[petsc-dev] question about linear solver examples in petsc

Matthew Knepley knepley at mcs.anl.gov
Fri Dec 5 11:31:25 CST 2014

On Thu, Dec 4, 2014 at 1:00 PM, Raphaël Couturier <
raphael.couturier at univ-fcomte.fr> wrote:

> Hello Matt,
> Thank you for all your work on PETSc.
> I would like to know if you or your colleagues have some examples of code
> with linear systems in PETSc that are difficult to solve with more of less
> all preconditioners and GMRES?

I am Cc'ing petsc-dev since better feedback might come from there. ex15 is
the p-Laplacian, ex16
is large deformation elasticity (ex54 is infinitesimal). These are somewhat
difficult, but most of the
difficulty is getting MG to work right. These are likely candidates to be
solved with FMG, neglecting

In the past, hard things to solve have generally been very non-normal
matrices. We do not maintain
a catalogue since we (I at least) have almost given up on black box solvers
in favor of focusing
on preconditioners for certain problem types. However, other people on here
might have specific
problems that they need solved.



> In fact, I am working on a new method which solves, for example ex15 or
> ex54 of ksp/ksp/examples/tutorials with large instances (for example
> 200,000,000 components or more) with the mg preconditioner and for example
> 8192 cores, faster than GMRES.
> So I would like to know if it is possible to test other difficult examples?
> I have submitted my work to a conference, and as soon as this work is
> accepted, I will be able to give more details on the method.
> Best wishes,
> Raphaël Couturier
> http://members.femto-st.fr/raphael-couturier/

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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