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- Timestamp:
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Jul 24, 2008, 12:06:13 PM (16 years ago)
- Author:
-
wade
- Comment:
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--
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2 | 2 | {{{ |
3 | 3 | /* Program: |
4 | | * mpich_example 內建範例,計算 pi 。 |
| 4 | * 由使用者輸入一整數,再由 root node 將些整數發送給底下 nodes, |
| 5 | * 每個 nodes 將收到的整數印出。 |
5 | 6 | * History: |
6 | | * 2008-04-11 BETA |
7 | | * 2008-06-19 增加可重複輸入欲計算之精準度 |
8 | | * 2008-06-23 加入 MPI_Barrier 以確保每個 node 在接受 n 後才執行 |
9 | | * / |
| 7 | * 2008-07-24 BETA |
| 8 | */ |
10 | 9 | |
11 | | #include "mpi.h" |
| 10 | |
12 | 11 | #include <stdio.h> |
13 | | #include <math.h> |
14 | | #include <time.h> |
| 12 | #include <mpi.h> |
| 13 | main (int argc, char **argv) |
| 14 | { |
| 15 | int i = 0; |
| 16 | int myid, numprocs; |
| 17 | MPI_Init(&argc, &argv); |
| 18 | MPI_Comm_size(MPI_COMM_WORLD, &numprocs); |
| 19 | MPI_Comm_rank(MPI_COMM_WORLD, &myid); |
15 | 20 | |
16 | | double f( double ); |
17 | | double f( double a ) |
18 | | { |
19 | | return (4.0 / (1.0 + a*a)); |
20 | | } |
| 21 | /* 這邊先印出所有 nodes 的整數 i 初始狀態 */ |
| 22 | printf("[Node %d] i = %d \n", myid, i); |
21 | 23 | |
22 | | int main( int argc, char *argv[]) |
23 | | { |
24 | | int done = 0, n, myid, numprocs, i=0; |
25 | | double PI25DT = 3.141592653589793238462643; |
26 | | double mypi, pi, h, sum, x; |
27 | | double startwtime = 0.0, endwtime; |
28 | | int namelen; |
29 | | char processor_name[MPI_MAX_PROCESSOR_NAME]; |
30 | | MPI_Init(&argc,&argv); |
31 | | MPI_Comm_size(MPI_COMM_WORLD,&numprocs); |
32 | | MPI_Comm_rank(MPI_COMM_WORLD,&myid); |
33 | | MPI_Get_processor_name(processor_name,&namelen); |
34 | | fprintf(stderr,"Process %d on %s\n", |
35 | | myid, processor_name); |
36 | | n = 0; |
37 | | while (!done) |
38 | | { |
39 | | /* 由 node 0 將使用者輸入的值送給其它的 node */ |
40 | | if (myid == 0) |
41 | | { |
42 | | printf("Enter the number of intervals: (0 quits) "); |
43 | | scanf("%d", &n); |
44 | | startwtime = MPI_Wtime(); |
45 | | } |
| 24 | /* node 0 (root) 會要求使用者輸入一個 INT 的整數 */ |
| 25 | if (myid == 0) |
| 26 | { |
| 27 | printf("Please input a INT number >>"); |
| 28 | scanf("%d", &i); |
| 29 | } |
46 | 30 | |
47 | | /* 這非常重要,所有的 node 必需在此同步,才可以收到使用者輸入的 n */ |
48 | | MPI_Barrier(MPI_COMM_WORLD); |
| 31 | /* node 0 (root) 會將所有 nodes 的 i 的值設為使用者所輸入的數 */ |
| 32 | MPI_Bcast(&i, 1, MPI_INT, 0, MPI_COMM_WORLD); |
49 | 33 | |
50 | | /* 將 n 送給其它的 node */ |
51 | | MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD); |
52 | | if (n == 0) |
53 | | done = 1; |
54 | | else |
55 | | { |
| 34 | /* 所有的 nodes 在此同步,以確認 node 0 (root) 已將 i 送給所有 nodes */ |
| 35 | MPI_Barrier(MPI_COMM_WORLD); |
56 | 36 | |
57 | | /* 此為計算 pi 的演算法 */ |
58 | | h = 1.0 / (double) n; |
59 | | sum = 0.0; |
60 | | for (i = myid + 1; i <= n; i += numprocs) |
61 | | { |
62 | | x = h * ((double)i - 0.5); |
63 | | sum += f(x); |
64 | | } |
65 | | mypi = h * sum; |
| 37 | printf("[Node %d] i = %d \n", myid, i); |
66 | 38 | |
67 | | /* 將算完的結果傳給 node 0 加總 */ |
68 | | MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD); |
69 | | if (myid == 0) |
70 | | { |
71 | | printf("pi is approximately %.16f, Error is %.16f\n", |
72 | | pi, fabs(pi - PI25DT)); |
73 | | endwtime = MPI_Wtime(); |
74 | | printf("wall clock time = %f\n", |
75 | | endwtime-startwtime); |
76 | | } |
77 | | } |
78 | | } |
79 | | MPI_Finalize(); |
80 | | return 0; |
| 39 | MPI_Finalize(); |
81 | 40 | } |
82 | 41 | }}} |