[petsc-users] KSP has an extra iteration when use shell matrix

Barry Smith bsmith at petsc.dev
Mon Feb 5 12:09:24 CST 2024 

  Send the entire code.


> On Feb 4, 2024, at 4:43 PM, Yi Hu <y.hu at mpie.de> wrote:
> 
> Thanks for your response. You are correct. I overlooked this step.
> 
> Now I am trying to correct my "shell matrix approach" for ex1f.F90 of snes solver (https://github.com/hyharry/small_petsc_test/blob/master/test_shell_jac/ex1f.F90). I realized that I need to record the base vector X in the context of shell matrix and then use this info to carry MyMult. However, the context cannot be obtained through MatShellGetContext(). Here are the critical parts of my code.
> 
>        INTERFACE MatCreateShell
>          SUBROUTINE MatCreateShell(comm,mloc,nloc,m,n,ctx,mat,ierr)
>            USE solver_context
>            MPI_Comm :: comm
>            PetscInt :: mloc,nloc,m,n
>            Vec :: ctx
>            Mat :: mat
>            PetscErrorCode :: ierr
>          END SUBROUTINE MatCreateShell
>        END INTERFACE MatCreateShell
> 
>        INTERFACE MatShellSetContext
>          SUBROUTINE MatShellSetContext(mat,ctx,ierr)
>            USE solver_context
>            Mat :: mat
>            !TYPE(MatCtx) :: ctx
>            Vec :: ctx
>            PetscErrorCode :: ierr
>          END SUBROUTINE MatShellSetContext
>        END INTERFACE MatShellSetContext
> 
>        INTERFACE MatShellGetContext
>          SUBROUTINE MatShellGetContext(mat,ctx,ierr)
>            USE solver_context
>            Mat :: mat
>            Vec, Pointer :: ctx
>            PetscErrorCode :: ierr
>          END SUBROUTINE MatShellGetContext
>        END INTERFACE MatShellGetContext
> 
> in my FormShellJacobian() I did
> 
> subroutine FormJacobianShell(snes,X,jac,B,dummy,ierr)
> 
> ......
> 
>   call MatShellSetContext(jac,X,ierr)
> 
> ......
> 
> Then in MyMult() I tried to recover this context by
> 
> call MatShellGetContext(J,x,ierr)
> 
> call VecView(x,PETSC_VIEWER_STDOUT_WORLD,ierr)
> 
> Then the program failed with
> 
> [0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> [0]PETSC ERROR: Null argument, when expecting valid pointer
> [0]PETSC ERROR: Null Pointer: Parameter # 1
> 
> In MyMult, I actually defined x to be a pointer. So I am confused here. 
> 
> Best regards,
> 
> Yi
> 
> On 1/31/24 03:18, Barry Smith wrote:
>> 
>>    It is not running an extra KSP iteration. This "extra" matmult is normal and occurs in many of the SNESLineSearchApply_* functions, for example, https://petsc.org/release/src/snes/linesearch/impls/bt/linesearchbt.c.html#SNESLineSearchApply_BT It is used to decide if the Newton step results in sufficient decrease of the function value.
>> 
>>   Barry
>> 
>> 
>> 
>>> On Jan 30, 2024, at 3:19 PM, Yi Hu <y.hu at mpie.de> <mailto:y.hu at mpie.de> wrote:
>>> 
>>> Hello Barry,
>>> 
>>> Thanks for your reply. The monitor options are fine. I actually meant my modification of snes tutorial ex1f.F90 does not work and has some unexpected behavior. I basically wanted to test if I can use a shell matrix as my jacobian (code is here https://github.com/hyharry/small_petsc_test/blob/master/test_shell_jac/ex1f.F90). After compile my modified version and run with these monitor options, it gives me the following,
>>> 
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   0 SNES Function norm 6.041522986797e+00 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 6.041522986797e+00 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 5.065392549852e-16 
>>>   Linear solve converged due to CONVERGED_RTOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   1 SNES Function norm 3.512662245652e+00 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 3.512662245652e+00 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 6.230314124713e-16 
>>>   Linear solve converged due to CONVERGED_RTOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   2 SNES Function norm 8.969285922373e-01 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 8.969285922373e-01 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 0.000000000000e+00 
>>>   Linear solve converged due to CONVERGED_ATOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   3 SNES Function norm 4.863816734540e-01 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 4.863816734540e-01 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 0.000000000000e+00 
>>>   Linear solve converged due to CONVERGED_ATOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   4 SNES Function norm 3.512070785520e-01 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 3.512070785520e-01 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 0.000000000000e+00 
>>>   Linear solve converged due to CONVERGED_ATOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   5 SNES Function norm 2.769700293115e-01 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 2.769700293115e-01 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 1.104778916974e-16 
>>>   Linear solve converged due to CONVERGED_RTOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   6 SNES Function norm 2.055345318150e-01 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 2.055345318150e-01 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 0.000000000000e+00 
>>>   Linear solve converged due to CONVERGED_ATOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   7 SNES Function norm 1.267482220786e-01 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 1.267482220786e-01 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 1.498679601680e-17 
>>>   Linear solve converged due to CONVERGED_RTOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>   8 SNES Function norm 3.468150619264e-02 
