[petsc-users] Issue of mg_coarse_ksp not converge

[Matthew Knepley]

On Sun, Oct 1, 2017 at 9:53 PM, Wenbo Zhao <zhaowenbo.npic at gmail.com> wrote:

> 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.
>

I mean, why are you setting this at all. Just do not set the coarse solver.
The default should work fine.

  Thanks,

    Matt


> 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/>
>>
>
>


-- 
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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