[petsc-users] error with version 3.17.1

Randall Mackie rlmackie862 at gmail.com
Tue May 3 16:55:48 CDT 2022

> On May 3, 2022, at 12:37 PM, Mark Adams <mfadams at lbl.gov> wrote:
>> Are you saying that now you have to explicitly set each 3x3 dense block, even if they are not used and that was not the case before?
> That was always the case before, you may have misinterpreted the meaning of a Mat block size?
> Actually block size is really more of a hint in that you don't have to set 3x3 dense blocks and thus any AIJ matrix can have any block size essentially.
> At least that is my understanding.
> There is a CI test that has sparse blocks and I ran into this issue with GAMG optimizations.
> (I had to add complicated code that Pierre actually found a bug in.)
> I don't know what changed in PETSc to make ASM fail for you, but if MatConvert and ASM fail then PETSc is broken and always has been.
> I did not follow this whole thread, but Randall could you change your code to add dense blocks or not use block size?
> Sorry, but I just don't think we should support this (Pierre seems to think that we do not) and we should "depreciate" this.
> This needs to be discussed of course.
> Mark

Hi Mark and Pierre,

You are correct that it is not necessary to use the block size. I had done that many many years ago because for some reason I thought it was necessary when creating a matrix for a 3D grid with more than 1 degree of freedom per node.

But as long as the matrix entries are set correctly, block size doesn’t really matter.

I think part of the issue in my situation is that there are parts of the matrix where not all 3x3 dense blocks are set due to representing a staggered grid system using a 3D DMDA (but like I say this was done many years before DMStag was developed).

Thanks for the help and the clarifications,


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