We are primarily interested in MPICH2, as the motivation for this question relates to a particular supercomputer that uses MPICH2 and, in particular, the MPICH2 implementation of MPI_Reduce for (comm,type,op) of interest to us. Jeff On Mon, Nov 12, 2012 at 9:35 PM, Pavan Balaji <[email protected]> wrote:
The MPI standard does not guarantee this. For example, an implementation could use topology-aware reductions or an MPI_ANY_SOURCE while waiting for messages from peers making the order in which the reduction operations are applied different for each run.
-- Pavan
On 11/12/2012 09:00 PM US Central Time, Nichols A. Romero wrote:
Hi,
I apologize if this has been asked a trillion times, if its documented somewhere just point it out to me online.
Are collective operations, such as sums, using MPI_Reduce deterministic? In other words, if I run MPI_Reduce N times on P tasks, will the sums always occur in the same order. Thus it would be reproducible to the expected precision.
-- Pavan Balaji http://www.mcs.anl.gov/~balaji _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss
-- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute [email protected] / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond