[Trilinos-Users] [EXTERNAL] MTSGS Smoother Behavior

[Duncan Karnitz]

Siva,

 We use Belos BiCGStab, with MueLu preconditioning using the MTSGS smoother as an inner
 loop linear solver. We have a particular problem we are running with four threads have
 significantly different behavior between repeated runs. (i.e. no two solves are the
 same). There are a lot of factors in play, but we believe we have isolated the issue
 to the Belos solver, or the preconditioner & smoother.

 I understand the generalized coloring approach in order to make SGS thread-safe, but
 I would expect between two identical runs of a problem that the coloring would be the
 same. Subsequently I would expect always running with the same number of threads to
 have consistent behavior.

-Duncan

----- Original Message -----
From: "Rajamanickam, Sivasankaran" <srajama at sandia.gov>
To: "dlk" <dlk at thermoanalytics.com>, "trilinos-users" <trilinos-users at trilinos.org>
Sent: Wednesday, March 13, 2019 5:00:05 PM
Subject: Re: [EXTERNAL] [Trilinos-Users] MTSGS Smoother Behavior

Duncan
  MT-SGS uses coloring and multithreading using the coloring. Slight variations in #iterations are expected when used stand-alone. What is the behavior you are seeing ?

Thanks
Siva

________________________________________
From: Trilinos-Users <trilinos-users-bounces at trilinos.org> on behalf of Duncan Karnitz <dlk at thermoanalytics.com>
Sent: Wednesday, March 13, 2019 2:06 PM
To: trilinos-users
Subject: [EXTERNAL] [Trilinos-Users] MTSGS Smoother Behavior

I am investigating some inconsistent multi-threaded behavior when using
the MueLu MTSGS smoother. When using more than one thread, we see that
no two runs of our solve code produce the same convergence behavior.

Is there anything in the MTSGS implementation that might not reproduce
the same computations each time when using more than one thread?

Thank you,
Duncan Karnitz
_______________________________________________
Trilinos-Users mailing list
Trilinos-Users at trilinos.org
https://trilinos.org/mailman/listinfo/trilinos-users