[petsc-users] Fieldsplit on MATNEST

[Matthew Knepley]

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.

  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/>
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