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

[Matthew Knepley]

Yes, definitely. I have been too lazy to add names, but this is exactly
what is needed.

  Matt

On Wed, May 12, 2010 at 1:19 PM, Jed Brown <jed at 59a2.org> 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
>



-- 
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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