[petsc-users] How to use multigrid?

[w_ang_temp]

Hello, Matthew
 
        I just mean that the problem that I am resolving is a finite element problem. The linear system of it  is true elliptic equations.
I heared that AMG was an efficient solver, so I just want to have a try about AMG and find that if it is efficient.
       By the way, I want to confirm a conception. In my view, AMG itself can be a solver like gmres. It can also be used as a preconditioner
like jacobi and is used by combining with other solver. Is it right? If it is right, how use AMG solver?
 
        Thanks.
 
                                                                                                                        Jim




>在 2012-11-04 01:21:59，"Matthew Knepley" <knepley at gmail.com> 写道：
><On Sat, Nov 3, 2012 at 1:17 PM, w_ang_temp <w_ang_temp at 163.com> wrote:

>At 2012-11-04 01:08:26,"Jed Brown" <jedbrown at mcs.anl.gov> wrote:


>1. What kind of equation are you solving? AMG is not working well if it takes that many iterations.


>I just deal with the typical soil-water coupled geotechnical problems. It is a typical finite element equation. The matrix is 30000X30000 and ill-conditioned.



>We are now at the root of your problem. Solvers do not work on discretizations, they work on equations. No
>solver is designed for "finite elements", and there is no typical finite element problem.


>Multigrid works best on elliptic equations with smooth coefficients. Without that, you have to do special things.


>I can tell from the above discussion that you have not spent a lot of time researching successful preconditioning
>strategies for your problem in the literature. This is always the first step to building a high performance solver.


 > Thanks,


>     Matt
 

>2.



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>It is true a debugging version. And I used the same version dealing with the same problem, one preconditioner is asm
>and the other is amg. The time with amg is about 3 times as with asm. I do not know the reason. And I also do not know the
>meaning of '[0]PCSetData_AGG bs=1 MM=7601'.










--
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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