[dune-pdelab] P2 in parallel - supplementary information

[Volker Schauer]

Maybe I should reformulate my question and give some additional
information about the way I am setting up the problem.

I use the P2 elements in a nonoverlapping setting, given by the alugrid.
In principal I use the solver 

Dune::PDELab::ISTLBackend_NOVLP_CG_SSORk<PGOS> 

to solve the problem, where I find that the solver converges, but the
tested residuum is not zero.

As input to the solver, I give an "consistent vector" which has the same
value on processor boundary nodes on all processes but arbitrary values
on the ghost nodes (is that correct or should these values also be the
same as their interior complements ?) and I also expect to get such an
consistant vector in the solution.

So my question is, whether the upper assumptions are correct or if there
might be a reason in pdelab why the P2 don't work, e.g. due to
missing/incorrect communication.

I hope this explains my problem sufficiently

Thanks

Volker

Am Mittwoch, den 14.12.2011, 12:22 +0100 schrieb schauer:
> Dear dune-pdelab,
> 
> does the parallel implementation of 3-dimensional P2 elements work fine
> in pdelab ?
> 
> I am solving the 3D Poisson problem in parallel using alugrid. With P1
> elements in parallel everything works fine and gives me the same
> solution as on a single process. When switching to P2 (where I only
> change the gridfunction space) the solver still tells me that the
> residual is zero, but when I actually calculate it by hand it is quite
> large. This is often the case if things on the boundary/ghost nodes goes
> wrong.
> 
> Does anybody have experience with 3D P2 elements ?
> 
> Thanks for your answers
> 
> Volker
> 
> 
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Volker Schauer (Dipl.Phys)

Institute of Applied Mechanics (Civil Engineering), Chair 1
University of Stuttgart
Pfaffenwaldring 7
D-70569 Stuttgart
GERMANY

Phone ++49 (0)711-68560044
email: schauer at mechbau.uni-stuttgart.de