[petsc-users] Behavior of KSP iterations when using Restart

[Nicolas Garcia Guzman]

Hello,


I am solving a linear system using petsc4py, with the following command:


python main.py -ksp_type gmres -ksp_gmres_restart 16 -ksp_max_it 180000 -ksp_monitor -ksp_converged_reason -ksp_rtol 1e-15 -pc_type asm -sub_pc_type ilu -sub_pc_factor_levels 1 -sub_ksp_type preonly


In the script all I do is import the libraries, load the linear system, set options and solve.


However, simply changing the restart parameter to something like 20, will make the solution iterate to exactly 2 times the restart parameter, and then say the iteration diverged. This happens every time no matter the parameter chosen, unless it's 16 or less. Is this expected behavior or is the problem coming from my linear system?
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