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

/*

 *  (C) 2001 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;

}