Dave,
I am using a 2D decomposition, so if I increase the number of levels, I
have to decrease the number of processors I am using
in order to have enough grid points per processor for the multigrid to work.
Michele
On 10/02/2013 03:05 PM, Dave May wrote:
And why are you fixed on 5 levels?
On Wednesday, 2 October 2013, Barry Smith wrote:
Something is wrong, you should be getting better convergence.
Please answer my other email.
On Oct 2, 2013, at 1:10 PM, Michele Rosso <[email protected]
<javascript:;>> wrote:
> Thank you all for your contribution.
> So far the fastest solution is still the initial one proposed by
Jed in an earlier round:
>
> -ksp_atol 1e-9 -ksp_monitor_true_residual -ksp_view
-log_summary -mg_coarse_pc_factor_mat_solver_package superlu_dist
> -mg_coarse_pc_type lu -mg_levels_ksp_max_it 3
-mg_levels_ksp_type richardson -options_left -pc_mg_galerkin
> -pc_mg_levels 5 -pc_mg_log -pc_type mg
>
> where I used -mg_levels_ksp_max_it 3 as Barry suggested
instead of -mg_levels_ksp_max_it 1.
> I attached the diagnostics for this case. Any further idea?
> Thank you,
>
> Michele
>
>
> On 10/01/2013 11:44 PM, Barry Smith wrote:
>> On Oct 2, 2013, at 12:28 AM, Jed Brown <[email protected]
<javascript:;>> wrote:
>>
>>> "Mark F. Adams" <[email protected] <javascript:;>> writes:
>>>> run3.txt uses:
>>>>
>>>> -ksp_type richardson
>>>>
>>>> This is bad and I doubt anyone recommended it intentionally.
>> Hell this is normal multigrid without a Krylov accelerator.
Under normal circumstances with geometric multigrid this should be
fine, often the best choice.
>>
>>> I would have expected FGMRES, but Barry likes Krylov smoothers and
>>> Richardson is one of a few methods that can tolerate nonlinear
>>> preconditioners.
>>>
>>>> You also have, in this file,
>>>>
>>>> -mg_levels_ksp_type gmres
>>>>
>>>> did you or the recommenders mean
>>>>
>>>> -mg_levels_ksp_type richardson ???
>>>>
>>>> you are using gmres here, which forces you to use fgmres in
the outer solver. This is a safe thing to use you if you apply
your BCa symmetrically with a low order discretization then
>>>>
>>>> -ksp_type cg
>>>> -mg_levels_ksp_type richardson
>>>> -mg_levels_pc_type sor
>>>>
>>>> is what I'd recommend.
>>> I thought that was tried in an earlier round.
>>>
>>> I don't understand why SOR preconditioning in the Krylov
smoother is so
>>> drastically more expensive than BJacobi/ILU and why SOR is
called so
>>> many more times even though the number of outer iterations
>>>
>>> bjacobi: PCApply 322 1.0 4.1021e+01 1.0 6.44e+09
1.0 3.0e+07 1.6e+03 4.5e+04 74 86 98 88 92 28160064317351226 20106
>>> bjacobi: KSPSolve 46 1.0 4.6268e+01 1.0 7.52e+09
1.0 3.0e+07 1.8e+03 4.8e+04 83100100 99 99 31670065158291309 20800
>>>
>>> sor: PCApply 1132 1.0 1.5532e+02 1.0 2.30e+10
1.0 1.0e+08 1.6e+03 1.6e+05 69 88 99 88 93 21871774317301274 18987
>>> sor: KSPSolve 201 1.0 1.7101e+02 1.0 2.63e+10
1.0 1.1e+08 1.8e+03 1.7e+05 75100100 99 98 24081775248221352 19652
>>
>
> <best.txt>
