[petsc-users] Issue of mg_coarse_ksp not converge

[Wenbo Zhao]

Matt,
Thanks for your reply.
It DOES make no sense for this problem.
But I am not clear about the 'preonly' option. Which solver is used in
preonly? I wonder if 'preonly' is suitable for large scale problem such as
400,000,000 unknowns.
So I tried 'gmres' option and found these error messages.

Could you give me some suggestions?

Thanks.

Wenbo


On Mon, Oct 2, 2017 at 12:34 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Sun, Oct 1, 2017 at 6:49 AM, Wenbo Zhao <zhaowenbo.npic at gmail.com>
> wrote:
>
>> Hi,
>>
>> I met some questions when I use PETSC/SLEPC to solve two-group neutron
>> diffusion equations with finite difference method. The grid is 3*3*3, when
>> DOF on each points is 2. So the matrix size is 54*54.
>> It is generalized eigenvalue problem Ax=\lamda Bx, where B is diagonally
>> dominant matrix but not symmetry.
>> EPS is set as below,
>>  ierr = EPSSetProblemType(eps,EPS_GNHEP);CHKERRQ(ierr);¬
>>  ierr = EPSSetWhichEigenpairs(eps,EPS_LARGEST_REAL);CHKERRQ(ierr);¬
>>
>> Krylovschur is used as eps sovler. GAMG is used as PC.
>> I tried agg_nsmooths and mg_coarse_ksp_type. Only non-smooths and preonly
>> is OK.
>>
>
> Why are you setting the coarse solver. This makes no sense.
>
>    Thanks,
>
>     Matt
>
>
>>
>> Test 1
>> $ make NCORE=1 runkr_nonsmooth
>> mpirun -n 1 ./step-41 \
>>    -st_ksp_type gmres  \
>>    -st_pc_type gamg -st_pc_gamg_type agg -st_pc_gamg_agg_nsmooths 0 \
>>    -st_ksp_view  -mata AMAT.dat -matb BMAT.dat \
>>    -st_mg_coarse_ksp_type preonly   -st_mg_coarse_ksp_monitor  \
>>    -eps_nev 1 -eps_ncv 10  -eps_monitor  -log_view > log_nonsmooth 2>&1
>>
>> Test 2
>> $ make NCORE=1 runkr_smooth
>> mpirun -n 1 ./step-41 \
>>    -st_ksp_type gmres  \
>>    -st_pc_type gamg -st_pc_gamg_type agg -st_pc_gamg_agg_nsmooths 1 \
>>    -st_ksp_view  -mata AMAT.dat -matb BMAT.dat \
>>    -st_mg_coarse_ksp_type preonly   -st_mg_coarse_ksp_monitor  \
>>    -eps_nev 1 -eps_ncv 10  -eps_monitor -log_view > log_smooth 2>&1
>> makefile:43: recipe for target 'runkr_smooth' failed
>> make: *** [runkr_smooth] Error 91
>>
>> Test 3
>> $ make NCORE=1 runkr_gmres
>> mpirun -n 1 ./step-41 \
>>    -st_ksp_type gmres  \
>>    -st_pc_type gamg -st_pc_gamg_type agg -st_pc_gamg_agg_nsmooths 0 \
>>    -st_ksp_view  -mata AMAT.dat -matb BMAT.dat \
>>    -st_mg_coarse_ksp_type gmres  -st_mg_coarse_ksp_monitor
>> -st_mg_coarse_ksp_rtol 1.0e-6 \
>>    -eps_nev 1 -eps_ncv 10  -eps_monitor  -log_view > log_gmres 2>&1
>> makefile:59: recipe for target 'runkr_gmres' failed
>> make: *** [runkr_gmres] Error 91
>>
>> Log files were attched.
>> The matrix file were also attched as AMAT.dat and BMAT.dat.
>>
>> Is it correct? Or something wrong with my code or commad-line?
>>
>> Thanks!
>>
>> Wenbo
>>
>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
>
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