[petsc-users] Preconditioning systems of equations with complex numbers

[Jed Brown]

Matthew Knepley via petsc-users <petsc-users at mcs.anl.gov> writes:

>> 2) I tried all the suggestions mentioned before: setting
>> -pc_gamg_agg_nsmooths 0  -pc_gamg_square_graph 10 did not improve my
>> convergence. Neither did explicitly setting -mg_coarse_pc_type lu or more
>> iterations of richardson/sor.
>>
>
> 1) Can we see some convergence for these? LU HAS to be better than the
> alternative, but you are saying that convergence still
> stalls above that I think. Okay, but I do not understand how SOR was
> working on the smaller problem, and cannot solve the coarse
> problem. However, it could be if the interpolation is crap, which it sounds
> like is true here.
>
> Jed, does that makes sense? If so, I would think about doing some bootstrap
> stuff.

Justin, can you compute and plot the spectrum of a small problem (<1000
dofs) as well as the eigenvectors of the extremal eigenvalues?