/* -*- Mode: C++; c-basic-offset:4 ; -*- *//*   *  (C) 2004 by Argonne National Laboratory. *      See COPYRIGHT in top-level directory. */#include "mpi.h"#include <iostream>#include <math.h>using namespace std;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);    numprocs = MPI::COMM_WORLD.Get_size();    myid     = MPI::COMM_WORLD.Get_rank();    MPI::Get_processor_name(processor_name,namelen);    cout << "Process " << myid << " of " << numprocs << " is on " <<	processor_name << endl;    n = 10000;			/* default # of rectangles */    if (myid == 0)	startwtime = MPI::Wtime();    MPI::COMM_WORLD.Bcast(&n, 1, MPI_INT, 0);    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::COMM_WORLD.Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0);    if (myid == 0) {	endwtime = MPI::Wtime();	cout << "pi is approximately " << pi << " Error is " <<	    fabs(pi - PI25DT) << endl;	cout << "wall clock time = " << endwtime-startwtime << endl;    }    MPI::Finalize();    return 0;}