[petsc-users] BoomerAMG Hypre options

[sthavishtha bhopalam]

@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 <bsmith at petsc.dev> 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 <knepley at gmail.com> wrote:
>
> On Sun, Apr 11, 2021 at 1:37 PM sthavishtha bhopalam <
> sthavishthabr at 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
>> -------------------------------------------
>> 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/>
>
>
>
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