[petsc-users] Is PCMG a generic PC object ?

[Matthew Knepley]

On Fri, Dec 3, 2010 at 12:33 PM, Randall Mackie <rlmackie862 at gmail.com>wrote:

> Are there any examples that show how to use the ML PC?
>

-pc_type ml

It is Algebraic Multigrid.

   Matt


> Randy
>
>
> On Dec 3, 2010, at 9:02 AM, Matthew Knepley wrote:
>
> I will also note that a good intro for implementing your own might be the
> ML PC
> in Petsc. It puts the ML AMG package into the PCMG framework.
>
>    Matt
>
> On Fri, Dec 3, 2010 at 3:44 AM, Dave May <dave.mayhem23 at gmail.com> wrote:
>
>> Hey Vijay,
>>  PCMG is generic. If you provide the operators for each level, along
>> with the restriction and prolongation,
>> you can use PCMG. It doesn't need to know about the mesh.
>>
>> You don't actually need to provide the coarse grid operators.
>> Given the fine grid operator and R and optionally P, you can use
>> Galerkin coarsening by calling
>> PCMGSetGalerkin() or via the command line arg -pc_mg_galerkin
>> Also, if you don't specify the prolongation, petsc will use P = R^T.
>>
>>
>> Cheers,
>>   Dave
>>
>>
>> On 3 December 2010 06:02, Vijay S. Mahadevan <vijay.m at gmail.com> wrote:
>> > Hi all,
>> >
>> > I was wondering whether the MG preconditioner object is generic enough
>> > to work out of the box like say ILU or SOR.  To elaborate on this, if
>> > I can provide the number of levels, restriction and prolongation
>> > operators for each level and the system operators along with vectors
>> > allocated for solution and rhs, would it work as a preconditioner for
>> > my given problem and a prescribed rhs at the finest level of PCMG. Or
>> > does it need some knowledge of the fine and coarser meshes to perform
>> > the MG operations correctly ?
>> >
>> > All the examples I've seen using MG in petsc involve the DA and DMMG
>> > objects and since I use my own mesh and corresponding discretization
>> > code for an elliptic system, I'm curious about this usage. It would
>> > not be terribly difficult to write my own framework to do a simple
>> > V-cycle with my existing framework but since petsc already provides
>> > this functionality along with different types of MG solves (with
>> > verified code!), I really want to use it for my system. Any help
>> > and/or pointers are welcome.
>> >
>> > Thanks,
>> > vijay
>> >
>>
>
>
>
> --
> 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
>
>
>


-- 
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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