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

[Garth N. Wells]

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