[petsc-dev] DMDA_*PERIODIC and DMDA_XYZGHOSTED

[Jed Brown]

On Tue, Dec 7, 2010 at 21:45, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:

> I think the idea of a function space is useful.
> In the default case it could be essentially a PetscLayout, which, I guess,
> could be wrapped up as a DM.
>

PetscLayout is just the decomposition, VecScatter encodes a lot more
information.  DM normally also has some VecScatters, but VecScatter is much
more general.  Flat Euclidean space requires no information that is not
already in the Vec.

One reason to always have a DM with a Vec is that we could implement
VecView(X,v) as DMVecView(X->dm,X,v) and if you wanted to interpret the Vec
as a member of a different space (e.g. you had a Vec from a DMDA and wanted
to view it "natively"), you would DMVecView(dmflat,X,v) which I find cleaner
than pushing and popping "formats".  Maybe dmflat would be a predefined
constant (instead of an object you had to define) or maybe just NULL, but I
think the current viewing model is pretty fragile/confusing and overly
dependent on how the Vec was created.

Jed
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