@Barry, Upon your suggestion, I added -pc_fieldsplit_detect_saddle_point to my previously used command line options. But, I get the same error message as earlier.
------------------------------------------- Regards Sthavishtha On Mon, Apr 12, 2021 at 4:36 AM Barry Smith <[email protected]> wrote: > > 0 SNES Function norm 6.145506780035e-04 > 0 KSP Residual norm 2.013603254316e+41 > > My guess is that your matrix has zeros or essentially zeros on some > diagonal entries, this could be breaking > > Relax down symmetric-SOR/Jacobi > Relax up symmetric-SOR/Jacobi > > since the smoother would be dividing by those numbers. Standard multigrid > methods generally cannot handle such matrices without adjustments. > > On approach for such problems is to use PCFIELDSPLIT and split off the > zero diagonal portion while using AMG on the > rest -pc_fieldsplit_detect_saddle_point > see PCFieldSplitSetDetectSaddlePoint(). > > Barry > > > > > On Apr 11, 2021, at 1:06 PM, Matthew Knepley <[email protected]> wrote: > > On Sun, Apr 11, 2021 at 1:37 PM sthavishtha bhopalam < > [email protected]> wrote: > >> Hello PETSc users >> >> I am trying to experiment with Hypre's BoomerAMG preconditioner which >> continually yields the error message "Linear solve did not converge due to >> DIVERGED_DTOL iterations 1". I would appreciate if someone can suggest some >> ways I could get BoomerAMG to yield converged results - the attached output >> shows a snippet of the error message. *Command Line options I used for >> BoomerAMG* : *-pc_type hypre -pc_hypre_type boomeramg >> -pchypreboomeramgtol 1.0e-3 -pchypreboomeramgstrongthreshold 0.25 -ksp_type >> richardson -pc_hypre_boomeramg_max_iter 6 -snes_rtol 1.0e-3 -ksp_rtol >> 1.0e-3 -ksp_view -snes_view -ksp_monitor -snes_monitor -ksp_max_it 100 >> -ksp_converged_reason -snes_converged_reason* >> >> I also tried using *-ksp_type gmres*, different values of >> *-pc_hypre_boomeramg_max_iter*, *-pchypreboomeramgstrongthreshold*, >> *-ksp_initial_guess_nonzero* but all yielded the same error message. >> >> However, the direct solver converges as required - the attached output >> shows a snippet of the norms from the SNES and KSP. >> *Command Line options I used for the direct solver* : *-ksp_type gmres >> -pc_type lu -pc_factor_shift_type nonzero -pc_factor_mat_solver_type mumps >> -snes_converged_reason -ksp_converged_reason -ksp_rtol 1e-3 -snes_rtol 1e-3 >> -ksp_monitor -snes_monitor* >> >> There is no particular reason for using the AMG here, but I just wanted >> to familiarize with it's options to see which of them need to be >> particularly tuned to yield converged and correct results. >> > > Hypre is only going to work for a very specific set of systems. What are > you solving? > > Thanks, > > Matt > > >> Thanks >> ------------------------------------------- >> Regards >> >> Sthavishtha >> >> >> >> >> > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/~knepley/> > > >
