On Mon, Feb 14, 2022 at 9:01 PM George Bosilca <bosi...@icl.utk.edu> wrote:
> On Mon, Feb 14, 2022 at 6:33 PM Neil Carlson via users < > users@lists.open-mpi.org> wrote: > >> 1. Where can I use this communicator? Can it be used with the usual >> stuff like MPI_Allgather, or do I need to hang onto the original >> communicator (MPI_COMM_WORLD actually) for that purpose? >> > > Anywhere a communicator is used. You just have to be careful and > understand what is the scope of the communication you use them with. > Ah! I was thinking that this graph topology information might only be relevant to MPI_Neighbor collectives. But would it be proper then to think of a communicator having an implicit totally-connected graph topology that is replaced by this one? If so would Bcast, for example, only send from the root rank to those it was a source for in the graph topology? Or Gather on a rank only receive values from those ranks that were a source for it? What would the difference be then between Alltoallv, say, and Neighbor_alltoallv?
