/* create datatype for one column */
MPI_Type_vector(NROWS, 1, NCOLS, MPI_INT, &column);
/* create datatype for one column, with the extent of one
/* create datatype for one column */
MPI_Type_vector(NROWS, 1, NCOLS, MPI_INT, &column);
/* create datatype for one column, with the extent of one