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/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */
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/*
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* (C) 2001 by Argonne National Laboratory.
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* See COPYRIGHT in top-level directory.
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*/
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#include "mpi.h"
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#include <stdio.h>
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#include <math.h>
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double f(double);
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double f(double a)
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{
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return (4.0 / (1.0 + a * a));
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}
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int main(int argc, char *argv[])
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{
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int n, myid, numprocs, i;
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double PI25DT = 3.141592653589793238462643;
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double mypi, pi, h, sum, x;
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double startwtime = 0.0, endwtime;
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int namelen;
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char processor_name[MPI_MAX_PROCESSOR_NAME];
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MPI_Init(&argc, &argv);
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MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
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MPI_Comm_rank(MPI_COMM_WORLD, &myid);
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MPI_Get_processor_name(processor_name, &namelen);
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fprintf(stdout, "Process %d of %d is on %s\n", myid, numprocs, processor_name);
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fflush(stdout);
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n = 10000; /* default # of rectangles */
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if (myid == 0)
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startwtime = MPI_Wtime();
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MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
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h = 1.0 / (double) n;
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sum = 0.0;
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/* A slightly better approach starts from large i and works back */
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for (i = myid + 1; i <= n; i += numprocs) {
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x = h * ((double) i - 0.5);
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sum += f(x);
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}
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mypi = h * sum;
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MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
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if (myid == 0) {
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endwtime = MPI_Wtime();
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printf("pi is approximately %.16f, Error is %.16f\n", pi, fabs(pi - PI25DT));
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printf("wall clock time = %f\n", endwtime - startwtime);
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fflush(stdout);
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}
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MPI_Finalize();
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return 0;
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}
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