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

[Eric Chamberland]

Thank you for your answers.

First, I was wrong when telling that having empty rows is working for LU 
solver: after verification, it is the exact opposite: it does not work 
for MUMPS.

We have a nightly test that solve that kind of matrix with a 
gmres+jacobi combination and it works well...

Second, since LU solvers are interesting to use as the solvers for the 
coarsest level in a PCGAMG for example, we still have to give a non-zero 
for all the diagonal...

So my solution will be to add it anyway... :)

Thanks again,

Eric


On 22/11/17 11:26 AM, Matthew Knepley wrote:
> On Wed, Nov 22, 2017 at 11:13 AM, Eric Chamberland 
> <Eric.Chamberland at giref.ulaval.ca 
> <mailto: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?
> 
> 
> No
> 
>     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
>     <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,
> 
>      Matt
> 
>     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/>