[petsc-users] Problem running ex54f with GAMG

[Barry Smith]

  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>