[petsc-users] How rto use multigrid?

[w_ang_temp]

Thanks. I will have a try.
 
                                Jim







在 2012-10-28 21:46:23，"Matthew Knepley" <knepley at gmail.com> 写道：
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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