[petsc-users] Setting up nonlinear preconditioning with petsc4py

[Blauth, Sebastian]

Hi everyone,

 

I wanted to try nonlinear preconditioning for solving nonlinear systems. The
problems arise from PDEs discretized with FEniCS and I have successfully
implemented a wrapper for SNES. However, once I want to try nonlinear
preconditioning by adding the option “-npc_snes_type newtonls” (or other
solvers such as nrichardson), I get the error code 56.

 

My approach looks something like this

 

from petsc4py import PETSc

 

snes = PETSc.SNES().create()

snes.setFunction(self.assemble_function, self.residual_petsc)

snes.setJacobian(self.assemble_jacobian, self.A_petsc, self.P_petsc)

snes.setFromOptions()

 

snes.solve(None, self.u.vector().vec())

snes.destroy()

 

I don’t think that my user defined functions are problematic. The code runs
well with the options (just an example)

-snes_type newtonls

-snes_rtol 1e-6

-snes_monitor

-ksp_type gmres

-ksp_monitor_true_residual

-pc_type lu

-pc_factor_mat_solver_type mumps

-mat_mumps_icntl_24

 

Here, the gmres is just used to verify that the direct solver works as
expected. Newton Krylov methods also work well.

However, once I use

 

-snes_type nrichardson

-npc_snes_type newtonls

-npc_snes_max_it 4

 

(as discussed e.g. in
https://climatemodeling.org/~rmills/talks/PSU-ACM-seminar-2024.pdf) I get
the error message

 

File "/p/tv/blauths/cashocs/cashocs/nonlinear_solvers/snes.py", line 250, in
solve

    snes.solve(None, self.u.vector().vec())

  File "petsc4py/PETSc/SNES.pyx", line 1555, in petsc4py.PETSc.SNES.solve

petsc4py.PETSc.Error: error code 56

 

I would be really grateful if someone could point me to the right direction
on how to use nonlinear precondition with petsc4py.

Thanks a lot in advance,

Sebastian

 

--

Dr. Sebastian Blauth

Fraunhofer-Institut für

Techno- und Wirtschaftsmathematik ITWM

Abteilung Transportvorgänge

Fraunhofer-Platz 1, 67663 Kaiserslautern

Telefon: +49 631 31600-4968

 <mailto:sebastian.blauth at itwm.fraunhofer.de>
sebastian.blauth at itwm.fraunhofer.de

 <https://www.itwm.fraunhofer.de> https://www.itwm.fraunhofer.de

 

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