[Trilinos-Users] Different results from AztecOO/ML when running serial vs parallel

[Eric Marttila]

Thanks Mike, that is good to know.
--Eric

On Friday, January 30, 2015 03:08:04 pm Heroux, Michael A wrote:
> Eric,
> 
> It is fairly common to see an increase in iteration count to
> reach the same residual value.  The quality of the
> preconditioner tends to decay as the number of processors
> increases.
> 
> Mike
> 
> 
> ________________________________________
> From: trilinos-users-bounces at software.sandia.gov
> <trilinos-users-bounces at software.sandia.gov> on behalf of
> Eric Marttila <eric.marttila at thermoanalytics.com> Sent:
> Friday, January 30, 2015 1:21 PM
> To: Trilinos-Users at software.sandia.gov
> Subject: [EXTERNAL] [Trilinos-Users] Different results from
> AztecOO/ML when running     serial vs parallel
> 
> I'm using AztecOO with ML to perform linear solves within a
> non- linear outer iteration loop.  Experimentation has shown
> that I get the best overall convergence (i.e. fastest
> solution) of my non-linear solve if use a small number of
> iterations in AztecOO when doing each linear solve.
> 
> The problem I have is that when running the code with
> different numbers of processes I see significantly different
> results from the linear solve.
> 
> I've attached a small code sample that exercises this issue by
> performing a single linear solve.  When running this code with
> np=1 and np=4, I see differences in results that are about
> 0.5%.
> 
> If I let AztecOO do more iterations, most of the differences
> go away... but this isn't what I want to do since it causes
> my total non-linear solution time to increase.
> 
> I was not expecting to see the 0.5% difference in results when
> running serial vs parallel.  I was expecting differences that
> are closer to machine precision (like I see when I have
> AztecOO iterate more).  Is what I'm seeing the expected
> behavior? Or am I perhaps doing something wrong in setting up
> AztecOO?
> 
> Thanks,
> --Eric
> 
> p.s. Attached is my source code, as well as a separate .tar.gz
> that contains the input files and sample output files.
> 
> --
> Eric A. Marttila

-- 
Eric A. Marttila
ThermoAnalytics, Inc.
Email: Eric.Marttila at ThermoAnalytics.com
Phone: 810-636-2443
http://www.thermoanalytics.com