[petsc-users] Problem running ex54f with GAMG

[Barry Smith]

  The GAMG produced an indefinite operator. I don't know if there is a way to detect why this happened or how to stop it.

  You can try -ksp_type gmres and see how that goes since it can handle an indefinite preconditioner.



> On Mar 18, 2022, at 11:53 AM, Fabio Durastante <fabio.durastante at unipi.it> wrote:
> 
> For the default case:
> 
> Linear solve converged due to CONVERGED_ATOL iterations 14
> 
> for the other it tells
> 
> Linear solve did not converge due to DIVERGED_INDEFINITE_PC iterations 2
> 
> that again seems a bit strange to me, since this should be a symmetric V-cycle built on smoothed aggregation that should be definite (and symmetric).
> 
> Fabio
> 
> Il 18/03/22 16:47, Barry Smith ha scritto:
>>   Run with -ksp_converged_reason to have it print why it has stopped the iteration.
>> 
>> 
>>> On Mar 18, 2022, at 11:44 AM, Fabio Durastante <fabio.durastante at unipi.it> wrote:
>>> 
>>> Hi everybody,
>>> 
>>> I'm trying to run the rotated anisotropy example ex54f using CG and GAMG as preconditioner, I run it with the command:
>>> 
>>> mpirun -np 2 ./ex54f -ne 1011 \
>>> -theta 18.0 \
>>> -epsilon 100.0 \
>>> -pc_type gamg \
>>> -pc_gamg_type agg \
>>> -log_view \
>>> -log_trace \
>>> -ksp_view \
>>> -ksp_monitor \
>>> -ksp_type cg \
>>> -mg_levels_pc_type jacobi \
>>> -mg_levels_ksp_type richardson \
>>> -mg_levels_ksp_max_it 4 \
>>> -ksp_atol 1e-9 \
>>> -ksp_rtol 1e-12
>>> 
>>> But the KSP CG seems to stop just after two iterations:
>>> 
>>>   0 KSP Residual norm 6.666655711717e-02
>>>   1 KSP Residual norm 9.859661350927e-03
>>> 
>>> I'm attaching the full log, the problem seems to appear when I modify the value of epsilon, if I leave it to the default (1.0) it prints
>>> 
>>>   0 KSP Residual norm 5.862074869050e+00
>>>   1 KSP Residual norm 5.132711016122e-01
>>>   2 KSP Residual norm 1.198566629717e-01
>>>   3 KSP Residual norm 1.992885901625e-02
>>>   4 KSP Residual norm 4.919780086064e-03
>>>   5 KSP Residual norm 1.417045143681e-03
>>>   6 KSP Residual norm 3.559622318760e-04
>>>   7 KSP Residual norm 9.270786187701e-05
>>>   8 KSP Residual norm 1.886403709163e-05
>>>   9 KSP Residual norm 2.940634415714e-06
>>>  10 KSP Residual norm 5.015043022637e-07
>>>  11 KSP Residual norm 9.760219712757e-08
>>>  12 KSP Residual norm 2.320857464659e-08
>>>  13 KSP Residual norm 4.563772507631e-09
>>>  14 KSP Residual norm 8.896675476997e-10
>>> 
>>> that is very strange because the case with epsilon 1 should be easier.
>>> 
>>> Any help with this would be great.
>>> 
>>> Thank you very much,
>>> 
>>> Fabio Durastante
>>> <log_ex54f.txt>