[petsc-dev] DMDA_*PERIODIC and DMDA_XYZGHOSTED

[Barry Smith]

On Dec 7, 2010, at 1:59 PM, Jed Brown wrote:

> On Tue, Dec 7, 2010 at 20:53, Barry Smith <bsmith at mcs.anl.gov> wrote:
> BTW: I consider the DMDA Vec just a very special case that gets way to much attention and can sometimes distort the overall design of PETSc in issues that are not important in that non-special case.
> 
> Along these lines, I'm curious about using an API like VecGhost for the DA.  

   Interesting suggestion. 

> That is, what if there was a level where a Vec could know about a local form.  When you get the local form, one implementation would return the contiguous local form (no copy) and another implementation would return a separate vector.  

  How with the DMDA could you have a no copy and still allow nice 2 d and 3d array access of ghost points? It seems to me with DMDA you would always need a copy (or some crazy overloading of [])? Or do you mean in the DMDA case you get a copy but in the unstructured grid case you get no copy, but the basic paradigm of "local form" is always used? 


   Barry

> Then you could VecUpdateVector(Xglobal,Xlocal,imode,scattermode) or so (need an unambiguous name).  Then DMComposite could operate without forcing separate local and global vectors.

  In other words all parallel Vecs could have related local forms and the model is "give me local form Vec", scatter to/from local form vec etc? 

   Barry

> 
> Jed