Dear all, I don't know if this is a bug, but I observed that when using GMRES with AGG-PCGAMG as preconditioner Dirichlet boundary conditions don't seem to be exactly fulfilled.
My Matrix has zero rows and cols with 1 on the diagonal where I have dirichlet-bcs in my FE-mesh and I would expect that the eqs in this rows can be exactly fulfilled (as u_i = g_i) there. However, when I solve A*x = b with the above solver I only get u_i = g_i + error in that part of the vector. Switching from pc_gamg_type agg to pc_gamg_type classical cures this problem, but the classical is not advertised in the user manual. These are the options I'm currently using: -ksp_type gmres -ksp_pc_side right -pc_type gamg -pc_gamg_type agg [or classical] -pc_gamg_sym_graph 1 -pc_gamg_square_graph 1 -pc_gamg_agg_nsmooths 1 -pc_gamg_threshold 0.01 -pc_mg_cycles v Iteration counts are basically the same. Best regards Elias -- Dr. Elias Karabelas Research Associate University of Graz Institute of Mathematics and Scientific Computing Heinrichstraße 36 A-8010 Graz Austria Phone: +43 316 380 8546 Email: elias.karabe...@uni-graz.at<mailto:elias.karabe...@uni-graz.at> Web: https://ccl.medunigraz.at/
