Hello I encountered different convergence behaviour of Newton Raphson when using different solver settings with PETSc
For the first solver configuration, I used direct solver -ksp_type preonly -pc_type lu -pc_factor_mat_solver_package mumps -mat_mumps_icntl_1 6 -mat_mumps_icntl_4 3 -mat_mumps_icntl_7 4 -mat_mumps_icntl_14 40 -mat_mumps_icntl_23 0 The simulation can run completely and the NR typically converged after 6/7 iterations. Of course, it's very slow. For the second solver configuration: -ksp_type gmres -ksp_max_it 300 -ksp_gmres_restart 300 -ksp_gmres_modifiedgramschmidt -pc_view -pc_fieldsplit_type multiplicative -fieldsplit_u_pc_type hypre -fieldsplit_u_pc_hypre_type boomeramg -fieldsplit_u_pc_hypre_boomeramg_coarsen_type PMIS -fieldsplit_u_pc_hypre_boomeramg_strong_threshold 0.6 -fieldsplit_u_pc_hypre_boomeramg_max_levels 25 -fieldsplit_wp_ksp_rtol 1.0e-8 -fieldsplit_wp_pc_type hypre -fieldsplit_wp_pc_hypre_type boomeramg -fieldsplit_wp_pc_hypre_boomeramg_coarsen_type PMIS -fieldsplit_wp_pc_hypre_boomeramg_strong_threshold 0.6 -fieldsplit_wp_pc_hypre_boomeramg_max_levels 25 The solver runs much faster, but the NR does not converge in 30 iterations after some time steps. I thought setting the solver tolerance -ksp_rtol 1.0e-12 but it doesn't help much because GMRES already terminate with tolerance 1e-30 (see sample log file). Can we set the tolerance of the sub-ksp of the Fieldsplit? I tried -fieldsplit_wp_ksp_rtol 1.0e-8 but it doesn't work. Sorry this problem is run with many time steps and is quite big so I cannot reproduce in a simple test case. Giang
sample_log_iteration
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