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From: Michael Kluskens (mkluskens_at_[hidden])
Date: 2006-03-27 10:49:22


Thank you. I was using MPI_ROOT in a MPI_Bcast call from the parent
process where I spawn subprocesses and it worked fine in OpenMPI but
when it didn't work on another platform and the support engineers
solution was to define it as zero I started looking and couldn't find
anything close to what you said below in the four books I have. Page
236 of Using MPI-2 shows the correct use of MPI_ROOT but no
explanation of why.


On Mar 27, 2006, at 10:21 AM, Edgar Gabriel wrote:

> MPI_ROOT is required for the rooted operations of the inter-
> communicator
> collectives in MPI-2, I am not aware of that you need MPI_ROOT in
> intra-communicator collectives as defined in MPI-1.
> Thanks
> Edgar
> Michael Kluskens wrote:
>> The constant MPI_ROOT is not universally defined in all current
>> shipping MPI implementations.
>> Is there any MPI function/call that requires MPI_ROOT?
>> From the complete reference it appears that MPI_ALLGATHER might be
>> the one routine.
>> This all relates to portability, code I write using OpenMPI has to
>> work on other systems not using OpenMPI.
>> Michael
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