On Wed, Jul 5, 2023 at 11:29 AM Khurana, Parv <[email protected]> wrote:
> Hello PETSc users, > > > > I am fairly inexperienced with PETSc as of now and am new to the mailing > list! Thanks for running this channel. > > > > I seek basic help regarding running AMG routines (BoomerAMG/ML/GAMG). I am > trying to compare the performance of solving a Poisson problem using a AMG > Preconditioned GMRES iterative solve vs using AMG as the solver. I use > PETSc options using the options database keys as of now, and it is > connected to a flow solver (Nektar++) I use for my research. > > > > I currently run the AMG Preconditioned GMRES iterative solve by setting > -ksp_type > gmres and then specifying the preconditioner I want using, for e.g, -pc_type > hypre -pc_hypre_type boomeramg. > Looks good. You need to configure with --download-hypre and you should be good to go. You can also try -pc_type gamg You can also try -pc_type ml If I want to use the AMG routine, I am currently setting -ksp_type preonly > and the same -pc_type. > I am not understanding this. You just said you use -ksp_type gmres. Stick with that! > However, I am not sure if this is correct way to go about it due to two > reasons: a) my solution using AMG as a solver with these options has a > larger error than AMG Preconditioned GMRES (which could still be > acceptable), and b) I could not find any clear documentation regarding how > to use AMG directly as a solver. I saw some hints in the examples here > https://petsc.org/main/tutorials/handson/# > <https://petsc.org/main/tutorials/handson/>, but it hasn’t helped me. > > > There are a lot of solver examples in the code base. eg, src/snes/tutorials/ex19.c: args: -da_refine 5 -snes_monitor -snes_converged_reason -pc_type hypre -dm_mat_type {{aij baij}} There are regression tests in a big comment block at the end of each example file. You can use these as examples. Good luck, Mark > Any hints on how to use AMG directly as a solver? > > > > Best > > Parv > > >
