Create Row Groups

int my_row, q, my_rank_in_row;

q = (int) sqrt((double) p);

/* my_rank is rank in MPI_COMM_WORLD, q*q = p */

my_row = my_rank/q;

MPI_Comm_split(MPI_COMM_WORLD, my_row, my_rank, &my_row_comm);

/* Test the new communicators */

MPI_Comm_rank(my_row_comm, &my_rank_in_row);

if (my_rank_in_row == 0)

test = my_row;

else

test = 0;

MPI_Bcast(&test, 1, MPI_INT, 0, my_row_comm);

printf("Process %d > my_row = %d, my_rank_in_row = %d, test = %d\n",

my_rank, my_row, my_rank_in_row, test);