> On Aug 11, 2016, at 4:42 PM, Ari Rappaport <[email protected]> wrote: > > Hi Guys, > So the algebraic multigrid works great for a Poisson equation. However, it's > choking on our Maxwell's Equations solver which is a form of curl/curl if I'm > not mistaken.
Maxwell's equations are tricky for multigrid. hypre has a solver specific for Maxwell's equation, you need to check it out; note this is not just running with hypre boomerAMG. If you run boomerAMG directly with Maxwell's you will not get satisfactory results. > I was going to give hypre AMS a try, but I'm having trouble installing it. > I'm getting the error "Downloaded hypre could not be used". Send configure.log > I'm using Ubuntu 14.04 if that makes a difference. Also, is non-algebraic > multigrid a reasonable choice for Maxwell's Equations? Even with geometric multigrid Maxwell's equations are nontrivial; you will need to do some literature search to determine how to handle the restriction/interpolation and smoothing to work well for Maxwell. Barry > > Thanks, > Ari > > ----- Original Message ----- > From: "Barry Smith" <[email protected]> > To: "Ari Rappaport" <[email protected]> > Cc: "Mark Adams" <[email protected]>, "For users of the development version of > PETSc" <[email protected]> > Sent: Wednesday, August 10, 2016 2:02:10 PM > Subject: Re: [petsc-dev] Algebraic Multigrid > > >> On Aug 10, 2016, at 2:52 PM, Ari Rappaport <[email protected]> wrote: >> >> Hi Mark, >> There was indeed a bug on our end. Now that we fixed it everything is >> working correctly even in parallel. I have one question still though. Is >> there a way to get the mg_levels_pc_type jacobi option >> set in the code without passing it as an argument to PetscInitialize? I'm >> using PCGAMGSetType(pc, PCJACOBI) but it doesn't seem to be working. > > You can call PetscOptionsSetValue("-<appropriate > prefix>_mg_levels_pc_type","jacobi") in the code anywhere before your code > creates the SNES or KSP object you are using. This is equivalent to putting > it on the command line. > > Barry > >> >> >> -Ari >> >> ----- Original Message ----- >> From: "Mark Adams" <[email protected]> >> To: "Ari Rappaport" <[email protected]> >> Cc: "For users of the development version of PETSc" <[email protected]> >> Sent: Wednesday, July 27, 2016 7:24:24 PM >> Subject: Re: [petsc-dev] Algebraic Multigrid >> >> There is clearly something very wrong with your code. I would suggest >> starting with an example code for instance KSP/examples/tutorial/ex56.c and >> incrementally add your operator to get something that is working. >> >> >> Also if you have multiple degrees of freedom per vertex, for instance >> elasticity, then you want to set the block size of the matrix accordingly. >> >> On Wednesday, July 27, 2016, Ari Rappaport < [email protected] > wrote: >> >> >> Hi Mark, >> We added the Jacobi line and it appears to accept that flag now. However, we >> are getting all zeros for the solution vector. And PETSc is claiming to have >> converged in 7 iterations to the relative tolerance. >> >> -Ari >> >> ----- Original Message ----- >> From: "Mark Adams" < [email protected] > >> To: "Ari Rappaport" < [email protected] >, "For users of the development >> version of PETSc" < [email protected] > >> Sent: Wednesday, July 27, 2016 3:26:03 PM >> Subject: Re: [petsc-dev] Algebraic Multigrid >> >> >> Please keep this on the Petsc list. >> >> We seem to have lost Jacobi smoother again. I'm suspecting that you're some >> funny character in your line with Jacobi that is Confusing the parser. Get >> back to the old file with the two two Jacobi entries and delete the other >> line and get Jacobi in the KSP view output. There should be no SOR in the >> output. >> >> >> On Wednesday, July 27, 2016, Ari Rappaport < [email protected] > wrote: >> >> >> Hi Mark, >> I added all these new things. The PCAMG is now ending very quickly but the >> residual is unreasonably large by about 10 orders of magnitude. I noticed >> the line "Linear solve did not converge due to DIVERGED_INDEFINITE_PC >> iterations 2" in the output, could this be causing