[Dune] load balancing ALUCubeGrid with metis

[Marco Cisternino]

Hi duners,
I would like to better understand what metis and alugrid do to 
loadbalance my grid, because I'm experiencing something weird to me (but 
probably normal to you).
I set a coarse 3D grid using ALUCubeGrid with 27 elements (3^3).
I attach a label to the central element and I pass the label to its 
sons. By this way I can refine this element and its sons as much times 
as I want.
I do it 3 times. Moreover I introduce a constraint: there cannot be more 
than 1 level of refinement between neighbour elements. This spreads the 
refinement to the other elements.
I balance (2 processes) the grid after every AMR, using Metis method 12 
and ldb_under=0.0 and ldb_over=1.2.
After the first and the second refinement everything works in the right 
way: the grid is partitioned among the processes well enough.
But after the third one, metis gives all the grid to process 0 and 
nothing to process 1.
Could anyone explain me why? Can I avoid this situation? Where can I 
find an exhaustive explanation of the metis parameters in alugrid.cfg file?
I'm using dune 2.1.1, alugrid 1.50 and metis 5.0.2.

Thanks a lot for any help.

Bests,

Marco

-- 
Marco Cisternino
Optimad Engineering s.r.l.
www.optimad.it
marco.cisternino at optimad.it
+3901119719782