[petsc-users] Diagnosing Convergence Issue in Fieldsplit Problem

Thu May 23 11:51:29 CDT 2024

That produces the error:

[0]PETSC ERROR: Residual norm computed by GMRES recursion formula
2.68054e-07 is far from the computed residual norm 6.86309e-06 at restart,
residual norm at start of cycle 2.68804e-07

The rest of the error is identical.

On Thu, May 23, 2024 at 10:46 AM Barry Smith <bsmith at petsc.dev> wrote:

>
>   Use -pc_fieldsplit_0_ksp_type preonly
>
>
>
> On May 23, 2024, at 12:43 PM, Colton Bryant <
> coltonbryant2021 at u.northwestern.edu> wrote:
>
> That produces the following error:
>
> [0]PETSC ERROR: Residual norm computed by GMRES recursion formula
> 2.79175e-07 is far from the computed residual norm 0.000113154 at restart,
> residual norm at start of cycle 2.83065e-07
> [0]PETSC ERROR: See https://urldefense.us/v3/__https://petsc.org/release/faq/__;!!G_uCfscf7eWS!foIaeUuWTMmxtBgnoG5PFWz6Rn81qpoqVF-9tsdAO49hGowu7DDL4ugiusD-4W89x1iziDN2_XvyW9S43rH6Urka-W9kRMxnr_n0sZ1V3gk$  for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.21.0, unknown
> [0]PETSC ERROR: ./mainOversetLS_exe on a arch-linux-c-opt named glass by
> colton Thu May 23 10:41:09 2024
> [0]PETSC ERROR: Configure options --download-mpich --with-cc=gcc
> --with-cxx=g++ --with-debugging=no --with-fc=gfortran COPTFLAGS=-O3
> CXXOPTFLAGS=-O3 FOPTFLAGS=-O3 PETSC_ARCH=arch-linux-c-opt --download-sowing
> [0]PETSC ERROR: #1 KSPGMRESCycle() at
> /home/colton/petsc/src/ksp/ksp/impls/gmres/gmres.c:115
> [0]PETSC ERROR: #2 KSPSolve_GMRES() at
> /home/colton/petsc/src/ksp/ksp/impls/gmres/gmres.c:227
> [0]PETSC ERROR: #3 KSPSolve_Private() at
> /home/colton/petsc/src/ksp/ksp/interface/itfunc.c:905
> [0]PETSC ERROR: #4 KSPSolve() at
> /home/colton/petsc/src/ksp/ksp/interface/itfunc.c:1078
> [0]PETSC ERROR: #5 PCApply_FieldSplit_Schur() at
> /home/colton/petsc/src/ksp/pc/impls/fieldsplit/fieldsplit.c:1203
> [0]PETSC ERROR: #6 PCApply() at
> /home/colton/petsc/src/ksp/pc/interface/precon.c:497
> [0]PETSC ERROR: #7 KSP_PCApply() at
> /home/colton/petsc/include/petsc/private/kspimpl.h:409
> [0]PETSC ERROR: #8 KSPFGMRESCycle() at
> /home/colton/petsc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c:123
> [0]PETSC ERROR: #9 KSPSolve_FGMRES() at
> /home/colton/petsc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c:235
> [0]PETSC ERROR: #10 KSPSolve_Private() at
> /home/colton/petsc/src/ksp/ksp/interface/itfunc.c:905
> [0]PETSC ERROR: #11 KSPSolve() at
> /home/colton/petsc/src/ksp/ksp/interface/itfunc.c:1078
> [0]PETSC ERROR: #12 solveStokes() at cartesianStokesGrid.cpp:1403
>
>
>
> On Thu, May 23, 2024 at 10:33 AM Barry Smith <bsmith at petsc.dev> wrote:
>
>>
>>   Run the failing case with also -ksp_error_if_not_converged so we see
>> exactly where the problem is first detected.
>>
>>
>>
>>
>> On May 23, 2024, at 11:51 AM, Colton Bryant <
>> coltonbryant2021 at u.northwestern.edu> wrote:
>>
>> Hi Barry,
>>
>> Thanks for letting me know about the need to use fgmres in this case. I
>> ran a smaller problem (1230 in the first block) and saw similar behavior in
>> the true residual.
