[petsc-users] Multi level DM Shell

[Luc Berger-Vergiat]

Would there be a better option than a DMShell to do define fieldsplits of a matrix already assembled?
The matrix comes from an FEM code and has boundary conditions applied to it before it is passed to PETSc.
A DMShell seems like a good option since it does not require any particular knowledge on the underlying mesh of the problem.
But is there another DM type supporting the DMCreateSubDM function, can work on a matrix coming from an FEM unstructured quad mesh with BCs applied to it?
Maybe DMPlex? though I am not sure that FEM meshes can be described as Hasse Diagram all the time especial quad meshes...

Best,
Luc

On 3 févr. 2014, at 16:59, Matthew Knepley wrote:

> Yes
> 
>   Matt
> 
> 
> On Mon, Feb 3, 2014 at 3:32 PM, Luc Berger-Vergiat <lb2653 at columbia.edu> wrote:
> I'm fairly sure I know the answer to this question after looking up the source code but is it possible to create sub-splits while using a DMShell?
> To be more specific I have a matrix which I decompose into 4 fields and I would like to do something like
> 
> -ksp_type gmres
> -pc_type fieldsplit
> -pc_fieldsplit_type schur
> -pc_fieldsplit_schur_factorization_type full
> -pc_fieldsplit_schur_precondition self
> -pc_fieldsplit_0_fields 0,1
> -pc_fieldsplit_1_fields 2,3
> ...
> 
> Best,
> Luc
> 
> 
> 
> -- 
> 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

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