Dmitry Karpeev karpeev at mcs.anl.gov
Tue Dec 7 15:40:37 CST 2010

And yet DMDA already defines this local fine-granularity "stencil" access.
Where would it go, if not in the DM?  In my opinion this is part of the
function space definition:
it generalizes VecGetArray to something more geometric.
Not all DMs have to implement this.

On Tue, Dec 7, 2010 at 3:35 PM, Jed Brown <jed at 59a2.org> wrote:

> On Tue, Dec 7, 2010 at 22:06, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
>> But those that *want* to know, can obtain the underlying DM and start
>> doing cool stuff
>> to the Vec.   In particular, DM is the natural place to inject geometric
>> information, generalizing DMDA to the unstructured
>> case.  For example, a DM can allow to access the Vec data by "stencil",
>> which in the DMDA case is the usual thing,
>> and in the unstructured mesh case is, say, element restrictions.  This
>> would encapsulate the "expanded space" idea
>> that Jed described a while ago in a tentative unstructured API.  This
>> would require, however, some iterator model,
>> which is a kind of flexible local fine-granularity "on demand" scatter.
> This functionality is all in Level 3 of my earlier message, it's not a part
> of the DM API that Vec should be aware of.
> The only parts of the DM API that I think Vec should be aware of is
> PetscLayout, the "overlap" scatters, and DMVecView.   The last one is purely
> cosmetic because VecGetDM, DMVecView is so common.
> Jed
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