[dune-fem] Problems with dune-fem-howto tutorial

[Sacconi, Andrea]

Hi everyone,

I am playing with one of the tutorial programmes contained in dune-fem-howto.
It's the well-known Poisson equation, but there is something that is puzzling me.

Here are my questions:
1) if you modify the choice of the discrete function from Dune::AdaptiveDiscreteFunction to Dune::Fem::ISTLBlockVectorDiscreteFunction, is it necessary to modify Dune::Fem::SparseRowMatrixTraits with Dune::Fem::ISTLMatrixTraits for the matrix traits? The problem is, if I don't do that, I get a weird error with MatrixAdapter.
2) can we expect more or less the same amount of time spent on assembling the matrices? Because in the latter case, it seems that the assembling is 7 times slower than in the former case. How come?
3) I can't get the usual L2 and H1 orders of convergence anymore with Dune::Fem::ISTLBlockVectorDiscreteFunction and Dune::Fem::ISTLMatrixTraits. Where am I wrong?

I need ISTL data structures since, afaik, it's the only one for which a BiCGStab iterative algorithm is available.
I would really appreciate if you could shed some light on this matter!

Thanks a lot in advance!
Andrea
__________________________________________________________

Andrea Sacconi
PhD student, Applied Mathematics
AMMP Section, Department of Mathematics, Imperial College London,
London SW7 2AZ, UK
a.sacconi11 at imperial.ac.uk