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

[Barry Smith]

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

>