#include <iostream>
#include <mpi.h>

using namespace std;

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

     MPI_Init(&argc, &argv);

     // Get the rank and size in the original communicator
     int worldRank, 
         worldSize;

     MPI_Comm_rank(MPI_COMM_WORLD, &worldRank);
     MPI_Comm_size(MPI_COMM_WORLD, &worldSize);

     int color = worldRank / 4; // Determine color based on row

     // Split the communicator based on the color and use the
     // original rank for ordering
     
     MPI_Comm rowComm;
     MPI_Comm_split(MPI_COMM_WORLD, color, worldRank, &rowComm);

     int rowRank, rowSize;
     MPI_Comm_rank(rowComm, &rowRank);
     MPI_Comm_size(rowComm, &rowSize);

     cout << "World Rank/size " << worldRank << "/" << worldSize;
     cout << " Row Rank/size " << rowRank << "/" << rowSize << endl;

     MPI_Comm_free(&rowComm);

     MPI_Finalize();

     return 0;
}