I'm trying to reuse the PC constructed by GAMG during a sub-iterative procedure where KSPSolve is called with the same matrix repeatedly. The right-hand side changes during the sub-iteration. I've been attempting to use SAME_PRECONDITIONER for nit = 2..., but this seems to lead to very different results than using DIFFERENT_PRECONDITIONER each sub-iteration. I'm using the following options:
-pres_ksp_type preonly -pres_pc_type redistribute -pres_redistribute_ksp_type bcgsl -pres_redistribute_pc_type gamg -pres_redistribute_pc_gamg_threshold 0.01 -pres_redistribute_mg_levels_ksp_type richardson -pres_redistribute_mg_levels_pc_type sor -pres_redistribute_mg_coarse_ksp_type richardson -pres_redistribute_mg_coarse_pc_type sor -pres_redistribute_mg_coarse_pc_sor_its 5 -pres_redistribute_pc_gamg_type agg -pres_redistribute_pc_gamg_agg_nsmooths 1 -pres_redistribute_pc_gamg_sym_graph true -pres_redistribute_ksp_initial_guess_nonzero 0 Is there a dependence on the right-hand side in GAMG somewhere? John