>>>  ++++++++++++ in jac shell +++++++++++
>>>     0 KSP Residual norm 3.468150619264e-02 
>>>  === start mymult ===
>>>  === done mymult ===
>>>     1 KSP Residual norm 5.944160522951e-18 
>>>   Linear solve converged due to CONVERGED_RTOL iterations 1
>>>  === start mymult ===
>>>  === done mymult ===
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  ( in rhs )
>>>  ( leave rhs )
>>>  === start mymult ===
>>>  === done mymult ===
>>> Nonlinear solve did not converge due to DIVERGED_LINE_SEARCH iterations 8
>>> Number of SNES iterations =     8
>>> 
>>> After each "Linear solve converged due to CONVERGED_ATOL iterations", the code starts to do mymult again. So I thought it did an extra (unwanted) KSP iteration. I would like to ask if this extra iteration could be disabled, or maybe I am wrong about it.
>>> 
>>> Best regards,
>>> 
>>> Yi
>>> 
>>> On 1/30/24 18:35, Barry Smith wrote:
>>>> 
>>>>   How do I see a difference? What does "hence ruin my previous converged KSP result" mean? A different answer at the end of the KSP solve?
>>>> 
>>>> $ ./joe > joe.basic
>>>> ~/Src/petsc/src/ksp/ksp/tutorials (barry/2023-09-15/fix-log-pcmpi=) arch-fix-log-pcmpi
>>>> $ ./joe -ksp_monitor -ksp_converged_reason -snes_monitor > joe.monitor
>>>> ~/Src/petsc/src/ksp/ksp/tutorials (barry/2023-09-15/fix-log-pcmpi=) arch-fix-log-pcmpi
>>>> $ diff joe.basic joe.monitor 
>>>> 0a1,36
>>>> >   0 SNES Function norm 6.041522986797e+00 
>>>> >     0 KSP Residual norm 6.041522986797e+00 
>>>> >     1 KSP Residual norm 5.065392549852e-16 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   1 SNES Function norm 3.512662245652e+00 
>>>> >     0 KSP Residual norm 3.512662245652e+00 
>>>> >     1 KSP Residual norm 6.230314124713e-16 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   2 SNES Function norm 8.969285922373e-01 
>>>> >     0 KSP Residual norm 8.969285922373e-01 
>>>> >     1 KSP Residual norm 0.000000000000e+00 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   3 SNES Function norm 4.863816734540e-01 
>>>> >     0 KSP Residual norm 4.863816734540e-01 
>>>> >     1 KSP Residual norm 0.000000000000e+00 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   4 SNES Function norm 3.512070785520e-01 
>>>> >     0 KSP Residual norm 3.512070785520e-01 
>>>> >     1 KSP Residual norm 0.000000000000e+00 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   5 SNES Function norm 2.769700293115e-01 
>>>> >     0 KSP Residual norm 2.769700293115e-01 
>>>> >     1 KSP Residual norm 1.104778916974e-16 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   6 SNES Function norm 2.055345318150e-01 
>>>> >     0 KSP Residual norm 2.055345318150e-01 
>>>> >     1 KSP Residual norm 1.535110861002e-17 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   7 SNES Function norm 1.267482220786e-01 
>>>> >     0 KSP Residual norm 1.267482220786e-01 
>>>> >     1 KSP Residual norm 1.498679601680e-17 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> >   8 SNES Function norm 3.468150619264e-02 
>>>> >     0 KSP Residual norm 3.468150619264e-02 
>>>> >     1 KSP Residual norm 5.944160522951e-18 
>>>> >   Linear solve converged due to CONVERGED_RTOL_NORMAL iterations 1
>>>> 
>>>> 
>>>> 
>>>>> On Jan 30, 2024, at 11:19 AM, Yi Hu <y.hu at mpie.de> <mailto:y.hu at mpie.de> wrote:
>>>>> 
>>>>> Dear PETSc team,
>>>>>  
>>>>> I am still trying to sort out my previous thread https://lists.mcs.anl.gov/pipermail/petsc-users/2024-January/050079.html using a minimal working example. However, I encountered another problem. Basically I combined the basic usage of SNES solver and shell matrix and tried to make it work. The jacobian of my snes is replaced by a customized MATOP_MULT. The minimal example code can be viewed here https://github.com/hyharry/small_petsc_test/blob/master/test_shell_jac/ex1f.F90
>>>>>  
>>>>> When running with -ksp_monitor -ksp_converged_reason, it shows an extra mymult step, and hence ruin my previous converged KSP result. Implement a customized converged call-back also does not help. I am wondering how to skip this extra ksp iteration. Could anyone help me on this?
>>>>>  
>>>>> Thanks for your help.
>>>>>  
>>>>> Best wishes,
>>>>> Yi
>>>>> 
>>>>> 
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>>> Max-Planck-Institut für Eisenforschung GmbH
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>>> Amtsgericht Düsseldorf
>>>  
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>>>  
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>>> Please consider that invitations and e-mails of our institute are 
>>> only valid if they end with …@mpie.de. 
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>>> Bitte beachten Sie, dass Einladungen zu Veranstaltungen und E-Mails
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>> 
> 
> 
> -------------------------------------------------
> Stay up to date and follow us on LinkedIn, Twitter and YouTube.
> 
> Max-Planck-Institut für Eisenforschung GmbH
> Max-Planck-Straße 1
> D-40237 Düsseldorf
>  
> Handelsregister B 2533 
> Amtsgericht Düsseldorf
>  
> Geschäftsführung
> Prof. Dr. Gerhard Dehm
> Prof. Dr. Jörg Neugebauer
> Prof. Dr. Dierk Raabe
> Dr. Kai de Weldige
>  
> Ust.-Id.-Nr.: DE 11 93 58 514 
> Steuernummer: 105 5891 1000
> 
> 
> Please consider that invitations and e-mails of our institute are 
> only valid if they end with …@mpie.de. 
> If you are not sure of the validity please contact rco at mpie.de
> 
> Bitte beachten Sie, dass Einladungen zu Veranstaltungen und E-Mails
> aus unserem Haus nur mit der Endung …@mpie.de gültig sind. 
> In Zweifelsfällen wenden Sie sich bitte an rco at mpie.de
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