I have a question.. I tried to improve a well known program algorithm in C, FOX algorithm for matrix multiplication.. relative link without openMP: (http://web.mst.edu/~ercal/387/MPI/ppmpi_c/chap07/fox.c). The initial program had only MPI and I tried to insert openMP in the matrix multiplication method, in order to improve the time of computation: (This program runs in a cluster and computers have 2 cores, thus I created 2 threads.) The problem is that there is no difference of time, with and without openMP. I observed that using openMP sometimes, time is equivalent or greater than the time without openMP. I tried to multiply two 600x600 matrices.

void Local_matrix_multiply(
         LOCAL_MATRIX_T*  local_A  /* in  */,
         LOCAL_MATRIX_T*  local_B  /* in  */, 
         LOCAL_MATRIX_T*  local_C  /* out */) {
    int i, j, k;
     chunk = CHUNKSIZE; // 100


#pragma omp parallel shared(local_A, local_B, local_C, chunk, nthreads) private(i,j,k,tid) num_threads(2) 
   {  
        /*
    tid = omp_get_thread_num();
    if(tid == 0){
    nthreads = omp_get_num_threads();

    printf("O Pollaplasiamos pinakwn ksekina me %d threads\n", nthreads);
    }
    printf("Thread %d use the matrix: \n", tid);
    */

     #pragma omp for schedule(static, chunk)
    for (i = 0; i < Order(local_A); i++)
        for (j = 0; j < Order(local_A); j++)
            for (k = 0; k < Order(local_B); k++)
                Entry(local_C,i,j) = Entry(local_C,i,j) 
                    + Entry(local_A,i,k)*Entry(local_B,k,j);



} //end pragma omp parallel


}  /* Local_matrix_multiply */