[petsc-users] Set PC PythonContext within NPC
Asbjørn Nilsen Riseth
riseth at maths.ox.ac.uk
Wed Jul 1 08:21:15 CDT 2015
fixed my issue by calling snes.setUp(), so I can access the linear PC from
This requires pull request 339:
At some point I'll learn to use app contexts in my python shells. For now,
I'm using _init_() to store any application-specific values in my class.
On Thu, 25 Jun 2015 at 22:17 Lawrence Mitchell <
lawrence.mitchell at imperial.ac.uk> wrote:
> > On 24 Jun 2015, at 17:02, Asbjørn Nilsen Riseth <riseth at maths.ox.ac.uk>
> > Hi all,
> > I'm currently trying to set up a nonlinear solver that uses NGMRES with
> NEWTONLS as a right preconditioner. The NEWTONLS has a custom linear
> preconditioner. Everything is accessed through petsc4py.
> > *Is there a way I can configure a NPC NEWTONLS KSP CompositePC without
> first calling solve on my outer snes?*
> > My NEWTONLS has the following KSP setup:
> > FGMRES
> > | PCCOMPOSITE
> > || PYTHON
> > || ILU
> > The way I understand things, the NPC is not created/set up until
> SNESSolve_NGMRES() is called. Therefore, I cannot call
> snes.getNPC().ksp.pc.getCompositePC(0).setPythonContext(ctx) before I have
> called snes.solve().
> > What I currently do is a try/except on snes.solve to create/set up the
> pccomposite. Then I can set my pythoncontext and it runs fine. This is
> quite ugly though, so I was hoping anyone would have a better approach.
> I think you can do the following:
> Define a class in some module:
> # (in module foo)
> class MyPC(object):
> def setUp(self, pc):
> # do any setup here.
> def apply(self, pc, x, y):
> # apply preconditioner
> And pass:
> -npc_sub_1_pc_type python -npc_sub_1_pc_python_context foo.MyPC
> You can pull the app context out in the class's setUp method by doing:
> ctx = pc.getDM().getAppCtx()
> Assuming that you're running with a branch that contains
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the petsc-users