Rick,
if you are using an inter communicator, please refer to the man page (a
group has to use MPI_ROOT as the root argument)
Cheers,
Gilles
On 10/21/2016 3:36 PM, George Bosilca wrote:
Rick,
There are few requirements to use any communicator in a collective
operation (including MPI_Reduce), and most of them are common sense.
All ranks in the communicator must call the collective, and the
different ranks should all reach the collective together (no unmatched
blocking communications should exists before the collective on some
ranks). To focus on the MPI_Reduce, all participants should also
provide the same root rank, which should be bounded by 0 and by the
communicator size, the same MPI_Op, and the same amount of data.
If I might I would suggest a good MPI-related book, "Using MPI ..." by
Gropp, Lusk and Skjellum (ISBN 978-0262527392). The examples are
freely available online at
http://www.mcs.anl.gov/research/projects/mpi/usingmpi/.
George.
On Wed, Oct 19, 2016 at 5:50 PM, Marlborough, Rick
<rmarlboro...@aaccorp.com <mailto:rmarlboro...@aaccorp.com>> wrote:
Designation: Non-Export Controlled Content
Folks;
My MPI_COMM_WORLD size is 2000. I have created a
communicator based on a small subset. I have used this
communicator in MPI_Barrier calls and it seems to work fine. Now I
want to use this in MPI_Reduce. When I do this I get errors like
“invalid root” or more mysteriously “on communicator MPI
communicator 7 group from 0… invalid argument of some kind.”. can
someone specify how to use a communicator (that is not COMM_WORLD)
with MPI_Reduce and specify rank properly.
Thanx
Rick
_3.1.1001
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