That clears up my uncertainty then. Thanks! On Tue, Feb 15, 2022 at 9:03 AM George Bosilca <bosi...@icl.utk.edu> wrote:
> 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? >> >
