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Subject: Re: [OMPI users] Broadcast and root process
From: giggzounet (giggzounet_at_[hidden])
Date: 2013-04-30 03:52:06

ok. Thx for your answer. The documentation was not clear on this subject.


Le 29/04/2013 17:49, George Bosilca a écrit :
> No, the root processor can be different for every broadcast, but for a same broadcast every process involved must know who the root is. That's the only condition MPI imposes.
> George.
> On Apr 29, 2013, at 13:15 , giggzounet <giggzounet_at_[hidden]> wrote:
>> Hi,
>> I'm new on this list. I'm using MPI for years but I don't have written a
>> lot of code with MPI. Therefore is my question perhaps ridiculous:
>> I'm using a Computational Fluid Mechanics (CFD) Solver. This Solver uses
>> MPI to exchange the data between the different partitions. In this
>> solver the "root processor" is always the processor 1. So this proc
>> reads the input, broadcast a lot of things and writes the output.
>> During a time step the solver computes the reference pressure at a
>> point. This computation is done on a processor, which may not be the
>> root processor. Therefore after the computation a broadcast of the value
>> is necessary. For the moment in the code the broadcast is done with the
>> processor, where the reference pressure is computed, as root processor
>> (and not with the standard "root processor").
>> Is it false ? Must the root processor be the same during a computation
>> for all broadcasts ?
>> Best regards,
>> Guillaume
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