>>
>> I also ran the same problem with the options -fieldsplit_0_pc_type svd
>> -fieldsplit_0_pc_svd_monitor and get the following output:
>>       SVD: condition number 1.933639985881e+03, 0 of 1230 singular values
>> are (nearly) zero
>>       SVD: smallest singular values: 4.132036392141e-03
>> 4.166444542385e-03 4.669534028645e-03 4.845532162256e-03 5.047038625390e-03
>>       SVD: largest singular values : 7.947990616611e+00
>> 7.961437414477e+00 7.961851612473e+00 7.971335373142e+00 7.989870790960e+00
>>
>> I would be surprised if the A_{00} block is ill conditioned as it's just
>> a standard discretization of the laplacian with some rows replaced with
>> ones on the diagonal due to interpolations from the overset mesh. I'm
>> wondering if I'm somehow violating a solvability condition of the problem?
>>
>> Thanks for the help!
>>
>> -Colton
>>
>> On Wed, May 22, 2024 at 6:09 PM Barry Smith <bsmith at petsc.dev> wrote:
>>
>>>
>>>   Thanks for the info. I see you are using GMRES inside the Schur
>>> complement solver, this is ok but when you do you need to use fgmres as the
>>> outer solver. But this is unlikely to be the cause of the exact problem you
>>> are seeing.
>>>
>>>   I'm not sure why the Schur complement KSP is suddenly seeing a large
>>> increase in the true residual norm.  Is it possible the A_{00} block is
>>> ill-conditioned?
>>>
>>>    Can you run with a smaller problem? Say 2,000 or so in the first
>>> block? Is there still a problem?
>>>
>>>
>>>
>>>
>>>
>>> On May 22, 2024, at 6:00 PM, Colton Bryant <
>>> coltonbryant2021 at u.northwestern.edu> wrote:
>>>
>>> Hi Barry,
>>>
>>> I have not used any other solver parameters in the code and the full set
>>> of solver related command line options are those I mentioned in the
>>> previous email.
>>>
>>> Below is the output from -ksp_view:
>>>
>>> KSP Object: (back_) 1 MPI process
>>>   type: gmres
>>>     restart=30, using Classical (unmodified) Gram-Schmidt
>>> Orthogonalization with no iterative refinement
>>>     happy breakdown tolerance 1e-30
>>>   maximum iterations=10000, initial guess is zero
>>>   tolerances: relative=1e-08, absolute=1e-50, divergence=10000.
>>>   left preconditioning
>>>   using PRECONDITIONED norm type for convergence test
>>> PC Object: (back_) 1 MPI process
>>>   type: fieldsplit
>>>     FieldSplit with Schur preconditioner, blocksize = 1, factorization
>>> FULL
>>>     Preconditioner for the Schur complement formed from S itself
>>>     Split info:
>>>     Split number 0 Defined by IS
>>>     Split number 1 Defined by IS
>>>     KSP solver for A00 block
>>>       KSP Object: (back_fieldsplit_0_) 1 MPI process
>>>         type: gmres
>>>           restart=30, using Classical (unmodified) Gram-Schmidt
>>> Orthogonalization with no iterative refinement
>>>           happy breakdown tolerance 1e-30
>>>         maximum iterations=10000, initial guess is zero
>>>         tolerances: relative=1e-05, absolute=1e-50, divergence=10000.
>>>         left preconditioning
>>>         using PRECONDITIONED norm type for convergence test
>>>       PC Object: (back_fieldsplit_0_) 1 MPI process
>>>         type: lu
>>>           out-of-place factorization
>>>           tolerance for zero pivot 2.22045e-14
>>>           matrix ordering: nd
>>>           factor fill ratio given 5., needed 8.83482
>>>             Factored matrix follows:
>>>               Mat Object: (back_fieldsplit_0_) 1 MPI process
>>>                 type: seqaij
>>>                 rows=30150, cols=30150
>>>                 package used to perform factorization: petsc
>>>                 total: nonzeros=2649120, allocated nonzeros=2649120
>>>                   using I-node routines: found 15019 nodes, limit used
>>> is 5
>>>         linear system matrix = precond matrix:
>>>         Mat Object: (back_fieldsplit_0_) 1 MPI process
>>>           type: seqaij
>>>           rows=30150, cols=30150
>>>           total: nonzeros=299850, allocated nonzeros=299850
>>>           total number of mallocs used during MatSetValues calls=0
>>>             using I-node routines: found 15150 nodes, limit used is 5
>>>     KSP solver for S = A11 - A10 inv(A00) A01
>>>       KSP Object: (back_fieldsplit_1_) 1 MPI process
>>>         type: gmres
>>>           restart=30, using Classical (unmodified) Gram-Schmidt
>>> Orthogonalization with no iterative refinement
>>>           happy breakdown tolerance 1e-30
>>>         maximum iterations=10000, initial guess is zero
>>>         tolerances: relative=1e-08, absolute=1e-50, divergence=10000.
