[petsc-dev] Need mechanism to set LocalToGlobal mapping in a DMShell

[Barry Smith]

On Feb 21, 2013, at 3:31 PM, Richard Tran Mills <rtm at eecs.utk.edu> wrote:

> I will add DMShellSetGlobalToLocal (and DMShellSetLocalToGlobal).
> 
> One other thing: We also need to be do LocalToLocal operations. For the structured grid case, we call DMDALocalToLocalBegin/End, and for the unstructured grid case we construct our own VecScatter context essentially just how it is done in daltol.c for DMDA.  Is there a good reason that there is no DMLocalToLocalBegin/End?

  I don't think so. Just laziness in not moving them over when DM was created from DA. You can add them.

   Barry

> 
> --Richard
> 
> On 2/21/13 2:42 PM, Barry Smith wrote:
>> On Feb 21, 2013, at 1:39 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>> 
>>> On Thu, Feb 21, 2013 at 1:31 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>> I don't understand.  There is a DMGlobalToLocalBegin/End() which includes
>>> 
>>>   } else {
>>>     ierr = (*dm->ops->globaltolocalbegin)(dm,g,mode == INSERT_ALL_VALUES ? INSERT_VALUES : (mode == ADD_ALL_VALUES ? ADD_VALUES : mode),l);CHKERRQ(ierr);
>>>   }
>>> 
>>>  For Shell, Richard should be able to provide his own begin/end functions. Which in his case he is already calling the VecScatterBegin/End() directly in his code so he should just be able to keep the scatter context he is already creating and use it in shell.  No reason to mess with sections or SF, he already has the scatter and just needs to get it into the DMShell and shell should have it as a matter of course. Just because everyone was to lazy to add DMSetGlobalToLocalBegin/End() doesn't mean it should exist. Rich can add it himself trivially and then use (even from Fortran).
>>> 
>>> 
>>> Yes, if he has VecScatters already that he wants to reuse, this is a fine option. I proposed this interface earlier in this thread.
>>> 
>>> DMShellSetGlobalToLocal(DM dm,PetscErrorCode (*begin)(DM,Vec,InsertMode,
>>> Vec),PetscErrorCode (*end)(DM,Vec,InsertMode,Vec));
>>    Ok, Richard should add this and then end of conversation.
>> 
>>    Barry
>> 
> 
> 
> -- 
> 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
>