[petsc-users] Problem running ex54f with GAMG

[Fabio Durastante]

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>