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

Mon Feb 5 15:18:23 CST 2024

Dear Barry,

the code is attached.

Just to let you know. When I commented out MatShellSetContext() in 
FormJacobianShell(), then the code seems to work, meaning that the base 
vector is passed to shell matrix context behind the scene.

Best regards,

Yi

On 2/5/24 19:09, Barry Smith wrote:
>
>   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> 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> wrote:
>>>>>>
>>>>>> Dear PETSc team,
>>>>>> I am still trying to sort out my previous 
>>>>>> threadhttps://lists.mcs.anl.gov/pipermail/petsc-users/2024-January/050079.htmlusing 
>>>>>> 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 
>>>>>> herehttps://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
>>>> 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.
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>> 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.
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