[petsc-dev] Add natural-to-global and global-to-natural operations for DM?

[Richard Tran Mills]

Hi Barry,

What we call the "natural" ordering in PFLOTRAN is what is referred to 
as the "application" ordering in PETSc parlance.  In the structured grid 
case this "application" ordering is the natural ordering used by the 
DMDA routines like DMDANaturalToGlobalBegin()/End(), and in the 
unstructured case it is whatever ordering was used to assign cell IDs 
when the unstructured grid was created.  Rather than having code for two 
cases, I would prefer to be able to just call 
DMNaturalToGlobalBegin()/End() for either case.  I do realize, of 
course, that for the DMDA case there is always a default meaning for the 
"natural" ordering, whereas for the case of a general DM the notion of 
"natural" will be application dependent and will have to be specified by 
user code (which I'd like to do in this case by having a 
DMShellSetNaturalToGlobalVecScatter()).

Obviously, there may be subtypes of DM for which no "natural to global" 
operation makes sense.  What I'm saying is that I nonetheless would like 
to have a general DMNaturalToGlobalBegin()/End() that will do the 
appropriate thing if it makes sense for that DM and complain otherwise.  
I guess this is a question of what the PETSc philosophy is regarding 
such things.  I note that there is at least one example of a current 
DMDA method that ought to just be a DM one: I don't see why we should 
have DMDALocalToLocalBegin()/End() and not just 
DMLocalToLocalBegin()/End(), and I'd like to go ahead and change this.  
But LocalToLocal makes sense for lots of DMs, and NaturalToGlobal may not.

--Richard

On 3/7/13 10:51 PM, Barry Smith wrote:
> On Mar 7, 2013, at 9:46 PM, Richard Tran Mills <rtm at eecs.utk.edu> wrote:
>
>> Continuing on my quest to be able to wrap all of the unstructured grid operations in PFLOTRAN inside a DM: Would it be OK to add DMGlobalToNaturalBegin()/End() and DMNatualToGlobalBegin()/End()? These are currently DMDA routines, not DM ones.  We do something that we call natural-to-global and global-to-natural operations with our unstructured grid cases in PFLOTRAN (though I'm not sure if "natural" is quite the thing to call it... I always think of that in terms of a structured grid layout).  I would like to just call DMGlobalToNaturalBegin()/End(), etc., on our DM, whether it is a DMDA or a DMShell.
>>
>> I had already mentioned that I plan to add DM interface routines for local-to-local operations.  I am thinking that global-to-natural, etc., also ought to be added, though I'm not sure if the concept of "natural" ordering necessarily makes sense in some cases.
>     What does natural mean for you on anything but a DA in what you do with pflotran? Once we all understand than we can come up with ideas on how that fits with DM.
>
>     Barry
>
>> --Richard
>>
>> -- 
>> 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
>>


-- 
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