[petsc-users] Boomeramg as a solver

[jibum kim]

Are you saying that boomeramg with richardson iterations is same as the 
multigrid without a preconditioner? and if it the case, how can I set an 
extra preconditioner like ILU ?

Thanks,

- Jibum

----- Original Message ----- 
From: "Barry Smith" <bsmith at mcs.anl.gov>
To: "PETSc users list" <petsc-users at mcs.anl.gov>
Sent: Monday, November 01, 2010 2:25 PM
Subject: Re: [petsc-users] Boomeramg as a solver



On Nov 1, 2010, at 12:35 PM, jibum kim wrote:

> Hello,
>
> I've used  Boomeramg as a preconditioner.
>
> Now, I am wondering whether I can use Boomeramg as a solver ? and is it 
> possible that I use Boomeramg as both a preconditioner and a solver?
>
> I saw one slide saying that I can use KSPSetType(ksp, KSPRICHARDSON);
>
> But when I try it and use -ksp_view, it shows that my solver is Richardson 
> not  Boomeramg.
>
> Could u clarify this issue ?

  Richardson is our name for the iterative process   u^{n+1} = u^n + B(b - A 
u^n) for n=1,...max_it where B is the application of the preconditioner (in 
other words running a linear iterative method without any Krylov 
acceleration). In BoomerAMG's case B is one application of the V or W cycle 
(depending on your choice of BoomerAMG options).  So even though it says the 
"solver" is Richardson it is using BoomerAMG for the entire solution 
process, that is  algebraic multigrid with multiple V (or W cycles).

   Barry




>
> Thank you.
>
> - Jibum