[petsc-users] restricted DMDAGlobaltoLocal

[Barry Smith]

On Nov 21, 2011, at 9:39 AM, Hui Zhang 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.  


Yes, we always communicate all ghost points, not just the boundary of the ghosted domain. Sorry I miss understood your earlier question.

It may be possible to modify the DMDA to communicate only the boundary but would require mucking around with the details of the code a bit. 

   Barry