AMS250

#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;
}