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Subject: Re: [OMPI users] "An error occurred in MPI_Recv" with more than 2 CPU
From: vasilis (gkanis_at_[hidden])
Date: 2009-05-28 03:30:06


On Wednesday 27 of May 2009 8:35:49 pm Eugene Loh wrote:
> George Bosilca wrote:
> > This is a problem of numerical stability, and there is no solution
> > for such a problem in MPI. Usually, preconditioning the input
> > matrix improve the numerical stability.
>
> At the level of this particular e-mail thread, the issue seems to me to
> be different. Results are added together in some arbitrary order and
> there are variations on order of 10^-10. This is not an issue of
> numerical stability, but just of bitwise floating-point reproducibility.
>
> And, given that one could fix the order (by using explicit source
> processes instead of MPI_ANY_SOURCE), one could "fix" this particular
> problem in MPI.
>
> Anyhow, I'm just picking nits here.

Eugene,

I really do not understand why you insist on the order. Maybe there is
something subtle about the order that I do not understand. Anyhow, I changed
the code according to your suggestion.

Thank you,
Vasilis