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/*
* Copyright (C) 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;
}
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