Hi all,
I'm getting increasingly concerned about SELL not being a subclass of
AIJ. As such, we have to deal with all these fallback operations now,
whereas as a subclass of AIJ we could just selectively make use of the
SELL format where we really benefit from it. "Use AIJ by default unless
we have something optimized for SELL" is just much more appropriate for
the few use cases of SELL than the current "SELL has to implement
everything and usually this means to manually convert back to AIJ".
If there are no objections I'd like to clean this up. (Subclassing AIJ
was unfortunately not available at the time Hong started his great work
on SELL)
Best regards,
Karli
On 03/03/2018 07:52 AM, Richard Tran Mills wrote:
Resurrecting a few weeks old thread:
Stefano, did you get around to coding something up to do an automatic
conversion to SeqAIJ for operations unsupported by SELL format? I did
some hacking the other day to try to get PCGAMG to use SELL inside the
smoothers and this turns out to be way more complicated than I'd like
and very bug prone (I haven't found all of mine, anyway). I think it may
be preferable to be able to pass a SELL matrix to PCGAMG and have an
internal conversion happen in the SELL matrix to AIJ format for doing
the MatPtAP and LU solves. Support for this would certainly make it
easier for users in a lot other cases as well, and might make the use of
SELL much more likely. If no one has already done some work on this,
I'll take a stab at it.
--Richard
On Mon, Feb 12, 2018 at 10:04 AM, Richard Tran Mills <rtmi...@anl.gov
<mailto:rtmi...@anl.gov>> wrote:
On Mon, Feb 12, 2018 at 8:47 AM, Smith, Barry F. <bsm...@mcs.anl.gov
<mailto:bsm...@mcs.anl.gov>> wrote:
> On Feb 12, 2018, at 10:25 AM, Stefano Zampini <stefano.zamp...@gmail.com
<mailto:stefano.zamp...@gmail.com>> wrote:
>
> Barry,
>
> for sure Amat,Pmat is the right approach; however, with complicated
user codes, we are not always in control of having a different Jacobian matrix.
> Since Mat*SELL does not currently support any preconditioning except
PCSOR and PCJACOBI, we ask the user to put codes like
>
> if (type is SELL)
> create two matrices (and maybe modify the code in many other parts)
> else
> ok with the previous code
I don't disagree with what you are saying and am not opposed
to the proposed work.
Perhaps we need to do a better job with making the mat,pmat
approach simpler or better documented so more people use it
naturally in their applications.
I wrote some code like that in some of the Jacobian/function
routines in PFLOTRAN to experiment with MATSELL, and it works, but
looks and feels pretty hacky. And if I wanted to support it for all
of the different systems that PFLOTRAN can model, then I'd have to
reproduce that it in many different Jacobian and function evaluation
routines. I also don't like that it makes it awkward to play with
the many combinations of matrix types and preconditioners that PETSc
allows: The above pseudocode should really say "if (type is SELL)
and (preconditioner is not PCSOR or PCJACOBI)". I do think that
Amat,Pmat is a good approach in many situations, but it's easy to
construct scenarios in which it falls short.
In some situations, what I'd like to have happen is what Stefano is
talking about, with an automatic conversion to AIJ happening if SELL
doesn't support an operation. But, ideally, I think this sort of
implicit format conversion shouldn't be something hard-coded into
the workings of SELL. Instead, there should be some general
mechanism by which PETSc recognizes that a particular operation is
unsupported for a given matrix format, and then it can (optionally)
copy/convert to a different matrix type (probably default to AIJ,
but it shouldn't have to be AIJ) that supports the operation. This
sort of implicit data rearrangement game may actually become more
important if future computer architectures strongly prefer different
data layouts different types of operations (though let's not get
ahead of ourselves).
--Richard
Barry
>
> Just my two cents.
>
>
> 2018-02-12 19:10 GMT+03:00 Smith, Barry F.
<bsm...@mcs.anl.gov <mailto:bsm...@mcs.anl.gov>>:
>
>
> > On Feb 12, 2018, at 9:59 AM, Stefano Zampini
<stefano.zamp...@gmail.com <mailto:stefano.zamp...@gmail.com>>
wrote:
> >
> > FYI, I just checked and MatSOR_*SELL does not use any
vectorized instruction.
> > Why just not converting to SeqAIJ, factor and then use the
AIJ implementation for MatSolve for the moment?
>
> Why not use the mat, pmat feature of the solvers to pass in
both matrices and have the solvers handle using two formats
simultaneously instead of burdening the MatSELL code with tons
of special code for automatically converting to AIJ for solvers etc?
>
>
> >
> > 2018-02-12 18:06 GMT+03:00 Stefano Zampini
<stefano.zamp...@gmail.com <mailto:stefano.zamp...@gmail.com>>:
> >
> >
> > 2018-02-12 17:36 GMT+03:00 Jed Brown <j...@jedbrown.org
<mailto:j...@jedbrown.org>>:
> > Karl Rupp <r...@iue.tuwien.ac.at
<mailto:r...@iue.tuwien.ac.at>> writes:
> >
> > > Hi Stefano,
> > >
> > >> Is there any plan to write code for native ILU/ICC etc
for SeqSELL, at least to have BJACOBI in parallel?
> > >
> > > (imho) ILU/ICC is a pain to do with SeqSELL. Point-Jacobi
should be
> > > possible, yes. SELL is really just tailored to MatMults
and a pain for
> > > anything that is not very similar to a MatMult...
> >
> > There is already MatSOR_*SELL. MatSolve_SeqSELL wouldn't
be any harder.
> > I think it would be acceptable to convert to SeqAIJ,
factor, and convert
> > the factors back to SELL.
> >
> > Yes, this was my idea. Today I have started coding
something. I'll push the branch whenever I have anything working
> >
> >
> >
> > --
> > Stefano
> >
> >
> >
> > --
> > Stefano
>
>
>
>
> --
> Stefano
