/* Compute pi by numerical integration, RMA version */
/* this code is based on code from section 2.3.2 from Using MPI-2 book */
#include "mpi.h"
#include <math.h>
#include <stdio.h>
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);
}

MPI_Win_fence(0, nwin);
while (1) {
    if (myid == 0) {
        printf("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)
            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;
}