[petsc-users] How to use multigrid?

[Jed Brown]

On Sun, Nov 4, 2012 at 7:52 AM, Mark F. Adams <mark.adams at columbia.edu>wrote:

> 2) Try using hyper (-pc_type hyper -pc_hypre_type boomeramg).  Look at "PCApply
> 448", this should be like 10-20.  Configure your systems with
> --download-hyper=1 if you do not have it.
>

Jim, you can use -pc_type hypre (note the spelling "hypre", not "hyper").


>
> 3) Why do you say it is ill conditioned?  Stretched grids? large jumps in
> material coefficients?  Why do you think it is illoconditioned?
>

This question is important.

PETSc devs, we may need to write an FAQ about how saying that your problem
is "ill-conditioned" is useless, and explaining the sort of context that is
necessary to say something useful.
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