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

int main(int argc, char *argv[])
{

  int world_rank, row_rank, col_rank, cart_rank;
  int nprocs, row_size, col_size;
  int coords[2], sub_coords[2];
  int dims[2] = { 0, 0}, period[2] = { 1, 1};
  int src_rank, dst_rank;
  int sum, temp;
  float avg;

  MPI_Comm cart_grid, cart_row, cart_col;
  MPI_Status status;

  /* MPI Initialization */
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
  MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);

  /* Cartesian grid creation */
  ... call MPI_Dims_create to get grid dimensions
  ... call MPI_Cart_create to create new topology

  /*Local world_rank initialization and comparison to global world_rank */
  ... call MPI_Comm_rank to get cartesian rank

  printf ("I am world_rank %d in MPI_COMM_WORLD and world_rank %d in the cartesian communicator\n",
      world_rank, cart_rank);

  /* Coordinates creation and neighbour communication */
  ... call MPI_Cart_coords to get process coordinates

  /* Communication south */
  sum = world_rank;
  ... call MPI_Cart_shift to prepare south-ward communication
  ... call MPI_Sendrecv to send world_rank and get temp from neighbour
  sum += temp;

  /* Communication north */
  ... call MPI_Cart_shift to prepare north-ward communication
  ... call MPI_Sendrecv to send world_rank and get temp from neighbour
  sum += temp;

  /*Communication east */
  ... call MPI_Cart_shift to prepare east-ward communication
  ... call MPI_Sendrecv to send world_rank and get temp from neighbour
  sum += temp;

  /*Communication west */
  ... call MPI_Cart_shift to prepare west-ward communication
  ... call MPI_Sendrecv to send world_rank and get temp from neighbour
  sum += temp;

  /*Neighbour's average */
  avg = (float) sum / 5;
  printf("Cart rank %d (%d, %d), neighbours average: %.2f\n", cart_rank, coords[0], coords[1], avg);

  /*Row sub-communicator creation */
  sum = 0;
  ... call MPI_Cart_sub to create row sub-spaces
  ... call MPI_Comm_size and MPI_Comm_rank to get size and rank in sub-space

  /*Row sub-communicator's average calculation */
  ... call MPI_Reduce to sum-up world ranks in sub-space

  if (row_rank == 0) {
    avg = (float) sum / row_size;
    printf("Row %d, row average: %.2f\n", coords[0], avg);
  }

  /*Column sub-communicator creation */
  sum = 0;
  ... call MPI_Cart_sub to create column sub-spaces
  ... call MPI_Comm_size and MPI_Comm_rank to get size and rank in sub-space

  /*Column sub-communicator's average calculation */
  ... call MPI_Reduce to sum-up world ranks in sub-space

  if (col_rank == 0) {
    avg = (float) sum / col_size;
    printf("Column %d, column average: %.2f\n", coords[1], avg);
  }

  /* Finalization operations */
  MPI_Comm_free(&cart_grid);
  MPI_Comm_free(&cart_col);
  MPI_Comm_free(&cart_row);
  MPI_Finalize();

  return 0;
}