[petsc-users] Command line option to set number iterations for Chebyshev eigenvalue estimation?

[Dave May]

If you don't have any prefix set on the outer KSP, you should be able to
simply do

-mg_levels_ksp_type chebychev
-mg_levels_ksp_chebychev_estimate_eigenvalues 0,0.2,0,1.1
-mg_levels_est_ksp_type cg
-mg_levels_est_ksp_max_it X

Cheers,
  Dave





On 23 January 2014 15:49, Garth N. Wells <gnw20 at cam.ac.uk> wrote:

> On 2014-01-23 14:32, Matthew Knepley wrote:
>
>> On Thu, Jan 23, 2014 at 5:35 AM, Garth N. Wells <gnw20 at cam.ac.uk>
>> wrote:
>>
>>  Is there are command line option to set the number of iterations
>>> used for the eigenvalue estimation inside the Chebyshev
>>> preconditioner?  "-gamg_est_ksp_max_it" does the trick with GAMG,
>>> but I'd also like to change the number of iterations when using
>>> Chebyshev smoothing with ML.
>>>
>>
>> In GAMG, we use PETSc itself to do the estimate, and give it the
>> prefix gamg_est_. In ML, as far as I can see from the code, we use the
>> internal
>> estimator, and I don't think they give us this knob.
>>
>>
> I'm not so interested in the what happens inside ML, but the Chebyshev
> smoother that PETSc applies. With the default 10 GMRES iterations, the
> eigenvalue estimate is not good enough for my problem, which leads to the
> outer CG breaking down with an indefinite operator error.
>
> I can get it working by changing
>
>   -mg_levels_ksp_chebyshev_estimate_eigenvalues
>
> but I'd rather do a few more iterations to get a better eigenvalue
> estimate. It would also be nice to be able to switch from GMRES to CG. I
> can do this with GAMG via "-gamg_est_ksp_type"
>
> Garth
>
>
>     Matt
>>
>>
>>  Garth
>>>
>>
>> --
>> 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
>>
>
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