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/*
* Copyright (C) by Argonne National Laboratory
* See COPYRIGHT in top-level directory
*/
#include "mpi.h"
#include "stdio.h"
#include <math.h>
/* From Using MPI-2 */
int main(int argc, char *argv[])
{
int n, myid, numprocs, i;
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, &myid);
if (myid == 0) {
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);
} else {
MPI_Win_create(MPI_BOTTOM, 0, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &nwin);
MPI_Win_create(MPI_BOTTOM, 0, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &piwin);
}
while (1) {
if (myid == 0) {
fprintf(stdout, "Enter the number of intervals: (0 quits) ");
fflush(stdout);
scanf("%d", &n);
pi = 0.0;
}
MPI_Win_fence(0, nwin);
if (myid != 0)
MPI_Get(&n, 1, MPI_INT, 0, 0, 1, MPI_INT, nwin);
MPI_Win_fence(0, nwin);
if (n == 0)
break;
else {
h = 1.0 / (double) n;
sum = 0.0;
for (i = myid + 1; i <= n; i += numprocs) {
x = h * ((double) i - 0.5);
sum += (4.0 / (1.0 + x * 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 (myid == 0) {
fprintf(stdout, "pi is approximately %.16f, Error is %.16f\n",
pi, fabs(pi - PI25DT));
fflush(stdout);
}
}
}
MPI_Win_free(&nwin);
MPI_Win_free(&piwin);
MPI_Finalize();
return 0;
}
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