[dune-pdelab] P2 in parallel - small correction

[Volker Schauer]

Am Donnerstag, den 15.12.2011, 10:27 +0100 schrieb 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

I don't have the ghost dofs with arbitrary values, but values are set to
zero by

Dune::PDELab::set_constrained_dofs(cc,0.0,rhs_poiss);

where the constraints container cc contains also the ghost nodes.  


Sorry for increasing your mail box needlessly

Volker

> 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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> > dune-pdelab at dune-project.org
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> 

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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