[petsc-dev] DMComplex and PCFieldSplit

[Matthew Knepley]

On Fri, Feb 24, 2012 at 2:39 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Feb 24, 2012, at 2:23 PM, Jed Brown wrote:
>
> > We need a richer field interface. Some way for a client of DM to
> discover vector and tensor structure.
>
>    No idea what a tensor is, but DMGetSubDMS(dm,PetscInt *cnt,IS *ises,DM
> *dms);   and DMPushSubDMType(DM,"name of a type of splitting like u,v,p or
> velocity,p"); DMPopSubDMType(); and DMGetAvailableSubDMTypes(DM,char **);
>
>  Do you need more than that?
>

Yuck Yuck Yuck. Why are we persisting in shoving all of the index stuff
into the DM interface. I think this is so
unwieldy and complicated. PetscSection is small, powerful, and does
everything suggested and more. I see
no argument in support of stuff like the above.

   Matt


>    Barry
>
> Note that current DMDA's default subdms served up would be a DM for each
> field consisting of one of the degrees of freedom per node and it could
> also serve up  DMs that represent any collections of those for example dof
> 0 and 1 per node, then dof 2 per node. We'll need to come up with some
> naming convention for these.
>
>
> > Possibly also (eventually) a way to solve equations of state so that we
> can formulate reduced problems in non-conservative variables.
> >
> > On Feb 24, 2012 2:19 PM, "Matthew Knepley" <knepley at gmail.com> wrote:
> > On Fri, Feb 24, 2012 at 1:58 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> > http://petsc.cs.iit.edu/petsc/petsc-dev/rev/518ff70e8a0a
> >
> > Matt, I want to get rid of these conditionals, not add more. We should
> have a DM base interface for getting fields on which to split, that common
> interface should _replace_ the DMComposite specialization.
> >
> > I agree. However, I won't put anything in until I do it by hand once.
> >
> > Also, I was tempted to just promote DMGetGlobalISes(), but its not quite
> right. I am planning
> > to put the IS method in PetscSection. I am hoping eventually DMDA uses
> PetscSection for
> > layout.
> >
> >    Matt
> >
> > --
> > 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
>
>


-- 
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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