#include<stdio.h>
#include<stdlib.h>
#include <mpi.h>
#include <math.h>
double f(double a){
return(4.0 / (1.0 + a*a));
}
int main(int argc, char *argv[])
{
int n, rank, numprocs, i,rank_parts,rank_start;
double PI25DT = 3.141592653589793238462643;
double mypi, pi, h, sum, x;
MPI_Win nwin, piwin;
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
MPI_Win_create(&n, sizeof(int), 1, MPI_INFO_NULL,
MPI_COMM_WORLD, &nwin);
MPI_Win_create(&pi, sizeof(double), 1, MPI_INFO_NULL,
MPI_COMM_WORLD, &piwin);
while (1) {
if (rank == 0) {
printf("Enter the number of intervals: (0 quits)\n");
scanf("%d",&n);
pi = 0.0;
}
MPI_Win_fence(0, nwin);
if (rank != 0)
MPI_Get(&n, 1, MPI_INT, 0, 0, 1, MPI_INT, nwin);
MPI_Win_fence(0, nwin);
if (n == 0)
break;
else {
rank_parts=n/numprocs;
rank_start=rank*rank_parts;
h = 1.0 / (double) n;
sum = 0.0;
for (i = 0; i <= rank_parts; i++) {
x = h * ((double)(rank_start+i));
sum += f(x);
}
mypi = h * sum;
MPI_Win_fence( 0, piwin);
MPI_Accumulate(&mypi, 1, MPI_DOUBLE, 0, 0, 1, MPI_DOUBLE,
MPI_SUM, piwin);
MPI_Win_fence(0, piwin);
if (rank == 0)
printf("pi is approximately %.16f, Error is %.16f\n",
pi, fabs(pi - PI25DT));
}
}
MPI_Win_free(&nwin);
MPI_Win_free(&piwin);
MPI_Finalize();
return 0;
}
Runs