pi.c

/*

This program will numerically compute the integral of

                  4/(1+x*x)

from 0 to 1.  The value of this integral is pi -- which
is great since it gives us an easy way to check the answer.

The is the original sequential program.  It uses the timer
from the OpenMP runtime library

History: Written by Tim Mattson, 11/99.

*/
#include <omp.h>
#include <stdio.h>
static long num_steps = 100000000;
double step;
int main() {
  int i;
  double x, pi, sum = 0.0;
  double start_time, run_time;

  step = 1.0 / (double)num_steps;

  start_time = omp_get_wtime();

  for (i = 1; i <= num_steps; i++) {
    x = (i - 0.5) * step;
    sum = sum + 4.0 / (1.0 + x * x);
  }

  pi = step * sum;
  run_time = omp_get_wtime() - start_time;
  printf("\n pi with %ld steps is %lf in %lf seconds\n ", num_steps, pi,
         run_time);
}