[petsc-dev] why does MatCreate_MPIDense still exist?

[Hong Zhang]

Barry :

>
>    1) One problem is all the parallel MatMatSolve() use the MPIDense
> matrices.  What is the likelihood that they could be changed to use the
> elemental matrices (note that with the MPIDense matrices using the simple
> array format the MatMatSolve() codes are very straight ward and do not need
> crazy remappings.
>
>      2) The MPIDense matrices use MatGetArray() all over the place; which
> would not work with any non-trivial cyclic storage crap that those guys
> love. I may need to write a temporary MatMPIDenseGetArray() until the
> MPIDense business can be resolved.
>
>      Do we need to keep MPIDense around and just strip out all of it that
> uses plapack? If that is possible?
>
I prefer this approach, i.e., "just strip out all of it that uses plapack",
and keep MPIDense, which is useful as
petsc dense multi-vectors, and perhaps other usage.

Hong

>
>
>
>
> On Aug 13, 2012, at 12:14 PM, Matthew Knepley <knepley at gmail.com> wrote:
>
> > On Mon, Aug 13, 2012 at 12:07 PM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> >
> > On Aug 13, 2012, at 12:05 PM, Hong Zhang <hzhang at mcs.anl.gov> wrote:
> >
> > > Barry,
> > > Elemental interface is not well tested yet.
> > > I would wait for few months to remove PLAPACK stuff.
> >
> >     PLAPACK stuff is (and never was) well tested. Does anyone rely on
> it? I hope not. And I hate to have someone new come along and rely on it.
> >
> > I am for removing it. I wrote it, and so I can guarantee that it is not
> maintained. We should
> > just fix anything that comes up rather than fooling ourselves that this
> current stuff works.
> >
> >    Matt
> >
> >
> >     Barry
> >
> > >
> > > Hong
> > >
> > > On Mon, Aug 13, 2012 at 11:50 AM, Jed Brown <jedbrown at mcs.anl.gov>
> wrote:
> > > On Mon, Aug 13, 2012 at 10:40 AM, Barry Smith <bsmith at mcs.anl.gov>
> wrote:
> > > Should I remove all the MPIDense stuff from PETSc now?   It is uses
> PLAPACK which is buggy and unsupported.
> > >
> > > That is still a good distribution for MxN matrices with M>>N. We can
> do them with Elemental, but that would use a different distribution so it
> will be more complicated to interact with. (The current Elemental interface
> uses a squarish distribution, but we can tell Elemental to use the [VC,*]
> distribution (for which fewer operations are supported).
> > >
> > > The main thing I care about for that distribution is QR. The best
> format is dense and row-aligned. I don't care whether it uses MPIDense or a
> new "multi-vector" thing, but that concept should be somewhere.
> > >
> >
> >
> >
> >
> > --
> > 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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