Sure, I can even share the relevant parts of the code as this is part of my project cashocs. The related PR can be found here: https://github.com/sblauth/cashocs/pull/530
The relevant part of the SNES solver setup with FEniCS is here: https://github.com/sblauth/cashocs/blob/main/cashocs/nonlinear_solvers/snes.py#L235 There, I realized that FEniCS by default generates empty matrices and vectors which will have the correct size and sparsity pattern only after they have been assembled at least once. But I noticed that if I did only assemble them during the call to snes.solve, then, e.g., using MUMPS as solver caused issues. If I preassemble the matrices, everything works fine. And the same goes for the residual, which is what caused the issues with the nonlinear preconditioning. Best, Sebastian -- Dr. Sebastian Blauth Fraunhofer-Institut für Techno- und Wirtschaftsmathematik ITWM Abteilung Transportvorgänge Fraunhofer-Platz 1, 67663 Kaiserslautern Telefon: +49 631 31600-4968 sebastian.bla...@itwm.fraunhofer.de <mailto:sebastian.bla...@itwm.fraunhofer.de> https://www.itwm.fraunhofer.de From: Matthew Knepley <knep...@gmail.com> Sent: Wednesday, December 4, 2024 3:51 PM To: Blauth, Sebastian <sebastian.bla...@itwm.fraunhofer.de> Cc: Stefano Zampini <stefano.zamp...@gmail.com>; PETSc users list <petsc-users@mcs.anl.gov> Subject: Re: [petsc-users] Setting up nonlinear preconditioning with petsc4py On Wed, Dec 4, 2024 at 8:09 AM Blauth, Sebastian <sebastian.bla...@itwm.fraunhofer.de <mailto:sebastian.bla...@itwm.fraunhofer.de> > wrote: Thanks a lot for the hint. With this I could find the error myself: I had not initialized the residual vector correctly, which has to be duplicated, hence the error. Assembling this once with FEniCS fixed the error and I can now use nonlinear preconditioning. Thanks a lot! I would be very interested to hear how it works if you have the time to mail us back. Thanks Matt Best, Sebastian -- Dr. Sebastian Blauth Fraunhofer-Institut für Techno- und Wirtschaftsmathematik ITWM Abteilung Transportvorgänge Fraunhofer-Platz 1, 67663 Kaiserslautern Telefon: +49 631 31600-4968 sebastian.bla...@itwm.fraunhofer.de <mailto:sebastian.bla...@itwm.fraunhofer.de> https://www.itwm.fraunhofer.de From: Stefano Zampini <stefano.zamp...@gmail.com <mailto:stefano.zamp...@gmail.com> > Sent: Wednesday, December 4, 2024 1:56 PM To: Matthew Knepley <knep...@gmail.com <mailto:knep...@gmail.com> > Cc: Blauth, Sebastian <sebastian.bla...@itwm.fraunhofer.de <mailto:sebastian.bla...@itwm.fraunhofer.de> >; PETSc users list <petsc-users@mcs.anl.gov <mailto:petsc-users@mcs.anl.gov> > Subject: Re: [petsc-users] Setting up nonlinear preconditioning with petsc4py FENICS swallows any useful error information returned from PETSc. You can try using the below code snippet at the beginning of your script right after you loaded dolfin stuff PETSc.Sys.pushErrorHandler('python') On Wed, Dec 4, 2024, 15:48 Matthew Knepley <knep...@gmail.com <mailto:knep...@gmail.com> > wrote: On Wed, Dec 4, 2024 at 4:44 AM Blauth, Sebastian <sebastian.bla...@itwm.fraunhofer.de <mailto:sebastian.bla...@itwm.fraunhofer.de> > wrote: 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 <https://urldefense.us/v3/__https:/climatemodeling.org/*rmills/talks/PSU-ACM-seminar-2024.pdf__;fg!!G_uCfscf7eWS!ZpQxakVxVcyih0WUbW_MxFNHXR0tUbZAvis8z497q782yqbJraYBBCMst79xJm6nlGdBUqW3I2vIDAtJiUTR$> ) I get the error message File "/p/tv/blauths/cashocs/cashocs/nonlinear_solvers/snes.py", line 250, in solve snes.solve(None, self.u.vector().vec()) File "petsc4py/PETSc/SNES.pyx", line 1555, in petsc4py.PETSc.SNES.solve petsc4py.PETSc.Error: error code 56 I would be really grateful if someone could point me to the right direction on how to use nonlinear precondition with petsc4py. 56 is PETSC_ERR_SUP, which means we hit an unsupported operation. petsc4py preserves the stack trace, so FEniCS should not be throwing it away (along with the error message). Maybe run in the debugger so we can see the error message and stack? Thanks, Matt Thanks a lot in advance, Sebastian -- Dr. Sebastian Blauth Fraunhofer-Institut für Techno- und Wirtschaftsmathematik ITWM Abteilung Transportvorgänge Fraunhofer-Platz 1, 67663 Kaiserslautern <https://www.google.com/maps/search/Fraunhofer-Platz+1,+67663+Kaiserslautern?entry=gmail&source=g> Telefon: +49 631 31600-4968 sebastian.bla...@itwm.fraunhofer.de <mailto:sebastian.bla...@itwm.fraunhofer.de> https://www.itwm.fraunhofer.de <https://urldefense.us/v3/__https:/www.itwm.fraunhofer.de__;!!G_uCfscf7eWS!ZpQxakVxVcyih0WUbW_MxFNHXR0tUbZAvis8z497q782yqbJraYBBCMst79xJm6nlGdBUqW3I2vIDJ9nKGZK$> -- 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 https://www.cse.buffalo.edu/~knepley/ <https://urldefense.us/v3/__http:/www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!ZpQxakVxVcyih0WUbW_MxFNHXR0tUbZAvis8z497q782yqbJraYBBCMst79xJm6nlGdBUqW3I2vIDIJYMNfe$> -- 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 https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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