[petsc-users] Valgrind Errors

[James Balasalle]

Hi Barry,

Thanks for the response.  You're right, it (both ex70 and my own code) doesn't give those valgrind errors when I run it in parallel.  Changing the type to MATAIJ also fixes the issue.

Thanks for the help, I appreciate it.

    James





> -----Original Message-----
> From: Hong [mailto:hzhang at mcs.anl.gov]
> Sent: Friday, September 12, 2014 4:29 PM
> To: Dominic Meiser
> Cc: Barry Smith; James Balasalle; Zhang, Hong; petsc-users at mcs.anl.gov
> Subject: Re: [petsc-users] Valgrind Errors
> 
> I'll check it.
> Hong
> 
> On Fri, Sep 12, 2014 at 3:40 PM, Dominic Meiser <dmeiser at txcorp.com>
> wrote:
> > On 09/12/2014 02:11 PM, Barry Smith wrote:
> >>
> >>     James (and Hong),
> >>
> >>      Do you ever see this problem in parallel runs?
> >>
> >>      You are not doing anything wrong.
> >>
> >>      Here is what is happening.
> >>
> >> MatGetBrowsOfAoCols_MPIAIJ() which is used by
> >> MatMatMult_MPIAIJ_MPIAIJ() assumes that the VecScatters for the
> >> matrix-vector products are
> >>
> >>    gen_to   = (VecScatter_MPI_General*)ctx->todata;
> >>    gen_from = (VecScatter_MPI_General*)ctx->from data;
> >>
> >> but when run on one process the scatters are not of that form; hence
> >> the code accesses values in what it thinks is one struct but is
> >> actually a different one. Hence the valgrind errors.
> >>
> >> But since the matrix only lives on one process there is actually
> >> nothing to move between processors hence no error happens in the
> >> computation. You can avoid the issue completely by using MATAIJ
> >> matrix for the type instead of MATMPIAIJ and then on one process it
> automatically uses MATSEQAIJ.
> >>
> >> I don’t think the bug has anything in particular to do with the
> >> MatTranspose.
> >>
> >>    Hong,
> >>
> >>      Can you please fix this code? Essentially you can by pass parts
> >> of the code when the Mat is on only one process. (Maybe this also
> >> happens for MPIBAIJ matrices?) Send a response letting me know you
> saw this.
> >>
> >>     Thanks
> >>
> >>       Barry
> >
> > I had to fix a few issues similar to this a while back. The method
> > VecScatterGetTypes_Private introduced in pull request 176 might be
> > useful in this context.
> >
> > Cheers,
> > Dominic
> >








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