[petsc-users] AMG using ML : Advanced monitoring

[Matthew Knepley]

On Fri, May 11, 2012 at 4:47 PM, Karthik Duraisamy <dkarthik at stanford.edu>wrote:

> Dear all,
>
>      I have been able to use AMG (using ML) for some of my problems and am
> looking to delve deeper into the workings of the algorithm to better
> understand how to use it for larger and more complex problems. Since my
> problems are hyperbolic and involve sharp gradients, I think there is a
> possibility that coarse level operators are not very stable in some
> problems. I see evidence of this because in many cases, I need to use lu or
> a very high k ilu(k) on coarser levels to keep the iterative solver from
> diverging.
>
>    In this regard, I am wondering whether it is possible to obtain the
> coarse grid operators (or at the very least, the eigenstructure at these
> levels). Right now, I am doing the monitoring at the baseline level but I
> am looking for additional information.
>

You can get the smoother


http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/PC/PCMGGetSmoother.html

This has the operator, and you can use the Krylov eigen approximation. You
should have complete control.

    Matt


> Regards,
> 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
> =======================================
>



-- 
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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