the problem? It only >> appears to be going for 2 iterations now. >> >> -Ari >> >> ----- Original Message ----- >> From: "Mark Adams" < [email protected] > >> To: "Ari Rappaport" < [email protected] > >> Cc: "For users of the development version of PETSc" < [email protected] >> > >> Sent: Tuesday, July 26, 2016 5:07:34 PM >> Subject: Re: [petsc-dev] Algebraic Multigrid >> >> >> Ari, I would also check that your operator is not messed up in parallel. The >> solver is looking pretty solid. >> >> >> Also, you can configure PETSc with hypre and use '-pc_type hypre'. If hypre >> is also good in serial but hosed on multi-proc then it is most probably your >> operator. >> >> >> >> >> On Tue, Jul 26, 2016 at 6:58 PM, Mark Adams < [email protected] > wrote: >> >> >> >> So remove one of the -mg_levels_pc_type jacobi and add -mg_coarse_ksp_type >> preonly, then verify that this works on one proc and then try two procs. >> >> >> >> >> On Tue, Jul 26, 2016 at 6:56 PM, Mark Adams < [email protected] > wrote: >> >> >> >> Oh, actually this worked. You have this ...pc_type jacobi in there twice, so >> one of them was "unused". >> >> >> Try this with 2 processors now. >> >> >> >> >> On Tue, Jul 26, 2016 at 6:42 PM, Mark Adams < [email protected] > wrote: >> >> >> >> >> >> >> >> On Tue, Jul 26, 2016 at 6:24 PM, Ari Rappaport < [email protected] > wrote: >> >> >> So I commented out the line PCSetType(pc, PCGAMG). The line >> KSPSetFromOptions(ksp) was already in the code at the end of our >> initialization routine. I also added .petscrc to the working dir. Here is >> the current output. It seems as if Option left: name:-mg_levels_pc_type >> jacobi (no value) is still present in the output..I dunno. >> >> >> >> Yea, I dunno either. If you use -help you will get printout of the available >> options. If you do this you will see stuff like -mg_levels_1_ ... you can >> also see this in the ksp_view. There is a shortcut that lets you _not_ put >> "_1" in. Try putting this in for each level like so: >> >> >> >> -mg_levels_1_pc_type jacobi >> >> -mg_levels_2_pc_type jacobi >> -mg_levels_3_pc_type jacobi >> >> >> >> I also notice that the coarse grid ksp is GMRES. This is our fault. It >> should be preonly. Add: >> >> >> -mg_coarse_ksp_type preonly >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> -Ari >> >> ----- Original Message ----- >> From: "Mark Adams" < [email protected] > >> To: "Ari Rappaport" < [email protected] >, "For users of the development >> version of PETSc" < [email protected] > >> Sent: Tuesday, July 26, 2016 4:03:03 PM >> Subject: Re: [petsc-dev] Algebraic Multigrid >> >> >> >> >> At the end of this you have: >> >> >> >> #PETSc Option Table entries: >> -ksp_view >> -mg_levels_pc_type jacobi >> -options_left >> #End of PETSc Option Table entries >> There is one unused database option. It is: >> Option left: name:-mg_levels_pc_type jacobi (no value) >> >> >> So this jacobi parameter is not being used. >> >> >> Do you call KPSSetFromOptions? Do you set solver parameters in the code? >> Like PCGAMG? >> >> >> You should not set anything in the code, it just confuses things at this >> point. Use KSPSetFromOptions(). You can hardwire stuff before this call, >> this just lets you set the defaults, but you should always call this last to >> let command line parameters override the defaults. >> >> >> You can put this in a .petscrc file in the working directory and try again. >> >> >> >> -ksp_type cg >> -ksp_max_it 50 >> >> -ksp_rtol 1.e-6 >> -ksp_converged_reason >> -pc_type gamg >> -pc_gamg_type agg >> -pc_gamg_agg_nsmooths 1 >> -pc_gamg_coarse_eq_limit 10 >> -pc_gamg_reuse_interpolation true >> -pc_gamg_square_graph 1 >> -pc_gamg_threshold -0.05 >> -mg_levels_ksp_max_it 2 >> -mg_levels_ksp_type chebyshev >> -mg_levels_esteig_ksp_type cg >> -mg_levels_esteig_ksp_max_it 10 >> -mg_levels_ksp_chebyshev_esteig 0,.05,0,1.05 >> -mg_levels_pc_type jacobi >> -pc_hypre_type boomeramg >> -pc_hypre_boomeramg_no_CF >> -pc_hypre_boomeramg_agg_nl 1 >> -pc_hypre_boomeramg_coarsen_type HMIS >> -pc_hypre_boomeramg_interp_type ext+i >> >> >> >> >> >
