[Users] bug in Dissipation thorn?

Frank Loeffler knarf at cct.lsu.edu
Fri Feb 22 11:24:11 CST 2013

On Fri, Feb 22, 2013 at 06:01:19PM +0100, Ian Hinder wrote:
> I disagree.  Reductions should be deterministic;

That would be nice, but in practice this is not the case.

> assuming the same number of MPI processes, the contributions to the
> reduction should always be added in the same order.

I agree that you should be able to do that, even efficiently.

However, reductions might locally be done faster with OpenMP, and there
you loose unless you are very careful to avoid undefined ordering. I
don't think Carpet does this, or how difficult that would actually be.


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