BoomerAMG will never simply solve the resulting linear system. Mixing elliptic and hyperbolic equations into a linear system and then trying a "black-box" solver will never work.


On Apr 11, 2021, at 11:35 PM, sthavishtha bhopalam <sthavishthabr@gmail.com> wrote:

I am solving the isothermal form of the Navier-Korteweg system of equations - it's mixed hyperbolic-elliptic in nature.
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Regards

Sthavishtha Bhopalam Rajakumar






On Sun, Apr 11, 2021 at 11:37 PM Matthew Knepley <knepley@gmail.com> wrote:
On Sun, Apr 11, 2021 at 1:37 PM sthavishtha bhopalam <sthavishthabr@gmail.com> 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
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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