[petsc-users] How rto use multigrid?

[Matthew Knepley]

On Sun, Oct 28, 2012 at 9:38 AM, w_ang_temp <w_ang_temp at 163.com> wrote:

> Hello, Jed
>     Thanks for your timely reply. I deal with the soil-water coupled
> problem in geotechnical engineering,
> whose stiffness matrix is ill-conditioned. I have did some work about it,
> mainly finding the effective
> solvers and preconditioners. I used the command line option like this:
> mpiexec -n 4 ./ex4f -ksp_type cgs -pc_type sor -ksp_rtol 1.0e-15
> -ksp_converged_reason.
>

If SOR works as a preconditioner, then definitely use AMG as Jed suggested.
It is almost certain to work.

   Matt


>     So, I also want to use the multigrid just like the simple command.
> There is only a little introduction
> about multigrid in the manual. Multigrid is complex and not a easy thing
> for me, so I just need to konw how
> to use it simply in PETSc to solve the Ax=b system.
>     Thanks.
>                                                                Jim
>
>
>
>
>
> >At 2012-10-28 21:17:00,"Jed Brown" <jedbrown at mcs.anl.gov> wrote:
>
> >Algebraic multigrid can be used directly, -pc_type gamg
> -pc_gamg_agg_nsmooths 1. Geometric either required that you use the PCMG
> interface to set >interpolation (and provide a coarse operator for
> non-Galerkin) or use a DM that provides coarsening capability.
>
> >What kind of problem are you solving?
> >>On Oct 28, 2012 6:09 AM, "w_ang_temp" <w_ang_temp at 163.com> wrote:
>
>>  >>Hello,
>> >>   I want to use the multigrid as a preconditioner. The introduction
>> about it in the manual is little.
>> >>So are there some typical examples or details about multigrid? Is it
>> used just like other preconditioners
>> >>like jacobi, sor, which can be simply used in the cammand line options?
>> >>   Thanks.
>> >>
>> Jim
>>
>>
>>
>
>


-- 
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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