x =  mxCreateDoubleMatrix(m, n, mxCOMPLEX);
    
    /* create values in some arrays -- remember, MATLAB stores matrices
       column-wise */
    fill_array(mxGetPr(x), mxGetPi(x));
    
    /* print out initial matrix */
    mexCallMATLAB(0,NULL,1, &x, "disp");
    
    /* calculate eigenvalues and eigenvectors */
    mexCallMATLAB(2, lhs, 1, &x, "eig");
    
    /* print out eigenvalue matrix */
    mexCallMATLAB(0,NULL,1, &lhs[1], "disp");
    
    /* take inverse of complex eigenvalues, just on diagonal */
    invertd(mxGetPr(lhs[1]), mxGetPi(lhs[1]));
    
    /* and print these out */
    mexCallMATLAB(0,NULL,1, &lhs[1], "disp");
    
    /* Free allocated matrices */
    mxDestroyArray(x);
    mxDestroyArray(lhs[1]);
    plhs[0] = lhs[0];
}