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
