Error when using openmp 'collapse' directive in matlab mex

Hi,

I am trying to optimize the code for matrix multiplication in a mex file with openmp. The code is given below.

void MatrixMultiply(double *in1,double *in2,double *out,int M, int N, int P)

{

/* Description: multiplies a MxN matrix with a NxP matrix */

int i,j,k;
omp_set_num_threads(2);

#pragma omp parallel for schedule(static) shared(in1,in2,out,M,N,P) private(i,j,k) 

   for (i= 0; i < M; i++) {

     for (j = 0; j < P; j++) {

         out[M*j + i] = 0;            

         for (k = 0; k < N; k++) {

             out[M*j + i] += in1[k*M + i]*in2[j*N + k]; 

         }
      }
   }
    return;
   }

However, when I change the directive to "#pragma omp parallel for collapse(3) schedule(static) shared(in1,in2,out,M,N,P) private(i,j,k) " I get an error - "error C3005: 'collapse' : unexpected token encountered on OpenMP 'parallel for' directive"

Any help in resolving this error would be appreciated.

Thanks!

Answer 1

[James Tursa]

Does your compiler support the collapse directive? What compiler are you using?

[Ajay Iyer]

I am using the Microsoft Visual C/C++ 2010 (Professional) compiler.

[James Tursa]

I think MSVC 2010 only supports OpenMP 2.0, and the collapse directive was introduced in OpenMP 3.0.

[Ajay Iyer]

Switching to gcc instead of MSVC fixed the problem. Thanks!