[petsc-users] [MEF-QUAR] Re: Any changes in ML usage between 3.1-p8 -> 3.3-p6?

[Matthew Knepley]

On Wed, Apr 17, 2013 at 12:26 PM, Jozsef Bakosi <jbakosi at lanl.gov> wrote:

> On 04.05.2013 08:34, Jozsef Bakosi wrote:
> > Hi folks,
> >
> > In switching from 3.1-p8 to 3.3-p6, keeping the same ML ml-6.2.tar.gz, I
> get
> > indefinite preconditioner with the newer PETSc version. Has there been
> anything
> > substantial changed around how PCs are handled, e.g. in the defaults?
> >
> > I know this request is pretty general, I would just like to know where
> to start
> > looking, where changes in PETSc might be clobbering the (supposedly same)
> > behavior of ML.
> >
>
> Alright, here is a little more information about what we see. Running the
> same
> setup/solve using ML (using the same ML and application source code) and
> switching from PETSc 3.1-p8 to 3.3-p6 appears to work differently, in some
> cases, resulting in divergence compared to the old version.
>
> I attach the output from KSPView() called after KSPSetup() for the 3.1-p8
> (old.out) and for the 3.3-p6 (new.out), both running on 4 MPI ranks.
>
> A diff reveals some notable differences:
>
>   * using (PRECONDITIONED -> NONE) norm type for convergence test
>
>   * (using -> not using) I-node routines
>
>   * tolerance for zero pivot (1e-12 -> 2.22045e-14) for
> PPE_mg_levels_[12]_sub_
>     (stayed the same for PPE_mg_coarse_redundant_)
>
> So we are wondering what might have changed in the PETSc defaults around
> how
> PCs, in particular ML, is used.
>
> Thanks, and please let me know if I can give you more information,
>

1) Please do not give error reports without the full error message

2) If you get "Indefinite PC" (I am guessing from using CG) it is because
the preconditioner
    really is indefinite (or possible non-symmetric). We improved the
checking for this in one
    of those releases.

AMG does not guarantee an SPD preconditioner so why persist in trying to
use CG?

    Matt


> Thanks,
> Jozsef
>



-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130417/057cbe6e/attachment.html>