AMS250

davidparks21

May 10th, 2016

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#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
int main(int argc, char* argv[])
{
// Setup
long num_iterations = atoi(argv[1]);
long int num_in_circle = 0;
double sum_pi_approximations = 0;
int rank, size;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
printf("Hello, world! I am process %d of %d, with id %d\n", rank + 1, size, rank); fflush(stdout);
MPI_Status mpistatus;
// An array storing the random seeds for each rank in the cluster
int *random_seeds = (int*)malloc(sizeof(int*)*size);
// Worker rank 0 will generate random seeds and send them to other cluster ranks, other cluster ranks receive the random seeds
srand((unsigned)time(NULL));
if (rank == 0) {
for (int i = 0; i < size; i++) {
random_seeds[i] = rand();
}
}
// Broadcast / receive random seeds
MPI_Bcast(random_seeds, size, MPI_INT, 0, MPI_COMM_WORLD);
// Seed local rng with its appropriate value
printf(" Rank %d local random seed is: %i\n", rank, random_seeds[rank]);
srand(random_seeds[rank]);
free(random_seeds);
// Compute local approximation of PI using dartboard method
for (int i = 0; i < num_iterations; i++) {
double r1 = ((double)rand() / (double)RAND_MAX);
double r2 = ((double)rand() / (double)RAND_MAX);
if( sqrt( pow(r1-0.5, 2) + pow(r2-0.5, 2) ) <= 0.5 ) {
//The dart is in the circle, count it
num_in_circle++;
}
}
// Compute the local pi approximation
double local_pi_approximation = (float)num_in_circle / (float)num_iterations * 4;
printf(" Local pie approximation %f\n Num in cicrcle / num iterations %i / %i\n", local_pi_approximation, num_in_circle, num_iterations);
// Merge the approximations from all ranks
MPI_Reduce(&local_pi_approximation, &sum_pi_approximations, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
// Rank 0 outputs results
if (rank == 0) printf( "Cluster approximation of pie using %i MPI processes: %.53f", size, sum_pi_approximations / size ); fflush(stdout);
MPI_Finalize();
return 0;
}

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