>>>         left preconditioning
>>>         using PRECONDITIONED norm type for convergence test
>>>       PC Object: (back_fieldsplit_1_) 1 MPI process
>>>         type: none
>>>         linear system matrix = precond matrix:
>>>         Mat Object: (back_fieldsplit_1_) 1 MPI process
>>>           type: schurcomplement
>>>           rows=15000, cols=15000
>>>             Schur complement A11 - A10 inv(A00) A01
>>>             A11
>>>               Mat Object: (back_fieldsplit_1_) 1 MPI process
>>>                 type: seqaij
>>>                 rows=15000, cols=15000
>>>                 total: nonzeros=74700, allocated nonzeros=74700
>>>                 total number of mallocs used during MatSetValues calls=0
>>>                   not using I-node routines
>>>             A10
>>>               Mat Object: 1 MPI process
>>>                 type: seqaij
>>>                 rows=15000, cols=30150
>>>                 total: nonzeros=149550, allocated nonzeros=149550
>>>                 total number of mallocs used during MatSetValues calls=0
>>>                   not using I-node routines
>>>             KSP solver for A00 block viewable with the additional option
>>> -back_fieldsplit_0_ksp_view
>>>             A01
>>>               Mat Object: 1 MPI process
>>>                 type: seqaij
>>>                 rows=30150, cols=15000
>>>                 total: nonzeros=149550, allocated nonzeros=149550
>>>                 total number of mallocs used during MatSetValues calls=0
>>>                   using I-node routines: found 15150 nodes, limit used
>>> is 5
>>>   linear system matrix = precond matrix:
>>>   Mat Object: (back_) 1 MPI process
>>>     type: seqaij
>>>     rows=45150, cols=45150
>>>     total: nonzeros=673650, allocated nonzeros=673650
>>>     total number of mallocs used during MatSetValues calls=0
>>>       has attached null space
>>>       using I-node routines: found 15150 nodes, limit used is 5
>>>
>>> Thanks again!
>>>
>>> -Colton
>>>
>>> On Wed, May 22, 2024 at 3:39 PM Barry Smith <bsmith at petsc.dev> wrote:
>>>
>>>>
>>>>   Are you using any other command line options or did you hardwire any
>>>> solver parameters in the code with, like, KSPSetXXX() or PCSetXXX() Please
>>>> send all of them.
>>>>
>>>>   Something funky definitely happened when the true residual norms
>>>> jumped up.
>>>>
>>>>   Could you run the same thing with -ksp_view and don't use any thing
>>>> like -ksp_error_if_not_converged so we can see exactly what is being run.
>>>>
>>>>   Barry
>>>>
>>>>
>>>> On May 22, 2024, at 3:21 PM, Colton Bryant <
>>>> coltonbryant2021 at u.northwestern.edu> wrote:
>>>>
>>>> This Message Is From an External Sender
>>>> This message came from outside your organization.
>>>> Hello,
>>>>
>>>> I am solving the Stokes equations on a MAC grid discretized by finite
>>>> differences using a DMSTAG object. I have tested the solver quite
>>>> extensively on manufactured problems and it seems to work well. As I am
>>>> still just trying to get things working and not yet worried about speed I
>>>> am using the following solver options:
>>>> -pc_type fieldsplit
>>>> -pc_fieldsplit_detect_saddle_point
>>>> -fieldsplit_0_pc_type lu
>>>> -fieldsplit_1_ksp_rtol 1.e-8
>>>>
>>>> However I am now using this solver as an inner step of a larger code
>>>> and have run into issues. The code repeatedly solves the Stokes equations
>>>> with varying right hand sides coming from changing problem geometry (the
>>>> solver is a part of an overset grid scheme coupled to a level set method
>>>> evolving in time). After a couple timesteps I observe the following output
>>>> when running with -fieldsplit_1_ksp_converged_reason
>>>> -fieldsplit_1_ksp_monitor_true_residual:
>>>>
>>>> Residual norms for back_fieldsplit_1_ solve.
