[petsc-users] Multigrid as preconditioner

[Barry Smith]

On Dec 14, 2011, at 7:07 AM, M.Younas wrote:

>  Hi, PETSc, Team,
> 
> I have solved a non-symmetric Poisson problem using GMRES(m) as solver and BoomerAMG (from Hypre) as preconditioner. But I don't understand how the BoomerAMG works as preconditioner with GMRES(m). Can anyone explain the procedure? Does it work like BoomerAMG precondition the liner system first (once only) and then GMRES(m) is being used for stopping criterion?

   By default PETSc uses ONE v-cycle of the BoomerAMG as a preconditioner for GMRES. 

   With the option -ksp_type richardson then PETSc is using a bunch of BoomerAMG v-cycles until the convergence criteria is satisfied without using a GMRES

   Barry

Note that a preconditioner can be any stationary linear iterative scheme. That is any linear operation that approximately solves A x = b, no matter how complicated the stationary linear iterative scheme is it can be used as a preconditioner.


> 
> Kind regards,
> 
> Younas
> 
> RUG, Groningen, The Netherlands.