[petsc-users] Fieldsplit on MATNEST

[Matthew Knepley]

On Wed, Nov 1, 2023 at 9:32 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Nov 1, 2023 at 3:59 PM Tang, Qi via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> Hi,
>>
>> I have a block matrix with type of MATNEST, but can I call
>> -pc_fieldsplit_detect_saddle_point to change its IS? I assume it is not
>> possible.
>>
>
> The detection part will work since MatGetDiagonal() is supported, but we
> do not have code in there
> to take arbitrary blocks from MATNEST since the whole point is to get
> no-copy access. Detection is
> not needed in the case that the blocks line up.
>
>
>> Also, I notice there is a small but important typo in the new fieldsplit
>> doc:
>> https://petsc.org/release/manualpages/PC/PCFIELDSPLIT/
>> The first matrix of the full factorization misses A10. I believe it
>> should be
>> [I -ksp(A00) A01]
>> [                I        ]
>>
>
> Yes, that is right.
>

Fixed: https://gitlab.com/petsc/petsc/-/merge_requests/6993

  THanks,

    Matt


>   Thanks,
>
>      Matt
>
>
>> Best,
>> Qi
>>
>
>
> --
> 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.cse.buffalo.edu/~knepley/>
>


-- 
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.cse.buffalo.edu/~knepley/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20231103/af9fe235/attachment-0001.html>