[petsc-users] Multigrid

[Barry Smith]

On May 1, 2012, at 3:37 PM, Karthik Duraisamy wrote:

> Hello,
> 
>        I have been using PETSc for a couple of years with good success, but lately as my linear problems have become stiffer (condition numbers of the order of 1.e20), I am looking to use better preconditioners. I tried using PCMG with all the default options (i.e., I just specified my preconditioner as PCMG and did not add any options to it) and I am immediately seeing better convergence. 
> 
>        What I am not sure of is why? I would like to know more about the default parameters (the manual is not very explicit) and more importantly, want to know why it is working even when I haven't specified any grid levels and coarse grid operators. Any
> help in this regard will be appreciated.

   First run with -ksp_view to see what solver it is actually using.

   Barry

> 
>        Also, ultimately I want to use algebraic multigrid so is PCML a better option than BoomerAMG? I tried BoomerAMG with mixed results.
> 
> Thanks,
> Karthik
> 
> 
> 
> -- 
> 
> =======================================
> Karthik Duraisamy
> Assistant Professor (Consulting)
> Durand Building Rm 357
> Dept of Aeronautics and Astronautics
> Stanford University
> Stanford CA 94305
> 
> Phone: 650-721-2835
> Web:     www.stanford.edu/~dkarthik
> =======================================