1 | /* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */ |
---|

2 | /* |
---|

3 | * (C) 2001 by Argonne National Laboratory. |
---|

4 | * See COPYRIGHT in top-level directory. |
---|

5 | */ |
---|

6 | |
---|

7 | #include "mpi.h" |
---|

8 | #include <stdio.h> |
---|

9 | #include <math.h> |
---|

10 | |
---|

11 | double f(double); |
---|

12 | |
---|

13 | double f(double a) |
---|

14 | { |
---|

15 | return (4.0 / (1.0 + a*a)); |
---|

16 | } |
---|

17 | |
---|

18 | int main(int argc,char *argv[]) |
---|

19 | { |
---|

20 | int n, myid, numprocs, i; |
---|

21 | double PI25DT = 3.141592653589793238462643; |
---|

22 | double mypi, pi, h, sum, x; |
---|

23 | double startwtime = 0.0, endwtime; |
---|

24 | int namelen; |
---|

25 | char processor_name[MPI_MAX_PROCESSOR_NAME]; |
---|

26 | |
---|

27 | MPI_Init(&argc,&argv); |
---|

28 | MPI_Comm_size(MPI_COMM_WORLD,&numprocs); |
---|

29 | MPI_Comm_rank(MPI_COMM_WORLD,&myid); |
---|

30 | MPI_Get_processor_name(processor_name,&namelen); |
---|

31 | |
---|

32 | fprintf(stdout,"Process %d of %d is on %s\n", |
---|

33 | myid, numprocs, processor_name); |
---|

34 | fflush(stdout); |
---|

35 | |
---|

36 | n = 10000; /* default # of rectangles */ |
---|

37 | if (myid == 0) |
---|

38 | startwtime = MPI_Wtime(); |
---|

39 | |
---|

40 | MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD); |
---|

41 | |
---|

42 | h = 1.0 / (double) n; |
---|

43 | sum = 0.0; |
---|

44 | /* A slightly better approach starts from large i and works back */ |
---|

45 | for (i = myid + 1; i <= n; i += numprocs) |
---|

46 | { |
---|

47 | x = h * ((double)i - 0.5); |
---|

48 | sum += f(x); |
---|

49 | } |
---|

50 | mypi = h * sum; |
---|

51 | |
---|

52 | MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD); |
---|

53 | |
---|

54 | if (myid == 0) { |
---|

55 | endwtime = MPI_Wtime(); |
---|

56 | printf("pi is approximately %.16f, Error is %.16f\n", |
---|

57 | pi, fabs(pi - PI25DT)); |
---|

58 | printf("wall clock time = %f\n", endwtime-startwtime); |
---|

59 | fflush(stdout); |
---|

60 | } |
---|

61 | |
---|

62 | MPI_Finalize(); |
---|

63 | return 0; |
---|

64 | } |
---|