[petsc-dev] field split/schur complement, incompressible flow

[Lisandro Dalcin]

On 12 May 2010 13:17, Jed Brown <jed at 59a2.org> wrote:
> On Wed, 12 May 2010 09:32:23 -0500, Chris Kees <christopher.e.kees at usace.army.mil> wrote:
>> Thanks a lot. Does PCFieldSplitSetFields() implicitly number the
>> fields it creates or am I missing something more fundamental e.g.
>>
>> PCFieldSplitSetFields(pc,isPressure)// field 0 for pressure
>> PCFieldSplitSetIS(pc,isVelocity)//field 1 for the 3 velocity components
>
> You use *either* PCFieldSplitSetFields() or PCFieldSplitSetIS().  If
> your matrix has a "block size" (e.g. it's BAIJ or you called
> MatSetBlockSize) then you can define the split at runtime:
>
>  -pc_fieldsplit_0_fields 0     # pressure is in the first split
>  -pc_fieldsplit_1_fields 1,2,3 # velocity in the second split
>
> You can set this programmatically with, e.g.
>
>  PCFieldSplitSetFields(pc,1,(PetscInt[]){0});
>  PCFieldSplitSetFields(pc,3,(PetscInt[]){1,2,3});
>
> If your spatial discretization does not have a natural block size, you
> should call PCFieldSplitSetIS() for both fields.
>

Chris is going to use this from Python, and I have to add support in
petsc4py. I think I'll have to provide a better API, something like:

pc.fieldSplitSetFields(0,[1,2,3],4) # (rho,[Ux,Uy,Uz],p)

or

pc.fieldSplitSetIS(is_rho, is_U, is_p)

and implement then by calling PCFieldSplitSet{Fields|IS} multiple times.

Does this API make sense?



-- 
Lisandro Dalcin
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