Hello, 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.
Regards, Lukasz
