Hi Mark, Thanks! I am not sure how to construct null space and zero energy modes manually for this operator. Is there some theory or documentation I can follow to figure out what the null space and zero energy modes look like for this operator? Once I know what these are in symbolic form, I think I should be able to construct them manually.
Best, --Amneet On Tue, Oct 29, 2024 at 7:35 AM Mark Adams <mfad...@lbl.gov> wrote: > Oh my mistake. You are using staggered grids. So you don't have a block > size that hypre would use for the "nodal" methods. > I'm not sure what you are doing exactly, but try hypre and you could > create the null space, zero energy modes, manually, attach to the matrix > and try GAMG. > You can run with '-info :pc' and grep on GAMG to see if GAMG is picking > the null space up (send this output if you can't figure it out). > > Thanks, > Mark > > On Tue, Oct 29, 2024 at 9:28 AM Mark Adams <mfad...@lbl.gov> wrote: > >> This coordinate interface is just a shortcut for vertex based >> discretizations with 3 dof per vertex, etc. (maybe works in 2D). >> You will need to construct the null space vectors manually and attach it >> to the matrix. Used by GAMG. >> >> Note, for hypre you want to use the "nodal" options and it does not use >> these null space vectors. That is probably the way you want to go. >> eg: -pc_hypre_boomeramg_nodal_coarsen >> >> I would run with hypre boomerang and -help and grep on nodal to see all >> the "nodal" options and use them. >> >> Thanks, >> Mark >> >> >> On Mon, Oct 28, 2024 at 8:06 PM Amneet Bhalla <mail2amn...@gmail.com> >> wrote: >> >>> Hi Folks, >>> >>> I am trying to solve the momentum equation in a projection >>> preconditioner using GAMG or Hypre solver. The equation looks like for >>> velocity variable *v* looks like: >>> >>> >>> [image: Screenshot 2024-10-28 at 4.15.17 PM.png] >>> >>> Here, μ is spatially varying dynamic viscosity and λ is spatially >>> varying bulk viscosity. I understand that I need to specify rigid body >>> nullspace modes to the multigrid solver in order to accelerate its >>> convergence. Looking into this routine MatNullSpaceCreateRigidBody() ( >>> https://urldefense.us/v3/__https://petsc.org/release/manualpages/Mat/MatNullSpaceCreateRigidBody/__;!!G_uCfscf7eWS!aMSTPnVUiWdbtpI6UINZH776-nK60U2dgj1Bdi0emhPwrO4arqfcByiLjc2h5-zJ200uYPq7HgtpUtfCgZLepbk2Fw$ >>> >>> <https://urldefense.us/v3/__https://petsc.org/release/manualpages/Mat/MatNullSpaceCreateRigidBody/__;!!G_uCfscf7eWS!eKqgIJjCdMzIU76f7X65AmGxrU_-lC7W02BMWafJ77DNf_IuQk6O1X3qU1x9Ez8NJ20vZEL-mF6T1yNmDnwv0eWa2w$>), >>> I see that I need to provide the coordinates of each node. I am using >>> staggered grid discretization. Do I need to provide coordinates of >>> staggered grid locations? >>> >>> Thanks, >>> -- >>> --Amneet >>> >>> >>> >>> -- --Amneet
