slide 30 of 37

Compute Pi Using MPI

#include 
#include 
#include 

main(int argc,
char **argv)
{
  register double width;
  double sum, lsum;
  register int intervals, i; 
  int nproc, iproc;

  /* Initialize MPI */
  if (MPI_Init(&argc, &argv) != MPI_SUCCESS) exit(1);
  MPI_Comm_size( MPI_COMM_WORLD, &nproc );
  MPI_Comm_rank( MPI_COMM_WORLD, &iproc );

  /* get the number of intervals */
  intervals = atoi(argv[1]);
  width = 1.0 / intervals;

  /* do the local computations */
  lsum = 0;
  for (i=iproc; i<intervals; i+=nproc) {
    register double x = (i + 0.5) * width;
    lsum += 4.0 / (1.0 + x * x);
  }

  /* sum across the local results & scale by width */
  lsum *= width;
  MPI_Reduce(&lsum, &sum, 1, MPI_DOUBLE,
             MPI_SUM, 0, MPI_COMM_WORLD);

  /* have only the console PE print the result */
  if (iproc == 0) {
    printf("Estimation of pi is %14.12lf\n", sum);
  }

  /* check-out */
  MPI_Finalize();
  exit(0);
}