#include "mpi.h"
#include <math.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);
    }
    while (1) {
        if (myid == 0) {
            printf("Enter the number of intervals: (0 quits) ");
            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;
}
