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

[Matthew Knepley]

On Thu, Jan 23, 2014 at 9:02 AM, Dave May <dave.mayhem23 at gmail.com> wrote:

> It should be just "est".
>

I cannot explain


https://bitbucket.org/petsc/petsc/src/82b87d87c781ccd50dbcf95f010f70771da1bbfc/src/ksp/ksp/impls/specest/specest.c?at=master#cl-130

or


https://bitbucket.org/petsc/petsc/src/82b87d87c781ccd50dbcf95f010f70771da1bbfc/src/ksp/ksp/impls/specest/specest.c?at=master#cl-175

     Matt


> However, I misspelled "cheby". Those options should be
>
> -mg_levels_ksp_type chebyshev
> -mg_levels_ksp_chebyshev_estimate_eigenvalues 0,0.2,0,1.1
>
>
>
>
>
>
> On 23 January 2014 15:56, Matthew Knepley <knepley at gmail.com> wrote:
>
>> 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
>>
>
>


-- 
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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