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

[Chris Kees]

On May 12, 2010, at 12:19 PM, Jed Brown wrote:

> On Wed, 12 May 2010 13:27:18 -0300, Lisandro Dalcin  
> <dalcinl at gmail.com> wrote:
>> 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?
>
> Let's think about improving the C interface.  I would really like to
> name the splits since otherwise options sitting in petscrc files don't
> compose.  So what about
>
>  PCFieldSplitSetFields(PC,const char name[],PetscInt  
> nfields,PetscInt fields[]);
>  PCFieldSplitSetFieldsByName(PC,const char name[],PetscInt  
> nfields,const char *fieldnames[]);
>  PCFieldSplitSetIS(PC,const char name[],IS);
>
> and on the Python end, the direct wrappers could be called multiple
> times to set individual splits (if you provided direct wrappers) or  
> have
> the higher level interface using a dict
>
>  pc.FieldSplitSetSplits(splits)
>
> with any of the definitions
>
>  splits = dict(velocity=isvelocity, pressure=ispressure))
>  splits = dict(velocity=(0,1,2), pressure=(3,))
>  splits = dict(velocity=('u','v','w'), pressure='p')
>
> The latter would only work if the user used DMSetFieldName to identify
> fields u,v,w,p (recall that PC has access to the DM in -dev).  With  
> any
> of the definitions above, the runtime prefixes would be
> -fieldsplit_velocity_* and -fieldsplit_pressure_* instead of just
> numbers.
>
> Does this seem sensible?
>
> Jed

That makes sense to me.  I'm all for naming the fields, and the  
dictionary representation in python is very intuitive.

Chris