Adrian Croucher <[email protected]> writes: > On 12/3/21 5:31 PM, Jed Brown wrote: >> You'd need more calls in case of overlap (so MPI_Comm_create_group is more >> natural), but non-participating ranks is easy. >> >> | A process may supply the color value MPI_UNDEFINED, in which case >> newcomm returns MPI_COMM_NULL. > > Ah, interesting. I guess mpi_comm_split() might also have the advantage > that each rank only needs to know if it is in the group or not, rather > than needing an array of all participating ranks, as mpi_comm_create() > and mpi_comm_create_group() do.
That's exactly why it's often more convenient. But it is collective on the parent communicator.
