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mpiPICyclic.c
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mpiPICyclic.c
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#include <mpi.h>
#include <stdio.h>
double f (double x) {
return 4.0 / ( 1 + x * x);
}
int main (int argc, char** argv) {
double PI25DT = 3.141592653589793238462643;
MPI_Init (&argc, &argv);
int myid;
int numprocs;
int namelen;
char myname[MPI_MAX_PROCESSOR_NAME];
MPI_Comm_size (MPI_COMM_WORLD, &numprocs);
MPI_Comm_rank (MPI_COMM_WORLD, &myid);
MPI_Get_processor_name (myname, &namelen);
printf ("Hello World from process %d (%s) out of %d\n", myid, myname, numprocs);
// compute PI
int N;
if (myid == 0) {
printf ("enter num intervals on proc 0\n");
scanf ("%d", &N);
}
MPI_Barrier (MPI_COMM_WORLD);
double time = MPI_Wtime ();
MPI_Bcast (&N, 1, MPI_INT, 0, MPI_COMM_WORLD);
double mypi = 0.0;
int i;
for ( i = myid; i < N; i += numprocs) {
// width of each rectangular section
double w = 1.0 / (double)N;
// mid point of the rectangle
double x_i = ((double)i + 0.5) / (double)N;
// height of the curve at the mid point
double h = f(x_i);
// area of the rectangle
mypi += w * h;
}
printf ("proc %d contributed %10.25f to pi\n", myid, mypi);
double pi = 0.0;
MPI_Reduce (&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
MPI_Barrier (MPI_COMM_WORLD);
if (myid == 0) {
printf ("Computed value of pi = %10.25f\n", pi);
printf ("Actual value of pi = %10.25f\n", PI25DT);
double err = (PI25DT - pi) / PI25DT;
printf ("Relative error = %g\n", err);
}
time = MPI_Wtime () - time;
printf ("Time taken by proc %d is %g\n", myid, time);
MPI_Finalize();
}