[petsc-users] Problem setting Fieldsplit fields

[Matthew Knepley]

On Fri, Feb 3, 2023 at 2:46 PM Nicolas Barnafi via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Dear community,
>
> I am using a fieldsplit preconditioner, but for some reason I cannot
> group fields as in other libraries (i.e. I do this in Firedrake and it
> works). Some context:
>
> I have set four fields to the preconditioner, which I want to regroup with
> -pc_fieldsplit_0_fields value: 0,1
> -pc_fieldsplit_1_fields value: 2,3
>

You should not have a colon, ":"

  Thanks,

     Matt


> But apparently this doesn't get read for some reason. In fact, from
> -ksp_view I still see all 4 fields, and it fails as one of the blocks
> has a null diagonal (coming from a saddle point problem), so it gives
> the following error. Interestingly, it shows that the groupings where
> not considered:
>
> [0]PETSC ERROR: Object is in wrong state
> [0]PETSC ERROR: Matrix is missing diagonal entry 0
> [0]PETSC ERROR: WARNING! There are option(s) set that were not used!
> Could be the program crashed before they were used or a spelling
> mistake, etc!
> [0]PETSC ERROR: Option left: name:-pc_fieldsplit_0_fields value: 0,1
> [0]PETSC ERROR: Option left: name:-pc_fieldsplit_1_fields value: 2,3
>
> Any clues to why this can happen? Best regards,
> Nicolás Barnafi
>
>

-- 
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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