Sorry, I should have been more precise in my answer. Topology information is only used during neighborhood communications via the specialized API, in all other cases the communicator would behave as a normal, fully connected, communicator.
George. On Tue, Feb 15, 2022 at 9:28 AM Neil Carlson via users < users@lists.open-mpi.org> wrote: > > > 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? >
