pi3.cpp

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

int main(int argc, char* argv[]) {
    int rank, size;
    long long int i;
    static long long int num_steps = 1000000000;
    double step = 1.0 / (double)num_steps;
    double x, sum = 0.0, global_sum = 0.0;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    int chunk = num_steps / size;
    long long int start = rank * chunk;
    long long int end = (rank == size - 1) ? num_steps : start + chunk;

    // Synchronize all processes before starting the timer
    MPI_Barrier(MPI_COMM_WORLD);
    double t_start = MPI_Wtime();

    for (i = start; i < end; i++) {
        x = (i + 0.5) * step;
        sum += 4.0 / (1.0 + x * x);
    }

    MPI_Reduce(&sum, &global_sum, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
    double t_end = MPI_Wtime();

    if (rank == 0) {
        double pi = step * global_sum;
        printf("PI is approx %.50f\n", pi);
        printf("Time elapsed: %.6f seconds\n", t_end - t_start);
    }

    MPI_Finalize();
    return 0;
}