[dune-pdelab] some problems in dune

[Robert Jendrny]

Moin moin,

I know that I changed the coarsentarget to 1 because this should be the 
advantage of AMG compared to GMG
Also with other coarsentarget values I got iteration numbers which were 
exploding ... the '1' was just an example output for you

If I change usesuperlu=false to usesuperlu=true I get the message: You 
are using AMG without superlu, please install it or set it to false
So where can I find superlu to install it on my pc

I think that AMG together with Q2 is not valid ;-)
The AMG algorithm should know that you are using Q2 in two dimensions 
... but the matrix structure is equal or nearly the same if you use Q1 
in three dimensions ...

I think I have to wait for Markus' answer :-)

Yours
Robert


On 10/31/2014 02:08 PM, Rebecca de Cuveland wrote:
> Hey,
>
> why did you change the coarsentarget parameter? The default is 
> somewhere at 1000 nodes, and it seems you have 1? That is certainly 
> not a reasonable choice. (You have only one unknown on your coarsest 
> level).
>
> I also see in your code that you do not use Superlu as solver on the 
> coarsest level (usesuperlu = false). As the warning that you 
> explicitly supress with this flag states: Use superlu, sometimes this 
> has a drastic impact on the solution.
>
> Does something change, when you use superlu and a coarsentarget of at 
> least 100 (or even more)?
>
> One last thing, we spoke about AMG in combination with Q2 today in our 
> group meeting:
> Nobody has really used this in pdelab, and we are not sure if the 
> implementation in istl is also valid for Q2. Perhaps Markus can say 
> something about that?
>
> Bye,
> Rebecca
>


-- 
Robert Jendrny
B.Sc. Technomathematik

TU Dortmund, Fakultät für Mathematik
LS III: Angewandte Mathematik und Numerik
M 1020, Vogelpothsweg 87, 44227 Dortmund
robert.jendrny at math.tu-dortmund.de