/*********************************************************************
       Example: Virtual topologies and communicators

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

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

  int myid,nproc,rank,i,j,subrank,data,mydata;
  MPI_Comm proc_grid, proc_row;
  int coords[2],pos[2],reorder=1,ndim=2,dims[2]={0,0},periods[2]={0,0};
  MPI_Status stat;



  // Initialize MPI 
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD,&nproc);




  // Create a virtual 2D-grid topology
  MPI_Dims_create(nproc,ndim,dims);
  MPI_Cart_create(MPI_COMM_WORLD,ndim,dims,periods,reorder,&proc_grid);
  MPI_Comm_rank(proc_grid,&myid);    // Note: use proc_grid




  // Create a communicator for each row
  MPI_Cart_coords(proc_grid,myid,ndim,coords); 
  MPI_Comm_split(proc_grid,coords[0],coords[1],&proc_row);
  MPI_Comm_rank(proc_row,&subrank); 




  // Broadcast within a row
  if (subrank==0)
    mydata=coords[0];
  MPI_Bcast(&mydata,1,MPI_INT,0,proc_row);



  // Check the result of Broadcast
  for (i=0; i<dims[0]; i++){
    for (j=0; j<dims[1]; j++){
      pos[0]=i; pos[1]=j;
      MPI_Cart_rank(proc_grid,pos,&rank);
	if (rank==myid)
	  printf("Rank: %d, Coords: %d %d, Data: %d\n", myid,i,j,mydata);
    }
  }



  // Exit and clean up MPI variables
  MPI_Comm_free(&proc_row);
  MPI_Comm_free(&proc_grid);
  MPI_Finalize();
}