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
main()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