
<html>The <a rel="noopener" target="_blank" href="https://petsc.org/release/docs/manual/ksp/#multigrid-preconditioners">documentation</a> says that<br /><br />> The multigrid routines, which determine the solvers and interpolation/restriction operators that are used, are mandatory.<br /><br />But using code that doesn't contain any multigrid-specific routines e.g. ex45 and running it with<br /><br />-da_grid_x 129 -da_grid_y 129 -da_grid_z 129<br />-pc_type mg<br />-pc_mg_type multiplicative<br />-pc_mg_cycle_type v<br />-pc_mg_levels 5<br />...<br /><br />seems to work fine and also not fall-back to algebraic multigrid/PCGAMG from what I see with -log_view.<br /><br />What interpolation/restriction operators are used by default with PCMG?<br />Is it cleverly using the geometric information from DA?<br /><br />Thanks,<br />Paul<br /> </html>