pi-c.c

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/* File:       pi-c.c
 *
 * Purpose:    Estimates pi using the Leibniz formula (in C).
 *
 * NOTE: We use mpicc to compile here because we are using the MPI timing
 * function (MPI_Wtime).
 *
 * Compile:    mpicc -g -Wall -o pi-c pi-c.c
 * Run:        ./pi-c
 */

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

/* We define pi here so we can check and see how accurate our computation is. */
#define PI 3.141592653589793238462643

int main(int argc, char **argv) {
    int intervals;
    printf("Number of intervals: ");
    fflush(stdout);
    scanf("%d", &intervals);

    double time1 = MPI_Wtime();

    int i;
    double sum, total = 0;
    for (i = 0; i < intervals; ++i) {
        total += pow(-1, i) / (2 * i + 1);
    }

    double time2 = MPI_Wtime();

    total = total * 4;
    printf("Result:   %.10lf\n", total);
    printf("Accuracy: %.10lf\n", PI - total);
    printf("Time:     %.10lf\n", time2 - time1);
}