[petsc-dev] DMDA_*PERIODIC and DMDA_XYZGHOSTED

[Dmitry Karpeev]

As far as I can tell, the "local form" idea implies some mesh with a stencil
or overlap behind a Vec,
which by itself is a purely algebraic construct. Does this mean that we are
injecting some geometry
into Vec's semantics?

On Tue, Dec 7, 2010 at 2:20 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Dec 7, 2010, at 1:59 PM, Jed Brown wrote:
>
> > On Tue, Dec 7, 2010 at 20:53, Barry Smith <bsmith at mcs.anl.gov> wrote:
> > BTW: I consider the DMDA Vec just a very special case that gets way to
> much attention and can sometimes distort the overall design of PETSc in
> issues that are not important in that non-special case.
> >
> > Along these lines, I'm curious about using an API like VecGhost for the
> DA.
>
>    Interesting suggestion.
>
> > That is, what if there was a level where a Vec could know about a local
> form.  When you get the local form, one implementation would return the
> contiguous local form (no copy) and another implementation would return a
> separate vector.
>
>   How with the DMDA could you have a no copy and still allow nice 2 d and
> 3d array access of ghost points? It seems to me with DMDA you would always
> need a copy (or some crazy overloading of [])? Or do you mean in the DMDA
> case you get a copy but in the unstructured grid case you get no copy, but
> the basic paradigm of "local form" is always used?
>
>
>   Barry
>
> > Then you could VecUpdateVector(Xglobal,Xlocal,imode,scattermode) or so
> (need an unambiguous name).  Then DMComposite could operate without forcing
> separate local and global vectors.
>
>   In other words all parallel Vecs could have related local forms and the
> model is "give me local form Vec", scatter to/from local form vec etc?
>
>   Barry
>
> >
> > Jed
>
>
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