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// -*- c++ -*-
//
// $Id: cxxpi.cc,v 1.4 2002/11/23 04:06:44 jsquyres Exp $
//
// Copyright (c) 2001-2002 The Trustees of Indiana University.
// All rights reserved.
// Copyright (c) 1998-2001 University of Notre Dame.
// All rights reserved.
// Copyright (c) 1994-1998 The Ohio State University.
// All rights reserved.
//
// This file is part of the LAM/MPI software package. For license
// information, see the LICENSE file in the top level directory of the
// LAM/MPI source distribution.
//
// $HEADER$
//
#include <math.h>
#include <iostream>
#include <mpi.h>
using namespace std;
int
main(int argc, char *argv[])
{
int n, rank, size, i;
double PI25DT = 3.141592653589793238462643;
double mypi, pi, h, sum, x;
MPI::Init(argc, argv);
size = MPI::COMM_WORLD.Get_size();
rank = MPI::COMM_WORLD.Get_rank();
// Prompt the user for how many iterations to use
if (rank == 0) {
//cout << "Enter the number of intervals: (0 quits)" << endl;
//cin >> n;
// Hardwired for simplicity. Feel free to uncomment the previous
// lines to get user input.
n = 10000;
}
// Broadcast the number of intervals
MPI::COMM_WORLD.Bcast(&n, 1, MPI::INT, 0);
if (n > 0) {
h = 1.0 / (double) n;
sum = 0.0;
for (i = rank + 1; i <= n; i += size) {
x = h * ((double)i - 0.5);
sum += (4.0 / (1.0 + x*x));
}
mypi = h * sum;
// Combine all the partial results
MPI::COMM_WORLD.Reduce(&mypi, &pi, 1, MPI::DOUBLE, MPI::SUM, 0);
if (rank == 0)
cout << "After " << n << " iterations, pi is approximately "
<< pi << ", Error is " << fabs(pi - PI25DT) << endl;
}
MPI::Finalize();
return 0;
}
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