[petsc-users] Fwd: MatZeroRowsColumns for mpibaij

Matthew Knepley knepley at gmail.com
Mon Nov 11 06:31:14 CST 2013

On Mon, Nov 11, 2013 at 5:33 AM, Stephan Kramer <s.kramer at imperial.ac.uk>wrote:

> On 01/11/13 06:01, Matthew Knepley wrote:
>  On Wed, Oct 30, 2013 at 9:19 PM, Rhodri Davies <rhodri.davies at anu.edu.au<mailto:
>> rhodri.davies at anu.edu.au>> wrote:
>>     Dear all,
>>     Would you mind giving us an update on your thoughts re: this
>> question? We're very keen to be able to use such functionally and it would
>> be good to know if you're looking into this / have any
>>     suggestions?
>> I looked at the code. It does not look hard to make a MPIBAIJ version.
>> Since the scatter context for BAIJ is already exploded, most
>> of the MPIAIJ code goes straight through, it just a matter of handling
>> the blocking in a few places.
>> Here is what would be really helpful for us. Write a nice test. The code
>> would probably only take an hour of being careful. However,
>> the test assembly would be more. If you give us a nice test example for
>> it, writing it could happen pretty quickly.
>>    Thanks,
>>      Matt
> That would be great. I had a look at the existing tests and found
> src/mat/examples/tests/ex140.c which already claims to test
> MatZeroRowsColumns with MPIBAIJ - except it isn't being run in parallel.
> Would running this test in parallel be a sufficient test to work with? It
> currently fails with the expected message "No support for this operation
> for this object type!". I'd be happy to write another test but it would
> basically be creating another matrix and testing it does the right thing
> with the matrix and the rhs. Let me know if there's anything else we could
> help out with

As far as I can tell ex140 does not really work. I am using ex12 to check
my rewrite of MatZeroRows(). I would like
a companion to that which uses RowsColumns(). And the work here is to
provide the output to check against. Even
for ex140 I would have to do that, which means more time here.


> Cheers
> Stephan
>  From: Stephan Kramer <s.kramer at imperial.ac.uk>
>>> Subject: Fwd: [petsc-users] MatZeroRowsColumns for mpibaij
>>> Date: 31 October 2013 13:16:05 GMT+11:00
>>> To: Rhodri Davies <rhodri.davies at anu.edu.au>
>>> -------- Original Message --------
>>> Subject: [petsc-users] MatZeroRowsColumns for mpibaij
>>> Date: Wed, 19 Jun 2013 13:22:31 +0100
>>> From: Stephan Kramer <s.kramer at imperial.ac.uk>
>>> To: PETSc users list <petsc-users at mcs.anl.gov>
>>> Dear all,
>>> We have found the MatZeroRowsColumns() routine to be very useful for
>>> lifting boundary conditions. Unfortunately we also found that it isn't
>>> implemented for matrix type mpibaij and we're quite keen on
>>> keeping the baij structure as it seems to give us significant savings
>>> for DG problems (in particular the blocked sor). I had a quick look at the
>>> implementation of MatZeroRowsColums_MPIAIJ but couldn't
>>> really estimate how hard it would be to do something similar for mpibaij
>>> (an implementation for seqbaij exists already). Is this something that's
>>> likely to be looked at in the future?
>>> Stephan

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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