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

[Matthew Knepley]

On Thu, Jan 23, 2014 at 8:54 AM, Dave May <dave.mayhem23 at gmail.com> wrote:

> 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
>

Are you sure the est_ is not specest_?

  Thanks,

     Matt


> 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
>>>
>>
>


-- 
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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