#include <stdlib.h>#include <stdio.h>#include <math.h>#include <mpi.h>int main(int argc, char **argv){  int i, val1, val2;  int rank, size, dir;  int left, right, up, down;  const int ndim = 2, reorder = 1, disp = 1;  int dims[ndim], periods[ndim], coords[ndim];  MPI_Comm MPI_COMM_CART;  MPI_Init(&argc, &argv);  MPI_Comm_size(MPI_COMM_WORLD, &size);  for(i = 0; i < ndim; i++)  {    dims[i] = sqrt(size);    periods[i] = 1;  }  MPI_Cart_create(MPI_COMM_WORLD, ndim, dims, periods, reorder, &MPI_COMM_CART);  MPI_Comm_rank(MPI_COMM_CART, &rank);  MPI_Cart_coords(MPI_COMM_CART, rank, ndim, coords);  dir = 0;  MPI_Cart_shift(MPI_COMM_CART, dir, disp, &up, &down);  dir = 1;  MPI_Cart_shift(MPI_COMM_CART, dir, disp, &left, &right);  printf("Processor %d, has coords (%d, %d), and neighbors up %d, down %d, left %d, right %d\n",	 rank, coords[0], coords[1], up, down, left, right);  if(rank == 0)    printf("Sending to the right\n");  val1 = rank;  MPI_Sendrecv_replace(&val1, 1, MPI_INT, right, 0, left, 0, MPI_COMM_CART,		       MPI_STATUS_IGNORE);  if(rank == 0)	  printf("Sending down\n");  val2 = rank;  MPI_Sendrecv_replace(&val2, 1, MPI_INT, right, 0, left, 0, MPI_COMM_CART,		       MPI_STATUS_IGNORE);  MPI_Barrier(MPI_COMM_CART);  if(rank == 0)	  printf("Done\n");  MPI_Finalize();  return EXIT_SUCCESS;}