>>>>     0 KSP preconditioned resid norm 2.826514299465e-02 true resid norm
>>>> 2.826514299465e-02 ||r(i)||/||b|| 1.000000000000e+00
>>>>     1 KSP preconditioned resid norm 7.286621865915e-03 true resid norm
>>>> 7.286621865915e-03 ||r(i)||/||b|| 2.577953300039e-01
>>>>     2 KSP preconditioned resid norm 1.500598474492e-03 true resid norm
>>>> 1.500598474492e-03 ||r(i)||/||b|| 5.309007192273e-02
>>>>     3 KSP preconditioned resid norm 3.796396924978e-04 true resid norm
>>>> 3.796396924978e-04 ||r(i)||/||b|| 1.343137349666e-02
>>>>     4 KSP preconditioned resid norm 8.091057439816e-05 true resid norm
>>>> 8.091057439816e-05 ||r(i)||/||b|| 2.862556697960e-03
>>>>     5 KSP preconditioned resid norm 3.689113122359e-05 true resid norm
>>>> 3.689113122359e-05 ||r(i)||/||b|| 1.305181128239e-03
>>>>     6 KSP preconditioned resid norm 2.116450533352e-05 true resid norm
>>>> 2.116450533352e-05 ||r(i)||/||b|| 7.487846545662e-04
>>>>     7 KSP preconditioned resid norm 3.968234031201e-06 true resid norm
>>>> 3.968234031200e-06 ||r(i)||/||b|| 1.403932055801e-04
>>>>     8 KSP preconditioned resid norm 6.666949419511e-07 true resid norm
>>>> 6.666949419506e-07 ||r(i)||/||b|| 2.358717739644e-05
>>>>     9 KSP preconditioned resid norm 1.941522884928e-07 true resid norm
>>>> 1.941522884931e-07 ||r(i)||/||b|| 6.868965372998e-06
>>>>    10 KSP preconditioned resid norm 6.729545258682e-08 true resid norm
>>>> 6.729545258626e-08 ||r(i)||/||b|| 2.380863687793e-06
>>>>    11 KSP preconditioned resid norm 3.009070131709e-08 true resid norm
>>>> 3.009070131735e-08 ||r(i)||/||b|| 1.064586912687e-06
>>>>    12 KSP preconditioned resid norm 7.849353009588e-09 true resid norm
>>>> 7.849353009903e-09 ||r(i)||/||b|| 2.777043445840e-07
>>>>    13 KSP preconditioned resid norm 2.306283345754e-09 true resid norm
>>>> 2.306283346677e-09 ||r(i)||/||b|| 8.159461097060e-08
>>>>    14 KSP preconditioned resid norm 9.336302495083e-10 true resid norm
>>>> 9.336302502503e-10 ||r(i)||/||b|| 3.303115255517e-08
>>>>    15 KSP preconditioned resid norm 6.537456143401e-10 true resid norm
>>>> 6.537456141617e-10 ||r(i)||/||b|| 2.312903968982e-08
>>>>    16 KSP preconditioned resid norm 6.389159552788e-10 true resid norm
>>>> 6.389159550304e-10 ||r(i)||/||b|| 2.260437724130e-08
>>>>    17 KSP preconditioned resid norm 6.380905134246e-10 true resid norm
>>>> 6.380905136023e-10 ||r(i)||/||b|| 2.257517372981e-08
>>>>    18 KSP preconditioned resid norm 6.380440605992e-10 true resid norm
>>>> 6.380440604688e-10 ||r(i)||/||b|| 2.257353025207e-08
>>>>    19 KSP preconditioned resid norm 6.380427156582e-10 true resid norm
>>>> 6.380427157894e-10 ||r(i)||/||b|| 2.257348267830e-08
>>>>    20 KSP preconditioned resid norm 6.380426714897e-10 true resid norm
>>>> 6.380426714004e-10 ||r(i)||/||b|| 2.257348110785e-08
>>>>    21 KSP preconditioned resid norm 6.380426656970e-10 true resid norm
>>>> 6.380426658839e-10 ||r(i)||/||b|| 2.257348091268e-08
>>>>    22 KSP preconditioned resid norm 6.380426650538e-10 true resid norm
>>>> 6.380426650287e-10 ||r(i)||/||b|| 2.257348088242e-08
>>>>    23 KSP preconditioned resid norm 6.380426649918e-10 true resid norm
>>>> 6.380426645888e-10 ||r(i)||/||b|| 2.257348086686e-08
>>>>    24 KSP preconditioned resid norm 6.380426649803e-10 true resid norm
>>>> 6.380426644294e-10 ||r(i)||/||b|| 2.257348086122e-08
>>>>    25 KSP preconditioned resid norm 6.380426649796e-10 true resid norm
>>>> 6.380426649774e-10 ||r(i)||/||b|| 2.257348088061e-08
>>>>    26 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
>>>> 6.380426653788e-10 ||r(i)||/||b|| 2.257348089481e-08
>>>>    27 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
>>>> 6.380426646744e-10 ||r(i)||/||b|| 2.257348086989e-08
>>>>    28 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
>>>> 6.380426650818e-10 ||r(i)||/||b|| 2.257348088430e-08
>>>>    29 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
