[Dune] Coarsening of ALUGrid very slow

[Uli Sack]

Hi Dune!

I have had an ALUGrid (sequential) of roughly 18mio nodes that was 
coarsened in two successive marking and adapting cycles to about 4.8mio 
nodes. This took about 14 hours (!!!) on a 64Bit SuSe10 system running 
on a machine with 256GB RAM (and 8...)
model name      : Dual-Core AMD Opteron(tm) Processor 8220
cpu MHz         : 2792.922
cache size      : 1024 KB
Same thing for about 9mio to 2.5mio nodes took round about 3,5h, 
4.9mio->1.3mio 24min. This has a somewhat quadratic feel.
Adding some stopwatches showed that more than 95% of that time goes into 
the preAdapt(),adapt(),postAdapt() cycle. I guess it actually goes into 
the adapth() method but I'm checking on that right now.

Would you happen to know where the implementation of the coarsening 
might cause quadratic (or let's say nonlinear) runtime?

tnx,
Uli
-- 
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* Uli Sack                     ** email: usack at math.fu-berlin.de       *
* Freie Universität Berlin     ** phone: + 49 (30) 838 75250           *
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