[petsc-users] Setting up nonlinear preconditioning with petsc4py

[Matthew Knepley]

On Wed, Dec 4, 2024 at 8:09 AM Blauth, Sebastian <
sebastian.blauth at 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.blauth at itwm.fraunhofer.de
>
> https://urldefense.us/v3/__https://www.itwm.fraunhofer.de__;!!G_uCfscf7eWS!apTDPPZWCcPl0SpwhG_O2c_qShB9EsoiAl8XyoHxoNowvDTMyo8-w17OoKH1i5zqmYbvLI9l0EMpe17p3IXT$ 
>
>
>
> *From:* Stefano Zampini <stefano.zampini at gmail.com>
> *Sent:* Wednesday, December 4, 2024 1:56 PM
> *To:* Matthew Knepley <knepley at gmail.com>
> *Cc:* Blauth, Sebastian <sebastian.blauth at itwm.fraunhofer.de>; PETSc
> users list <petsc-users at 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 <knepley at gmail.com> wrote:
>
> On Wed, Dec 4, 2024 at 4:44 AM Blauth, Sebastian <
> sebastian.blauth at 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://urldefense.us/v3/__https://climatemodeling.org/*rmills/talks/PSU-ACM-seminar-2024.pdf__;fg!!G_uCfscf7eWS!apTDPPZWCcPl0SpwhG_O2c_qShB9EsoiAl8XyoHxoNowvDTMyo8-w17OoKH1i5zqmYbvLI9l0EMpe83o8hLf$ 
> <https://urldefense.us/v3/__https:/climatemodeling.org/*rmills/talks/PSU-ACM-seminar-2024.pdf__;fg!!G_uCfscf7eWS!ZpQxakVxVcyih0WUbW_MxFNHXR0tUbZAvis8z497q782yqbJraYBBCMst79xJm6nlGdBUqW3I2vIDAtJiUTR$>)
> I get the error message
>
>
>
> File "/p/tv/blauths/cashocs/cashocs/nonlinear_solvers/snes.py", line 250,
> in solve
>
>     snes.solve(None, self.u.vector().vec())
>
>   File "petsc4py/PETSc/SNES.pyx", line 1555, in petsc4py.PETSc.SNES.solve
>
> petsc4py.PETSc.Error: error code 56
>
>
>
> I would be really grateful if someone could point me to the right
> direction on how to use nonlinear precondition with petsc4py.
>
>
>
> 56 is PETSC_ERR_SUP, which means we hit an unsupported operation. petsc4py
> preserves the stack trace, so FEniCS should not be throwing it away (along
> with the error message). Maybe run in the debugger so we can see the error
> message and stack?
>
>
>
>   Thanks,
>
>
>
>       Matt
>
>
>
> Thanks a lot in advance,
>
> Sebastian
>
>
>
> --
>
> Dr. Sebastian Blauth
>
> Fraunhofer-Institut für
>
> Techno- und Wirtschaftsmathematik ITWM
>
> Abteilung Transportvorgänge
>
> Fraunhofer-Platz 1, 67663 Kaiserslautern
> <https://urldefense.us/v3/__https://www.google.com/maps/search/Fraunhofer-Platz*1,*67663*Kaiserslautern?entry=gmail&source=g__;Kysr!!G_uCfscf7eWS!apTDPPZWCcPl0SpwhG_O2c_qShB9EsoiAl8XyoHxoNowvDTMyo8-w17OoKH1i5zqmYbvLI9l0EMpe-CZb10E$ >
>
> Telefon: +49 631 31600-4968
>
> sebastian.blauth at itwm.fraunhofer.de
>
> https://urldefense.us/v3/__https://www.itwm.fraunhofer.de__;!!G_uCfscf7eWS!apTDPPZWCcPl0SpwhG_O2c_qShB9EsoiAl8XyoHxoNowvDTMyo8-w17OoKH1i5zqmYbvLI9l0EMpe17p3IXT$ 
> <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
>
>
>
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>
>

-- 
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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