gmres - restart and Gauss-Seidel

Lukasz Kaczmarczyk lukasz at
Thu Aug 14 17:09:32 CDT 2008

I have implementation of geometric multi-grid for heterogeneous
quasi-brittle materials for hybrid-trefftz finite elements (degrees of
freedom are on faces -> small number of neighbours). Multi-grid
algorithm need smoothing, for that I use Gauss-Seidel, however SOR
implemented in PETSc is not parallel. That is way, I implemented my own
parallel Gauss-Seidel with colouring of faces in order to reduce
communication. Everything seems to work prefect, except that that for
GMRES after restart algorithm is divergent. With SOR implemented in
PETSc algorithm does not have this  problem. Can any give my tip how to
cure may problem.


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