[petsc-users] Use of LSC preconditioning

[Alexander Lindsay]

That makes sense. Thanks for the quick reply!

On Fri, Nov 11, 2022 at 2:59 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Fri, Nov 11, 2022 at 5:57 PM Alexander Lindsay <
> alexlindsay239 at gmail.com> wrote:
>
>> Under what conditions can I use LSC preconditioning for field split
>> problems with Schur? Let's imagine that all I've done is called
>> SNESetJacobian with global A and P and provided the index sets for 0 and 1.
>> Based off of the documentation on the man page
>> https://petsc.org/release/docs/manualpages/PC/PCLSC/ it seems like I'd
>> have to do something more programmatically, e.g.
>>
>>    PetscObjectCompose((PetscObject)Sp,"LSC_L",(PetscObject)L);
>>    PetscObjectCompose((PetscObject)Sp,"LSC_Lp",(PetscObject)Lp);
>>
>> If I try to naively get LSC preconditioning from the command line without
>> doing something like the above, then I get SUBPC_ERROR. Is this to be
>> expected?
>>
>
> Yes. PETSc does not have information about the operators or
> discretizations, and thus it cannot make auxiliary operators like the
> pressure Laplacian.
>
>   Thanks,
>
>      Matt
>
>
>>  0 Nonlinear |R| = 4.164062e-02
>>       0 Linear |R| = 4.164062e-02
>>   Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
>>                  PC failed due to SUBPC_ERROR
>>
>
>
> --
> 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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