[dune-fem] problem with diagonal precond and istl

[Andreas Dedner]

Hi.
There is a problem when setting the parameter
stl.preconditioning.method: jacobi
(for example in fem-poisson). An exception is thrown

Error: NotImplemented
[applyToISTLBlockVector:/home/dedner/TRUNK/dune-fem/dune/fem/solver/diagonalpreconditioner.hh:46]:
preconditioning not possible for non-assembled operators

Q1: the problem seems to be that the ISTLMatrixObject is used to check
if it is an assembled
       operator but that class is not derived from AssembledOperator -
that class also
       formally wants DF and the ISTLMatrixObject only knows DFS.
Q2: why is the dune-fem implementation used instead of the istl internal
one.
       Interestingly enough I even have
       fem.preconditioning: false

Best
Andreas