[petsc-users] Issue of mg_coarse_ksp not converge

[Wenbo Zhao]

Matt

Because I am not clear about what will happen using 'preonly' for large
scale problem.

It seems to use a direct solver from below,
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPPREONLY.html

Thanks!
Wenbo

On Mon, Oct 2, 2017 at 5:09 PM, Matthew Knepley <knepley at gmail.com> wrote:

> 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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