M-M_omp_sparse.c

/**
 * @author Rohin Arora
 * @email rohinarora07@gmail.com
 * @create date 2020-02-25
 * @modify date 2020-02-25
 *
 * Sparse Matrix multiplication with OMP 
 */
#include <stdio.h>
#include<stdlib.h>
#include <time.h>
#define M 512 

double CLOCK() {
        struct timespec t;
        clock_gettime(CLOCK_MONOTONIC,  &t);
        return (t.tv_sec * 1000)+(t.tv_nsec*1e-6);
}

int main(int argc, char **argv)
{
    int i,j,k;
    double start, finish, total, sum;
    float  a[M][M], b[M][M], c[M][M];


/* Initialize a, b and c */
    for (i=0; i<M; i++)
       for (j=0; j<M; j++)
          {
            if ((i+j)%7 == 0)
             a[i][j] = 2.;
            else a[i][j] = 0.;
	  }

    for (i=0; i<M; i++)
       for (j=0; j<M; j++)
             b[i][j] = (i/3)+(j/5); 

    for (i=0; i<M; i++)
       for (j=0; j<M; j++)
           c[i][j] = 0.;

/* Start timing */
    start = CLOCK();

/* This is the only portion of the code you should modify to improve performance. */

    // A is sparse, B is dense...
    // Any new experiment will only change the position and value of
    // non zeros, but follow a similar pattern...
    // Thus collect these values and using them later in loop iteration
    double nz_val;
    int nz_i;
    int nz_k;
    for (i=1; i<M; i++){
      for (k=1; k<M; k++) {
        if (a[i][k] != 0) {
          nz_val = a[i][k];
          nz_i = i;
          nz_k = k;
          break;
        }
      }
      break;
    }
    const int nz_pattern = nz_i + nz_k;


#pragma omp parallel private(i,j,k) firstprivate(nz_pattern,nz_val) shared(c,b) default(none)
{
    #pragma omp for
    for (i=0; i<M; i++){
      for (k=0; k<M; k++) {
        if ((i+k)%nz_pattern == 0) { // only multiply the important values
          for (j=0; j<M; j++) {
            c[i][j] += nz_val*b[k][j];
          }
        }
      }
    }
}

    finish = CLOCK();
/* End timing */
    total = finish - start;
    printf("Time for the loop = %f\n", total);
    printf("The value of c[%d][%d] = %4.2f\n", 0, 0, c[0][0]);
    printf("The value of c[%d][%d] = %4.2f\n", 31, 32, c[31][32]);
    printf("The value of c[%d][%d] = %4.2f\n", 510, 0, c[510][0]);
    printf("The value of c[%d][%d] = %4.2f\n", 511, 511, c[511][511]);

    return 0;
}