[petsc-dev] DMDA_*PERIODIC and DMDA_XYZGHOSTED

[Dmitry Karpeev]

This would require the analog of MatMatMult for scatters.
It shouldn't be that hard (if only MatScatter supported some way of getting
out the "values").


On Tue, Dec 7, 2010 at 3:47 PM, Jed Brown <jed at 59a2.org> wrote:

> On Tue, Dec 7, 2010 at 22:37, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
>
>> I may be out on a limb here, but the column DM could also encapsulate the
>> scatter
>> that currently sits in the Mat object. By default the row DM could have an
>> identity (noop) scatter.
>>
>> Note that this is very natural from the DD standpoint: ASM/GASM/FieldSplit
>> already define scatters that
>> scatter to a "subdomain" on which a  matrix/pc operate.  Currently, the
>> VecScatter inside the subdomain Mat
>> will further scatter the Vec to the "local" part, on which the matrix then
>> operates locally.  If the scatter is moved
>> out of Mat and into its column DM, than this double scatter can be
>> avoided.
>>
>
> Hmm, now the DM is starting to know a lot.  There are times where I think
> fusing scatters is good, but this one sounds tricky.  How would you
> implement this?
>
>
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