[petsc-dev] Adding DMLocalToLocalBegin/End: What about PetscSF?

[Matthew Knepley]

On Mon, Jul 8, 2013 at 4:16 PM, Richard Tran Mills <rtm at eecs.utk.edu> wrote:

> Hi Jed,
>
> Revisiting this now; thanks for your help so far.  I understand that I can
> use PetscSFBcast() for this, but it is not clear to me whether there is a
> good way that I can make use of the "default" SF that exists (or the
> "default" PetscSection used to construct this).  Should I just construct
> some other "default" for local-to-local, or is there a good way to remap
> the "global" vector layout onto a local one?
>

The section stuff will not help you much, because you would still need to
create a mesh point SF. Its useful if you want to manage all data that way.

   Matt


> --Richard
>
> On 6/12/13 11:25 AM, Jed Brown wrote:
>
>> Richard Tran Mills <rtm at eecs.utk.edu> writes:
>>
>>  PETSc developers,
>>>
>>> I am finally getting around to adding the DMLocalToLocalBegin/End
>>> routines
>>> that I had mentioned several months ago.  Looking at
>>> DMGlobalToLocalBegin() in src/interface/dm/dm.c, I see that a little over
>>> a year ago, Matt added the use of a default 'PetscSF' ("star forest") if
>>> present to handle the global-to-local and local-to-global operations.  I
>>> am not familiar with PetscSF, but I assume that it should be possible to
>>> use these somehow (maybe needing to add a little bit of code) for
>>> local-to-local operations, since the communication pattern is the same as
>>> for a global-to-local.  Could someone who is familiar with PetscSF
>>> comment
>>> on this?
>>>
>> You can use PetscSFBcast for this.  For each point (which will be a leaf
>> in star-forest terminology), set the (rank, offset) of the owner
>> ("root").  Use PetscSFSetGraph rather than PetscSFSetGraphLayout,
>> because you don't have a global ordering/PetscLayout to use the latter.
>>
>
>
> --
> Richard Tran Mills, Ph.D.
> Computational Earth Scientist      | Joint Assistant Professor
> Hydrogeochemical Dynamics Team     | EECS and Earth & Planetary Sciences
> Oak Ridge National Laboratory      | University of Tennessee, Knoxville
> E-mail: rmills at ornl.gov  V: 865-241-3198 http://climate.ornl.gov/~**rmills<http://climate.ornl.gov/~rmills>
>
>


-- 
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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