MG preconditioner issue

Matthew Knepley knepley at
Tue Mar 18 17:30:37 CDT 2008

On Tue, Mar 18, 2008 at 5:00 PM, Matt Funk <mafunk at> wrote:
> Hi,
>  i am trying out the MG preconditioner in PETSc and am encountering some
>  issues. In fact when i use the MG preconditioner i get a segmentation
>  violation. This does not happen with other preconditioners.

If you just do something like -pc_type mg, then you will definitely
get an error.
PC_MG is just the skeleton for a multigrid preconditioner. MG relies
on knowledge
of both the operator and domain, which is in general not available to PETSc.

If you want something that just works, I suggest configuring with --download-ml
or --download-hypre or --download-prometheus and running with the AMG
provided in those packages.

If you are using a DA, then you can use DMMG which provides the extra


>  Running Petsc in debug mode with the -info option did not seem to produce any
>  useful data (at least to me)
>  I thought i'd ask if someone encountered this before i use valgrind. I am
>  using 2.3.3-p8. Or does anyone have a hint on where i could start looking?
>  Again, what bothers me is that the other preconditioner do not throw any sort
>  of error.
>  thanks
>  mat

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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