[petsc-users] matsetvaluesblocked4_

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Wed, May 27, 2020 at 7:09 PM Mark Adams <mfadams at lbl.gov> wrote:
>
>>
>>
>>>>
>>>> Matt: Could I use BAIJ with Plex?
>>>>
>>>
>>> Plex does this automatically if you have blocks.
>>>
>>
>> I use DMCreateMatrix with forest or plex and I seem to get AIJ matrices.
>> Where does Plex get the block size?
>>
>> I have not yet verified that bs is set in this matrix.
>>
>
> I think I may know what your problem is. Plex evaluates the blocksize by
> looking for an equal number of dofs
> on each point. This is sufficient, but not necessary. If you are using
> higher order methods, there is block structure
> there that I will not see.
>
> Jed, is there an obvious way to see that structure that I am missing?

gcd of all the point sizes.

Note that you don't have constant block sizes if you eliminate some
fields/components in boundary conditions.