[petsc-dev] Bug introduced in MatGetSubmatrices()

[Matthew Knepley]

On Fri, Jan 20, 2017 at 11:55 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On Jan 20, 2017, at 11:49 AM, Matthew Knepley <knepley at gmail.com> wrote:
> >
> > On Fri, Jan 20, 2017 at 10:49 AM, Hong <hzhang at mcs.anl.gov> wrote:
> > Matt,
> > By default, the flag C->submat_singleis = false.
> > In PCSetUp_ASM(), we set it as 'true' to use MatGetSubMatrices_MPIAIJ_
> SingleIS().
> >
> > Can you check the value of this flag in your case?
> >
> > The problem is the following:
> >
> >   1) We use MatGetSubMatrices() to extract small matrices in order to
> form a preconditioner
> >
> >   2) We do this at each Newton iteration
> >
> >   3) We use ASM as a preconditioner for the eventual Newton solve
> >
> >   4) The second time we call MatGetSubMatrices(), it has this flag set,
> even though we are using multiple ISes
> >
> > Solution: ALSO check that the user is in fact passing a single IS.
> >
>     This requires a communication. I am confused, is the number of IS
> changing each time? If not why is the flag set?


ASM sets this flag because it knows that IT is going to call
MatGetSubMatrices() later, but it unsafe if any user calls
MatGetSubMatrices() as well. I think overall its a fragile design and
should be scrapped.

  Matt


>
>    Barry
>
> >   Matt
> >
> > Hong
> >
> > It comes from here:
> >
> >   https://bitbucket.org/petsc/petsc/commits/
> c10200c1442b553b7ad65c70101560db4fa22e78
> >
> > If we ask for more than 1 matrix, it dispatches to
> >
> >   MatGetSubMatrices_MPIAIJ_SingleIS()
> >
> > but then fails here
> >
> >   https://bitbucket.org/petsc/petsc/annotate/
> 2e559809f9aee9c95ee79eb0939630cfe5502c8d/src/mat/impls/aij/
> mpi/mpiov.c?at=master&fileviewer=file-view-default#mpiov.c-1306
> >
> > because ismax > 1. I think the ismax check needs to move up to here
> >
> >   https://bitbucket.org/petsc/petsc/annotate/
> 2e559809f9aee9c95ee79eb0939630cfe5502c8d/src/mat/impls/aij/
> mpi/mpiov.c?at=master&fileviewer=file-view-default#mpiov.c-2012
> >
> > but I don't know for sure. Please fix this since it is breaking PyLith.
> >
> >   Matt
> >
> > --
> > 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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