Mex-File issue : correlated gaussians

Hello, I wrote the following code in a MexFunction:

    void Gaussians(double *H, int N, double *W)
{
    /* computes the matrix multiplication H*R where H is a (N x N) matrix
     * and R is a (N x 1) gaussian vector */

    mxArray *rhs1[2], *rhs2[2], *lhs1[1], *lhs2[1];

    rhs1[0] = mxCreateDoubleScalar(N);
    rhs1[1] = mxCreateDoubleScalar(1);

    /* generates R = randn(N, 1) */
    mexCallMATLAB(1, lhs1, 2, rhs1, "randn");

    rhs2[0] = mxGetPr(H);
    rhs2[1] = lhs1[0];

    W = mxGetPr(lhs2[0]);

    /* computes H*R */
    mexCallMATLAB(1, lhs2, 2, rhs2, "mtimes");

}

There is no problem with the mex compilation but when I run the program, I get an "Acces violation" error and matlab crashes. I was not able to find where the problem comes from.

Thank you for your help

PS : I'm starting with C language and Mex-Files.

Answer 1

[Jan]

    rhs2[0] = mxGetPr(H);

On the left side you have pointer to an mxArray, on the right you try to get the pointer to the double data of an myArray, but the argument is a pointer to a double already. It is surprising that the compiler accepts this. The next line contains similar problems:

    rhs2[1] = lhs1[0];

What do you want to achieve?