[Trilinos-Users] [EXTERNAL] Re: Best practices for parallel solutions?

[Heroux, Michael A]

Paul,

You can use the exporter object, used to push data for use by the solver,
with the import method to get ghost data back.

Mike

On 12/13/11 8:30 AM, "Paul Dionne" <pjd at cfdrc.com> wrote:

>Also, what is the best way to get the ghost cell values after solving.
>After the parallel solution I have a solution vector {x} defined on a
>non-overlapping map.  I would like to get a vector {y} that contains the
>solution in the ghost cells as well as the real cells.  Thus, the target
>map would be an overlapping map, but if I understand the Export function
>correctly I cannot export to an overlapping map - is that correct?
>
>On 12/12/2011 4:18 PM, Nico Schlömer wrote:
>> Hi Paul,
>>
>> for solving nonlinear problems, you might want to take a look at the
>> NOX package as well. You specify the linear (Jacobian) operator once
>> (e.g., as an Epetra_FECrsMatrix as suggested by Mike), and NOX will
>> take care of all the rest. -- No need for you to think about whether a
>> copy would be efficient or not.
>>
>> --Nico
>>
>>
>>
>>
>> On Mon, Dec 12, 2011 at 9:56 PM, Paul Dionne<pjd at cfdrc.com>  wrote:
>>> I'd like to know the recommended practice for solving parallel linear
>>>systems.  I have an implicit finite-volume solver and thus I have ghost
>>>cell links during assembly.  I found a presentation entitled
>>>"HerouxEpetraConcepts.pptx" that suggested using an assembly map and a
>>>solver map.  After assembly, the following commands were given in the
>>>presentation:
>>>
>>> Epetra_Export Exporter(AssemblyMap, SolverMap);
>>> Epetra_CrsMatrix SolverMatrix(Copy, SolverMap, 0);
>>> SolverMatrix.Export(AssemblyMatrix, Exporter, Add);
>>> SolverMatrix.FillComplete();
>>>
>>> My problems are nonlinear so I solve the linear system several times
>>>each time step.  Thus, I was wondering about the efficiency and memory
>>>requirements of having 2 matrices and performing this matrix copy each
>>>time I solve.
>>>
>>> Is this the current recommended practice?
>>>
>>> I'd also like to know how best to get the ghost cell values after the
>>>solution (without doing it myself through MPI).  I'm trying to get it
>>>to work using Epetra_Export but not having much luck.
>>>
>>> Thanks for any assistance.
>>>
>>>
>>> _______________________________________________
>>> Trilinos-Users mailing list
>>> Trilinos-Users at software.sandia.gov
>>> http://software.sandia.gov/mailman/listinfo/trilinos-users
>>>
>
>-- 
>Paul J. Dionne
>Technnical Fellow
>CFD Research Corporation
>215 Wynn Drive, 5th floor
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