[petsc-users] mixed precision

[Jim Fonseca]

Okay, thank you for the guidance.
Jim


On Mon, Aug 12, 2013 at 1:38 PM, Karl Rupp <rupp at mcs.anl.gov> wrote:

> Hi Jim,
>
> in addition to what Matt already said, keep in mind is that you usually
> won't see a two-fold performance gain in iterative solvers anyway, as the
> various integers used for storing the nonzeros in the sparse matrix don't
> change their size. I once played with an implementation of an
> non-preconditioned mixed-precision CG solver, and I only obtained about a
> 40 percent overall performance gain for well-conditioned systems. For less
> well-conditioned systems you may not get any better overall performance at
> all (or worse, fail to converge).
>
> Best regards,
> Karli
>
>
>
> On 08/12/2013 12:32 PM, Matthew Knepley wrote:
>
>> On Mon, Aug 12, 2013 at 12:24 PM, Jim Fonseca <jefonseca at gmail.com
>> <mailto:jefonseca at gmail.com>> wrote:
>>
>>     Hi,
>>     We are curious about the mixed-precision capabilities in NEMO5. I
>>     see that there is a newish configure option to allow single
>>     precision for linear solve. Other than that, I found this old post:
>>     https://lists.mcs.anl.gov/**mailman/htdig/petsc-users/**
>> 2012-August/014842.html<https://lists.mcs.anl.gov/mailman/htdig/petsc-users/2012-August/014842.html>
>>
>>     Is there any other information about to see if we can take advantage
>>     of this capability?
>>
>>
>> Mixed-precision is hard, and especially hard in PETSc because the C type
>> system is limited.
>> However, it also needs to be embedded in an algorithm that can take
>> advantage of it. I would
>> always start out with a clear motivation:
>>
>>    - What would mixed precision accomplish in your code?
>>
>>    - What is the most possible benefit you would see?
>>
>> and decide if that is worth a large time investment.
>>
>>     Thanks,
>>     Jim
>>
>>     --
>>     Jim Fonseca, PhD
>>     Research Scientist
>>     Network for Computational Nanotechnology
>>     Purdue University
>>     765-496-6495 <tel:765-496-6495>
>>     www.jimfonseca.com <http://www.jimfonseca.com>
>>
>>
>>
>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which
>> their experiments lead.
>> -- Norbert Wiener
>>
>
>


-- 
Jim Fonseca, PhD
Research Scientist
Network for Computational Nanotechnology
Purdue University
765-496-6495
www.jimfonseca.com
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