[petsc-users] Use of LSC preconditioning

[Matthew Knepley]

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/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20221111/79d0ee35/attachment.html>