[petsc-dev] who broke petsc-dev

[Matthew Knepley]

On Sun, Nov 13, 2011 at 11:13 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Nov 13, 2011, at 5:05 PM, Matthew Knepley wrote:
>
> > On Sun, Nov 13, 2011 at 10:52 PM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> >
> >   The simplest fix is to only do this null space business if Amat exists.
> >
> > I did this.
> >
> >   But keep in mind that KSP and SNES now have two modes of operation,
> the second uses the DM to provide many of the items they need at setup
> time. This is different then the classic KSP and SNES where the only way to
> do things were with KSPSetOperators() and SNESSetFunction/Jacobian. This is
> why Jed is indicating that it may be too soon at this stage to muck with
> the null space business.
> >
> > This is bad. Things are becoming unacceptably complicated. I can't trust
> that obvious arguments are in this function,
> > and I can't trust that setup will be called since the logic is
> convoluted. This needs to be rethought.
>
>   Do you want to go back to the uncomposible DMMG?    The logic is not all
> that convoluted. Basically at setup time for any thing that has not be
> previously provided KSP and SNES try to use DM to provide them.
>

No. The setup logic for KSP is convoluted.


>  The alternative is to remove KSPSetOperators() and
> SNESSetFunction/Jacobian() and ONLY have them provided with DM.  I dislike
> this because it breaks our 15 year old model and all users (even the least
> skilled) need to deal with yet another object before they can solve the
> simplest thing. But I am open to other alternative designs that you might
> suggest.


I do not want that. I would rather that people using DM do not call
KSPSetOperators() at all. The only reason that we would call it
is to pass the preconditioner. I think this overloading of the interface
complicates things. I would prefer adding a call for the
preconditioning matrix, that gets called from KSPSetOeprators() and can be
called if you are using DM.

   Matt


>
>   Barry
>
> >
> >    Matt
> >
> >
> >   Barry
> >
> >
> > On Nov 13, 2011, at 4:47 PM, Matthew Knepley wrote:
> >
> > > On Sun, Nov 13, 2011 at 10:47 PM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> > >
> > > On Nov 13, 2011, at 4:45 PM, Matthew Knepley wrote:
> > >
> > > > On Sun, Nov 13, 2011 at 10:44 PM, Jed Brown <jedbrown at mcs.anl.gov>
> wrote:
> > > > On Sun, Nov 13, 2011 at 16:36, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> > > > 1) It is legitimate to call KSPSetOperators with a null Amat so this
> is a bug that crashes large parts of PETSc
> > > >
> > > > This logic should be moved much later (like to KSPSetUp()).
> > > >
> > > > I disagree, since SetOperators() is where we know that the matrix is
> changing.
> > >
> > >  Yes, but the matrix may not exist.
> > >
> > > I have no problem fixing this, but what does that mean? I can't fix it
> until I understand what you are doing here.
> > >
> > >   Matt
> > >
> > > >
> > > >    Matt
> > > >
> > > >
> > > >
> > > > 2) Do you really want to do this? I am not sure I like it.
> > > >
> > > > I think that attaching the null space to the Mat should be the
> preferred way to communicate it, especially in the case of a deeply nested
> hierarchy.
> > > >
> > > >
> > > >
> > > > --
> > > > 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
> > >
> > >
> > >
> > >
> > > --
> > > 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
> >
> >
> >
> >
> > --
> > 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
>
>


-- 
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
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