| 1 | = Ex15.c = |
| 2 | A parallel version of ex4.c |
| 3 | {{{#!C |
| 4 | /* |
| 5 | Large Scale Computing |
| 6 | Heat/Mass Transfer |
| 7 | ex15.c : Red-Black Gauss-Seidel |
| 8 | */ |
| 9 | #include<stdio.h> |
| 10 | #include<stdlib.h> |
| 11 | #include<math.h> |
| 12 | |
| 13 | int main(int argc, char **argv){ |
| 14 | double a,b,d; |
| 15 | double *phi; |
| 16 | double w; |
| 17 | double *rhs; |
| 18 | double dx; |
| 19 | double err,merr,share_err; |
| 20 | double tol = 1.0e-8; |
| 21 | int i,num,itc; |
| 22 | int nthreads; |
| 23 | FILE *fp; |
| 24 | |
| 25 | if (argc < 5){ |
| 26 | printf("Usage:%s [NUM] [A] [B] [D]\n",argv[0]); |
| 27 | exit(-1); |
| 28 | } |
| 29 | |
| 30 | /* set parameters */ |
| 31 | num = atoi(argv[1]); |
| 32 | a = atof(argv[2]); |
| 33 | b = atof(argv[3]); |
| 34 | d = atof(argv[4]); |
| 35 | |
| 36 | printf("num=%d A=%e B=%e D=%e\n",num,a,b,d); |
| 37 | |
| 38 | /* Memory Allocation and Check*/ |
| 39 | phi = (double *)calloc(num, sizeof(double)); |
| 40 | if (phi == (double *)NULL){ |
| 41 | printf("Memory Allocation Failed\n"); |
| 42 | exit(-1); |
| 43 | } |
| 44 | |
| 45 | rhs = (double *)calloc(num, sizeof(double)); |
| 46 | if (rhs == (double *)NULL){ |
| 47 | printf("Memory Allocation Failed\n"); |
| 48 | exit(-1); |
| 49 | } |
| 50 | |
| 51 | /** Setup **/ |
| 52 | dx = 1.0 / (double)(num - 1); |
| 53 | for (i = 0 ; i < num ; i++){ |
| 54 | rhs[i] = -dx * dx / d * (dx * (double)i); |
| 55 | phi[i] = 0.0; |
| 56 | } |
| 57 | |
| 58 | /* Boundary Condition*/ |
| 59 | phi[0] = a; |
| 60 | phi[num-1] = b; |
| 61 | |
| 62 | /* Solve with Gauss-Seidel Method*/ |
| 63 | itc = 0; |
| 64 | while(1){ |
| 65 | share_err = 0.0; |
| 66 | |
| 67 | #pragma omp parallel private(merr,err,w) |
| 68 | { |
| 69 | nthreads = omp_get_num_threads(); |
| 70 | /* update phi & Check Convergence */ |
| 71 | merr = 0.0; |
| 72 | #pragma omp for /* Black (odd) */ |
| 73 | for (i = 1 ; i < (num - 1) ; i+=2){ |
| 74 | w = -0.5 * (rhs[i] - phi[i + 1] - phi[i - 1]); |
| 75 | err = fabs(w - phi[i]); |
| 76 | phi[i] = w; |
| 77 | if (merr < err) merr = err; |
| 78 | } |
| 79 | |
| 80 | #pragma omp barrier /* wait until all come here*/ |
| 81 | |
| 82 | #pragma omp for /* Red (even) */ |
| 83 | for (i = 2 ; i < (num - 1) ; i+=2){ |
| 84 | w = -0.5 * (rhs[i] - phi[i + 1] - phi[i - 1]); |
| 85 | err = fabs(w - phi[i]); |
| 86 | phi[i] = w; |
| 87 | if (merr < err) merr = err; |
| 88 | } |
| 89 | |
| 90 | #pragma omp critical |
| 91 | { |
| 92 | /* find max in whole threads */ |
| 93 | if (share_err < merr) share_err = merr; |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | itc++; |
| 98 | if (share_err < tol) break; |
| 99 | if ((itc % 10000) == 0) printf("itc=%d err=%e\n",itc,share_err); |
| 100 | } |
| 101 | |
| 102 | printf("Number of Iteration=%d\n",itc); |
| 103 | printf("Number of Threads=%d\n",nthreads); |
| 104 | |
| 105 | /* Output Result */ |
| 106 | fp = fopen("res.dat","w"); |
| 107 | if (fp == NULL){ |
| 108 | printf("File could not create\n"); |
| 109 | exit(-1); |
| 110 | } |
| 111 | |
| 112 | for (i = 0 ; i < num ; i++){ |
| 113 | fprintf(fp,"%e %e\n",dx * (double)i,phi[i]); |
| 114 | } |
| 115 | fclose(fp); |
| 116 | |
| 117 | /* END : Deallocate Memory */ |
| 118 | free(phi); |
| 119 | free(rhs); |
| 120 | printf("Done\n"); |
| 121 | } |
| 122 | }}} |