[petsc-users] How can I retrieve the IS for all Missing Diagonal entries?

Matthew Knepley knepley at gmail.com
Wed Nov 22 10:26:08 CST 2017

On Wed, Nov 22, 2017 at 11:13 AM, Eric Chamberland <
Eric.Chamberland at giref.ulaval.ca> wrote:

> Hi,
> I have 2 questions:
> First, I am looking for a function that is almost like MatMissingDiagonal,
> but that would return me *all* missing diagonal entries.
> Does it exists?


> If not, is there another way of doing this?

Not a nice way, unfortunately. It is fairly dependent on the
implementation. You could call GetRow() for every row and check.

> Second: after searching through Petsc list, I found this that upset me a
> bit:
> https://www.mail-archive.com/petsc-users@mcs.anl.gov/msg22867.html
> so maybe I should modify our code to be fully compliant with this?  I have
> some examples (MUMPS) that are working without diagonal entries but I
> didn't tried other PCs or KSPs...

We use the diagonal frequently, for instance in the factorization PCs. I am
guessing we put in the diagonal when converting to the MUMPS format.



> Thanks,
> Eric

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

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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