[petsc-users] mg pre-conditioner default setup from PETSc-3.4 to PETSc-3.7

[Hong]

Federico :

>
>   Coarse grid solver -- level -------------------------------
>     KSP Object:    (mg_levels_0_)     128 MPI processes
>       type: chebyshev
>         Chebyshev: eigenvalue estimates:  min = 0.223549, max = 2.45903
>         Chebyshev: eigenvalues estimated using gmres with translations
>  [0. 0.1; 0. 1.1]
>         KSP Object:        (mg_levels_0_esteig_)         128 MPI processes
>           type: gmres
>             GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
> Orthogonalization with no iterative refinement
>             GMRES: happy breakdown tolerance 1e-30
>           maximum iterations=10, initial guess is zero
>           *tolerances:  relative=1e-12*, absolute=1e-50, divergence=10000.
>           left preconditioning
>           *using PRECONDITIONED norm type for convergence test*
>       maximum iterations=2, initial guess is zero
>       tolerances:  relative=1e-05, absolute=1e-50, divergence=10000.
>       left preconditioning
>       using NONE norm type for convergence test
>

Chebyshev requires an estimate of operator eigenvalues, for which we use
few gmres iterations. These default options are used for eigenvalue
estimates.

Hong
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