[dune-pdelab] P2 in parallel - small correction

[Volker Schauer]

Hi Markus

The norm of the residual (calculated with novlpSP.dot) which on a single
process goes to values less then 10^-10 gives me now a value at the size
of >= 36000 and changing the tolerance of the solver basically does not
effect this.

I did not look at the residual in a greater detail, so maybe I should
check if it is large e.g. only on boundary nodes ? But how would I check
that, since I do not really know/understand the assignment of indices in
gridvectors like the residual to the entities of the grid with that
strange offset in Dune and so I do not know which of my indices belongs
to a boundary node. (If somebody could give here a "short" explanation,
I think this would be valueable by its own, also for other users). 
So I could iterate over the entities of e.g. codim 3 and find that one's
partition type is border, but now how do I find which index in the
grid-vector is assigned to that entity ? 


So I will try to extract the Poisson problem and send it to the mailing
list.

Thanks for your help (all pdelab members) - I really appreciate that

Volker 



-------- Weitergeleitete Nachricht --------
Von: Markus Blatt <markus at dr-blatt.de>
Reply-to: Markus Blatt <markus at dr-blatt.de>
An: Volker Schauer <schauer at mechbau.uni-stuttgart.de>
Kopie: dune-pdelab <dune-pdelab at dune-project.org>
Betreff: Re: [dune-pdelab] P2 in parallel - small correction
Datum: Fri, 16 Dec 2011 11:46:27 +0100

Hi,

On Fri, Dec 16, 2011 at 11:34:36AM +0100, Volker Schauer wrote:
> It would be helpful if someone says that he has already used the
> communication from PDELab to set up the Poisson or any other PDE
> successfully with P2 elements (I suppose this was tested in PDELab when
> the parallel use was implemented?). Would it help you or anybody else if
> I extract the Poisson problem (which is embedded in a larger code doing
> some more stuff) and send it to the mailing list ?
> 

Yes, that would help in two ways: giving us an easy test case and
checking whether there is a mistake in the usage of PDELab.

You were saying that your residual is not not zero. Would do you mean
by zero? Our solvers only achieve a relative residual reduction, so
this might happen if your intial residual is large.

Have you looked at the residual? If so, where does is deviate from the
expected values?

Cheers,
 
Markus


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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