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Subject: Re: [OMPI users] Broadcast and root process
From: George Bosilca (bosilca_at_[hidden])
Date: 2013-04-29 11:49:27


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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