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Subject: Re: [OMPI users] possible bug exercised by mpi4py
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-05-24 11:22:05


On May 24, 2012, at 11:10 AM, Lisandro Dalcin wrote:

>> So I checked them all, and I found SCATTERV, GATHERV, and REDUCE_SCATTER all had the issue. Now fixed on the trunk, and will be in 1.6.1.
>
> Please be careful with REDUCE_SCATTER[_BLOCK] . My understanding of
> the MPI standard is that the the length of the recvcounts array is the
> local group size
> (http://www.mpi-forum.org/docs/mpi22-report/node113.htm#Node113)

I read that this morning and it made my head hurt.

I read it to be: reduce the data in the local group, scatter the results to the remote group.

As such, the reduce COUNT is sum(recvcounts), and is used for the reduction in the local group. Then use recvcounts to scatter it to the remote group.

...right?

-- 
Jeff Squyres
jsquyres_at_[hidden]
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