[R-sig-hpc] unusual results with Rmpi

Brian G. Peterson brian at braverock.com
Thu Dec 9 21:17:35 CET 2010

On 12/09/2010 10:33 AM, Maas James Dr (MED) wrote:
> I'm running a small programme as a test and to learn how to use Rmpi.
> I send a data set and routine to two slave nodes, and then get the answers back in an object.  The routines executed are Bayesian Gibbs sampling routines so I would expect slightly different answers back from the two nodes but I get identical answers back from both nodes.
> I'm under the impression that each node does the complete routine from start to finish before returning answers but this may be my misunderstanding.  Should the answers in fact be identical because mpi has split the job up between the two nodes and both contributed to the calculations, therefore both end up with the same answer?

See presentations by Dirk Eddelbuettel, Bryan Lewis, and others talking 
about initializing parallel random number streams in parallelized R 
sessions.  Alternately, you can set a different seed on each node.


   - Brian

Brian G. Peterson
Ph: 773-459-4973
IM: bgpbraverock

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