Lapacke in level-2 C S-function

Hi, I would like to implement the function dpotrs from LAPACKE in the level-2 C S-function. However, whenever I make a call to this function, matlab/simulink gives an internal error. The S-function runs when I put dpotrs in comments (and thus I just copy the input B). My mdlOutputs looks like the following:

static void mdlOutputs(SimStruct *S, int_T tid)
{
    int_T *dimsB = ssGetInputPortDimensions(S, 1);
    real_T n     = dimsB[0];
    real_T m     = dimsB[1];
    real_T q;
    real_T *C;
    
    const real_T *A   =   ssGetInputPortRealSignal(S,0);
    const real_T *B   =   ssGetInputPortRealSignal(S,1);
    real_T       *X   =  ssGetOutputPortRealSignal(S,0);
    memcpy( X, B, (size_t)m*(size_t)n*sizeof(real_T)); 
    
    /* Solve system */
    dpotrs("U", &n, &m, A, &n, X, &n, &q);
    if (q < 0) ssSetErrorStatus(S,"Error: illegal input to solve_chol");
}

I am able to compile the C code with:

mex -R2018a solve_chol_sfun.c -lmwlapack

I'm quite certain that the dimensions of the variables are correct. Any suggestions?

Answer 1

[James Tursa]

According to the interface listed here and the link you list above:

http://www.netlib.no/netlib/lapack/double/dpotrs.f

The n, m, and q arguments should be integer type. Typically, when linking with the MATLAB supplied BLAS and LAPACK libraries, this means mwSignedIndex. So try:

    mwSignedIndex n     = dimsB[0];
    mwSignedIndex m     = dimsB[1];
    mwSignedIndex q;

[Wouter van Dijk]

Spot on, this works!