[petsc-users] Issue of mg_coarse_ksp not converge

Mon Oct 2 08:51:32 CDT 2017

Please send the output with -st_ksp_view and -st_ksp_monitor and we can
start to debug it.

You mentioned that B is not symmetric. I assume it is elliptic (diffusion).
Where does the asymmetry come from?

On Mon, Oct 2, 2017 at 9:39 AM, Wenbo Zhao <zhaowenbo.npic at gmail.com> wrote:

> Matt,
> Thanks for your reply.
> For the defalt option doesnt work firstly( -st_ksp_type gmres -st_pc_type
> gamg -st_pc_gamg_type agg -st_pc_gamg_agg_nsmooths 1), I tried to test
> those options.
>
> Wenbo
>
> On Mon, Oct 2, 2017 at 9:08 PM, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Mon, Oct 2, 2017 at 8:30 AM, Wenbo Zhao <zhaowenbo.npic at gmail.com>
>> wrote:
>>
>>> Matt
>>>
>>> Because I am not clear about what will happen using 'preonly' for large
>>> scale problem.
>>>
>>
>> The size of the problem has nothing to do with 'preonly'. All it means is
>> to apply a preconditioner without a Krylov solver.
>>
>>
>>> It seems to use a direct solver from below,
>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/
>>> KSP/KSPPREONLY.html
>>>
>>
>> However, I still cannot understand why you would change the default?
>>
>>   Matt
>>
>>
>>>
>>> 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/%7Emk51/>
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> 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/%7Emk51/>
>>>>
>>>
>>>
>>
>>
>> --
>> 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/%7Emk51/>
>>
>
>
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