Dear all, I hope you're having a nice day. I have a quick question on solving Poisson equation with KSP solvers (/src/ksp/ksp/example/tutorial/ex29.c). Currently, I run this solver with: -pc_type gamg -ksp_type cg -pc_gamg_agg_nsmooths 1 -mg_levels_ksp_max_it 1 -mg_levels_ksp_type richardson -ksp_rtol 1.0e-7 It performs very well in parallel computation and scalability is fine. However, if I run it with a single process, the KSP solver is much slower than direct ones, i.e. Mudpack. Briefly, the speed difference between the KSP solver and the direct solver is negligible on dealing with small problems (i.e.36k DoFs ) but becomes very huge for moderate large problems (i.e. 180k DoFs). Although the direct solver inherently has better performance for moderate large problems in the single process, I wonder if any setup or approach can improve the performance of this KSP Poisson solver with the single process? or even make it obtain competitive speed (a little bit slower is fine) against direct solvers.
thanks in advance, Alan
