[petsc-users] restricted DMDAGlobaltoLocal

[Matthew Knepley]

On Mon, Nov 21, 2011 at 9:39 AM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:

>
> > On Nov 21, 2011, at 8:01 AM, Jed Brown wrote:
> >
> >> On Mon, Nov 21, 2011 at 04:52, Hui Zhang <buyong.huier at gmail.com>
> wrote:
> >> When using DMDAGlobaltoLocal, how can I communicate only the boundary
> of the
> >> ghosted domain (with stecil width larger than one)?
> >>
> >> Only the ghost values are communicated. The interior is all local.
> >
> >   I think Hui means DMDALocalToLocalBegin() and DMDALocalToLocalEnd()
> but normally one doesn't need this with the PETSc solvers, one only needs
> the DMGlobalToLocalBegin/End()
> >
> >   Barry
> >
>
> Thank you all!
>
> I'm actually implementing domain decomposition methods with restricted
> communication.
> From my understanding, DMDALocalToLocalXX is also communicating all ghost
> values of
> the second Vec. However, in a restricted way, only the ghost points most
> far away from
> the interior are communicated.


No, the communication pattern in the same. You exchange values which are
shared by multiple
processes. The difference is that LocalToLocal puts values directly into a
ghosted local vector,
whereas LoaclToGlobal puts them into a global vector, which is not ghosted.

   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
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