[Carpet] Which mpi communicator?

[Erik Schnetter]

On Sep 10, 2007, at 16:37:20, Yosef Zlochower wrote:

> Hi,
>
>   I have  routines scheduled in global mode that use mpi collective  
> calls.
> Which communicator should I use, *GetMPICommUniverse(cctkGH),
> or *GetMPICommWorld(cctkGH)? Are they the same when there is only
> 1 model used? Can these communicators change during the evolution?

You are, unless you surprise me very much, using a universe  
consisting of a single world.  For the future you should use the  
world communicator.  A universe can consist of several worlds, or  
could set e.g. I/O processors aside.  At the moment both are  
identical, and they do not change during evolution.  There are ideas  
to extend/reduce/replace processors at run time, e.g. if processors  
fail or if the simulation needs more storage, but nothing has been  
implement along these lines.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>

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