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Subject: Re: [OMPI users] send and receive buffer the same on root
From: David Zhang (solarbikedz_at_[hidden])
Date: 2010-09-16 12:58:47


It's compiler specific I think. I've done this with OpenMPI no problem,
however on one another cluster with ifort I've gotten error messages about
not using MPI_IN_PLACE. So I think if it compiles, it should work fine.

On Thu, Sep 16, 2010 at 10:01 AM, Tom Rosmond <rosmond_at_[hidden]> wrote:

> I am working with a Fortran 90 code with many MPI calls like this:
>
> call mpi_gatherv(x,nsize(rank+1),
> mpi_real,x,nsize,nstep,mpi_real,root,mpi_comm_world,mstat)
>
> 'x' is allocated on root to be large enough to hold the results of the
> gather, other arrays and parameters are defined correctly, and the code
> runs as it should. However, I am concerned that having the same send
> and receive buffer on root is a violation of the MPI standard. Am I
> correct? I am aware of the MPI_IN_PLACE feature that can be used in
> this situation, by defining it as the send buffer at root.
>
> The fact that the code as written seems to work on most system we run on
> (some with OpenMPI, some with proprietary MPI's) indicates that in spite
> of the standard, implementations allow it. Is this correct, or are we
> just lucky.
>
> T. Rosmond
>
>
>
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-- 
David Zhang
University of California, San Diego