/* ===========================================================
   compute Pi by integrating the function 1/SQRT(1-x^2)
   =========================================================== */

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

double f(double a)
{
   return( 2.0 / sqrt(1 - a*a) );
}

/* =======================
   MAIN
   ======================= */

int main(int argc, char *argv[])
{
   int    i;
   int    N;
   double pi;
   double w, x;

   /* -----
      Check command line
      ----- */
   if ( argc != 2 )
   {
      printf("Usage: %s  Num_Intervals\n", argv[0]);
      exit(1);
   }

   /* -----
      Get number of intervals and number of threads
      ----- */
   N = atoi(argv[1]);
   w = 1.0/(double) N;

   pi = 0.0;

   for (i = 0; i < N; i = i + 1)
   {
      x = (i + 0.5)*w;
      pi = pi +  w*f(x);
   }

   printf("Computed Pi = %lf\n\n", pi);

}