>>>> 6.380426649518e-10 ||r(i)||/||b|| 2.257348087970e-08
>>>>    30 KSP preconditioned resid norm 6.380426652142e-10 true resid norm
>>>> 6.380426652142e-10 ||r(i)||/||b|| 2.257348088898e-08
>>>>    31 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426646799e-10 ||r(i)||/||b|| 2.257348087008e-08
>>>>    32 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426648077e-10 ||r(i)||/||b|| 2.257348087460e-08
>>>>    33 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426649048e-10 ||r(i)||/||b|| 2.257348087804e-08
>>>>    34 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426648142e-10 ||r(i)||/||b|| 2.257348087483e-08
>>>>    35 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426651079e-10 ||r(i)||/||b|| 2.257348088522e-08
>>>>    36 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650433e-10 ||r(i)||/||b|| 2.257348088294e-08
>>>>    37 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426649765e-10 ||r(i)||/||b|| 2.257348088057e-08
>>>>    38 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650364e-10 ||r(i)||/||b|| 2.257348088269e-08
>>>>    39 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650051e-10 ||r(i)||/||b|| 2.257348088159e-08
>>>>    40 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426651154e-10 ||r(i)||/||b|| 2.257348088549e-08
>>>>    41 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650246e-10 ||r(i)||/||b|| 2.257348088227e-08
>>>>    42 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650702e-10 ||r(i)||/||b|| 2.257348088389e-08
>>>>    43 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426651686e-10 ||r(i)||/||b|| 2.257348088737e-08
>>>>    44 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650870e-10 ||r(i)||/||b|| 2.257348088448e-08
>>>>    45 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426651208e-10 ||r(i)||/||b|| 2.257348088568e-08
>>>>    46 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426651441e-10 ||r(i)||/||b|| 2.257348088650e-08
>>>>    47 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650955e-10 ||r(i)||/||b|| 2.257348088478e-08
>>>>    48 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650877e-10 ||r(i)||/||b|| 2.257348088451e-08
>>>>    49 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426651240e-10 ||r(i)||/||b|| 2.257348088579e-08
>>>>    50 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426650534e-10 ||r(i)||/||b|| 2.257348088329e-08
>>>>    51 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426648615e-10 ||r(i)||/||b|| 2.257348087651e-08
>>>>    52 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
>>>> 6.380426649523e-10 ||r(i)||/||b|| 2.257348087972e-08
>>>>    53 KSP preconditioned resid norm 6.380426652140e-10 true resid norm
>>>> 6.380426652601e-10 ||r(i)||/||b|| 2.257348089061e-08
>>>>    54 KSP preconditioned resid norm 6.380426652125e-10 true resid norm
>>>> 6.380427512852e-10 ||r(i)||/||b|| 2.257348393411e-08
>>>>    55 KSP preconditioned resid norm 6.380426651849e-10 true resid norm
>>>> 6.380603444402e-10 ||r(i)||/||b|| 2.257410636701e-08
>>>>    56 KSP preconditioned resid norm 6.380426646751e-10 true resid norm
>>>> 6.439925413105e-10 ||r(i)||/||b|| 2.278398313542e-08
>>>>    57 KSP preconditioned resid norm 6.380426514019e-10 true resid norm
>>>> 2.674218007058e-09 ||r(i)||/||b|| 9.461186902765e-08
>>>>    58 KSP preconditioned resid norm 6.380425077384e-10 true resid norm
>>>> 2.406759314486e-08 ||r(i)||/||b|| 8.514937691775e-07
>>>>    59 KSP preconditioned resid norm 6.380406171326e-10 true resid norm
>>>> 3.100137288622e-07 ||r(i)||/||b|| 1.096805803957e-05
>>>>     Linear back_fieldsplit_1_ solve did not converge due to
>>>> DIVERGED_BREAKDOWN iterations 60
>>>>
>>>> Any advice on steps I could take to elucidate the issue would be
>>>> greatly appreciated. Thanks so much for any help in advance!
>>>>
>>>> Best,
>>>> Colton Bryant
>>>>
>>>>
>>>>
>>>
>>
>
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