[petsc-dev] MatGetLocalSubMatrix, MatLocalReference implementation

Barry Smith bsmith at mcs.anl.gov
Fri Nov 19 21:15:32 CST 2010

On Nov 19, 2010, at 6:43 PM, Jed Brown wrote:

> Jed
> [1] Barry, what is going on with DMCompositeGetLocalISs() and
> DMCompositeGetGlobalIndices().  

   Looks like code that was started (maybe from cut and paste) and never finished. The manual page for function has a different name then the function, like I just stopped in the middle of editing and forgot about it.
> The former has no implementation and the
> latter has no man page.  I do not think that "Local IS" is a good name
> for the global indices defined at all the local points (i.e. what
> GetGlobalIndices is returning, in an array of ISs).  The "Local IS" that
> I am looking for is the (serial) ISStride for each contiguous chunk of
> the local vector.  What about DMCompositeGetGhostedISs() for the thing
> GetGlobalIndices() is currently returning?

   Well no. Local always refers to things with ghost points, while global means without ghost points. You are asking to introduce another term "Ghosted" to mean with ghost points.  Confusing/bad to introduce more terminology.

   Now you could argue that using local and global was bad originally and we should use ghosted and global (or nonghosted) as our two terms. But introducing ghosted in just one place is not the solution, we would have to do it systematically through PETSc source and documentation. Though I think local and global are fine as is and don't see a need to change from local to ghosted.

  Or I could be misunderstanding what you want to change.


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