/* 
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 <stdlib.h>
#include <mpi.h>

int main(int argc, char **argv)
{ 
  int i, my_id, num_proc, size, position;
  double *vec = NULL;
  char buf[1000];
  MPI_Status status;

  // 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)
  { // setup vec
    size = 12;
    vec = (double *)malloc(size * sizeof(double));

    for (i = 0; i < size; i++)
      vec[i] = 0.5 * i;

    // setup buf - first put the size and then put the vec
    position = 0;
    MPI_Pack(&size, 1, MPI_INT, buf, 1000, &position, MPI_COMM_WORLD);
    printf("position after int: %d\n", position);
    MPI_Pack(vec, size, MPI_DOUBLE, buf, 1000, &position, MPI_COMM_WORLD);
    printf("position after adding %d doubles: %d\n", size, position);

    // send the data
    MPI_Send(buf, position, MPI_PACKED, 1, 0, MPI_COMM_WORLD);
  }
  else if (my_id == 1)
  { // recv the data
    MPI_Recv(buf, 1000, MPI_PACKED, 0, 0, MPI_COMM_WORLD, &status);

    // find the size
    position = 0;
    MPI_Unpack(buf, 1000, &position, &size, 1, MPI_INT, MPI_COMM_WORLD);
    // setup vec
    vec = (double *)malloc(size * sizeof(double));
    MPI_Unpack(buf, 1000, &position, vec, size, MPI_DOUBLE, MPI_COMM_WORLD);

    printf("\nsize: %d vec[0]: %f, ..., vec[%d]: %f\n\n", size, vec[0], size - 1, vec[size - 1]);
  }

  // clear memory
  free(vec);

  // finalize MPI
  MPI_Finalize();

  return 0;
}