On Nov 1, 2010, at 2:46 PM, jibum kim wrote:
> Are you saying that boomeramg with richardson iterations is same as the
> multigrid without a preconditioner?
I do not know what you mean by multigrid with or without a preconditioner?
Multigrid doesn't "take a preconditioner", it is an iterative solver that can
be used as a preconditioner but it cannot use other preconditioners.
> and if it the case, how can I set an extra preconditioner like ILU ?
What do you mean by an "extra preconditioner"? I assume you mean use ILU as
a smoother instead of SOR or Jacobi. BoomerAMG has no mechanism to use ILU as a
smoother so you cannot do this.
Because ML is more flexible it is possible to use PETSc's ILU as a smoother
for it.
Barry
>
> 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
>
>
