[petsc-users] Valgrind Errors

[Hong]

James :
I'm fixing it in branch
hzhang/matmatmult-bugfix
https://bitbucket.org/petsc/petsc/commits/a7c7454dd425191f4a23aa5860b8c6bac03cfd7b

Once it is further cleaned, and other routines are checked, I will
patch petsc-release.

Hong

> 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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