On Fri, Aug 17, 2012 at 9:23 AM, Alexander Grayver <agrayver at gfz-potsdam.de>wrote:
> Right. > Could you please explain what do you mean by fragile? > Fragile means unreliable. The math is not right for Krylov methods in general. You are relying on side-effects of particular methods and preconditioner side combinations. Fragile is the opposite of "robust". For a "robust" method, you should start with a compatible discretization and/or choose a preconditioner that is stable on the quasi-null space and/or filter in a way that is consistent with the Krylov method (e.g. as described using FGMRES). > >> Looks a bit tricky. The number of fgmres iterations then defines number >> of the cycles correction will be applied, doesn't it? >> > > Yes. > > > If I do this command line only setup: > > -pc_type composite -pc_composite_type multiplicative -pc_composite_pcs > ksp,shell > > How does petsc know what ShellPCApply routine to take? I guess I have to > specify this in the code anyway? > Yeah, to select your preconditioner in this way, you should name it preconditioner something meaningful and use PCRegisterDynamic() just like the native implementations. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120817/4f1951da/attachment.html>
