/* 
Jonathan Hauenstein - University of Notre Dame
Center for Applied Mathematics Minicourse on Parallel Computing
April 24, May 1, May 8, 2008
Sample programs are designed for educational use 
*/

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

// computes the value of pi using a monte carlo integration

int samples_in_circle(int num_samples);

int main(int argc, char **argv)
{ 
  int my_id, num_proc, num_points = 0, my_points, my_count, total;

  // initialize MPI
  MPI_Init(&argc, &argv);

  // find unique id
  MPI_Comm_rank(MPI_COMM_WORLD, &my_id);

  // find the number of processes running
  MPI_Comm_size(MPI_COMM_WORLD, &num_proc);

  if (my_id == 0)
  { // find the number of sample points that the user wants to use
    int points_per_proc = 0;

    printf("Please enter the number of sample points to use: ");
    scanf("%d", &num_points);

    // quick error checking
    if (num_points <= 0)
    { 
      printf("The number of points was not read in properly.  This program will terminate!\n\n");
      MPI_Abort(MPI_COMM_WORLD, 1);
    }

    // split up the points equally between the other processors
    points_per_proc = num_points / num_proc;

    // find the number of points left over that will be computed on id 0
    my_points = num_points - points_per_proc * (num_proc - 1);

    // tell everyone else how many points they need to use
    MPI_Bcast(&points_per_proc, 1, MPI_INT, 0, MPI_COMM_WORLD);
  }
  else
  { // recv the number of points it will need to use
    MPI_Bcast(&my_points, 1, MPI_INT, 0, MPI_COMM_WORLD);
  }

  // on each process, do the monte carlo integration based on the number of points that it has 
  my_count = samples_in_circle(my_points);

  // collect the sum of the points in the circle on id 0
  MPI_Reduce(&my_count, &total, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);

  if (my_id == 0)
  { // compute the approximation of pi
    double pi = (4.0 * total) / num_points;
    printf("\nUsing %d points, the approximation to pi is %.15f.\n\n", num_points, pi);
  }

  // finalize MPI
  MPI_Finalize();

  return 0;
}