1 /******************************************************************************
2 * OpenMP Example - Matrix-vector multiplication - C/C++ Version
3 * FILE: omp_matvec.c
4 * DESCRIPTION:
5 *   This example multiplies all row i elements of matrix A with vector
6 *   element b(i) and stores the summed products in vector c(i).  A total is
7 *   maintained for the entire matrix.  Performed by using the OpenMP loop
8 *   work-sharing construct.  The update of the shared global total is
9 *   serialized by using the OpenMP critical directive.
10 * SOURCE: Blaise Barney  5/99
11 * LAST REVISED:
12 ******************************************************************************/
13 
14 #include <omp.h>
15 #include <stdio.h>
16 #define SIZE 10
17 
18 
19 main ()
20 {
21 
22 float A[SIZE][SIZE], b[SIZE], c[SIZE], total;
23 int i, j, tid;
24 
25 /* Initializations */
26 total = 0.0;
27 for (i=0; i < SIZE; i++)
28   {
29   for (j=0; j < SIZE; j++)
30     A[i][j] = (j+1) * 1.0;
31   b[i] = 1.0 * (i+1);
32   c[i] = 0.0;
33   }
34 printf("\nStarting values of matrix A and vector b:\n");
35 for (i=0; i < SIZE; i++)
36   {
37   printf("  A[%d]= ",i);
38   for (j=0; j < SIZE; j++)
39     printf("%.1f ",A[i][j]);
40   printf("  b[%d]= %.1f\n",i,b[i]);
41   }
42 printf("\nResults by thread/row:\n");
43 
44 /* Create a team of threads and scope variables */
45 #pragma omp parallel shared(A,b,c,total) private(tid,i)
46   {
47   tid = omp_get_thread_num();
48 
49 /* Loop work-sharing construct - distribute rows of matrix */
50 #pragma omp for private(j)
51   for (i=0; i < SIZE; i++)
52     {
53     for (j=0; j < SIZE; j++)
54       c[i] += (A[i][j] * b[i]);
55 
56     /* Update and display of running total must be serialized */
57     #pragma omp critical
58       {
59       total = total + c[i];
60       printf("  thread %d did row %d\t c[%d]=%.2f\t",tid,i,i,c[i]);
61       printf("Running total= %.2f\n",total);
62       }
63 
64     }   /* end of parallel i loop */
65 
66   } /* end of parallel construct */
67 
68 printf("\nMatrix-vector total - sum of all c[] = %.2f\n\n",total);
69 
70   return 0;
71 }
72 
73