/* -*- 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>

double f(double);

double f(double a)

{

    return (4.0 / (1.0 + a*a));

}

int main(int argc,char *argv[])

{

    int    n, myid, numprocs, i;

    double PI25DT = 3.141592653589793238462643;

    double mypi, pi, h, sum, x;

    double startwtime = 0.0, endwtime;

    int    namelen;

    char   processor_name[MPI_MAX_PROCESSOR_NAME];

    MPI_Init(&argc,&argv);

    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);

    MPI_Comm_rank(MPI_COMM_WORLD,&myid);

    MPI_Get_processor_name(processor_name,&namelen);

    fprintf(stdout,"Process %d of %d is on %s\n",

	    myid, numprocs, processor_name);

    fflush(stdout);

    n = 10000;			/* default # of rectangles */

    if (myid == 0)

	startwtime = MPI_Wtime();

    MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);

    h   = 1.0 / (double) n;

    sum = 0.0;

    /* A slightly better approach starts from large i and works back */

    for (i = myid + 1; i <= n; i += numprocs)

    {

	x = h * ((double)i - 0.5);

	sum += f(x);

    }

    mypi = h * sum;

    MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);

    if (myid == 0) {

	endwtime = MPI_Wtime();

	printf("pi is approximately %.16f, Error is %.16f\n",

	       pi, fabs(pi - PI25DT));

	printf("wall clock time = %f\n", endwtime-startwtime);	       

	fflush(stdout);

    }

    MPI_Finalize();

    return 0;

}