[mpich-discuss] determinism in collectives

[Pavan Balaji]

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