[dune-pdelab] solver for nonoverlapping grid decompositions

[Bernd Flemisch]

Dear Dune-PDELab,

last time I visited you in Heidelberg, Peter gave me the idea to improve
the available solver for the nonoverlapping case. I meanwhile
implemented it, the result is attached in form of a patch for
istlsolverbackend.hh, and a patch for nonlineardiffusion.cc from the
howto for testing it.

There are three parts:
1. VertexExchanger: based on dune-disc stuff, this is responsible for
adding up matrix entries. In contrast to dune-disc, only border vertices
are considered and no extra degrees of freedom have to be introduced.

2. NonoverlappingWrappedPreconditioner: pretty much the same as its
overlapping counterpart. In fact, the preconditioner is the same as for
the overlapping case with an overlap layer of one element width.

3. ISTLBackend_NOVLP_BCGS_SSORk: uses 1. and 2. to build the final solver.

It would be great if you find some time to look at it and maybe decide
to include it in dune-pdelab.

Kind regards
Bernd

-- 
_____________________________________________________________________

Bernd Flemisch                               phone: +49 711 685 69162
IWS, Universität Stuttgart                   fax:   +49 711 685 60430
Pfaffenwaldring 61                  email: bernd at iws.uni-stuttgart.de
D-70569 Stuttgart                  url: www.hydrosys.uni-stuttgart.de
_____________________________________________________________________

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