[petsc-users] Setting GAMG options C code

[Matthew Knepley]

On Tue, Jul 4, 2017 at 9:06 AM, Harshad Sahasrabudhe <hsahasra at purdue.edu>
wrote:

>           ierr = PetscOptionsSetValue(NULL, "-st_mg_levels_ksp_type",
>>> "chebyshev");
>>>           chkerr(ierr);
>>>           ierr = PetscOptionsSetValue(NULL, "-st_mg_levels_pc_type",
>>> "jacobi");
>>>           chkerr(ierr);
>>>           ierr = PetscOptionsSetValue(NULL, "-st_mg_levels_ksp_max_it",
>>> "8");
>>>           chkerr(ierr);
>>>           ierr = PetscOptionsSetValue(NULL, "-st_pc_gamg_threshold",
>>> "0.01");
>>>           chkerr(ierr);
>>>
>>
>> I have a different opinion than Jose. I think the above lines are a
>> better way to lock in the setup.
>>
>> 1) It is very difficult to get the order correct when you use the API
>>
>> 2) For deeply nested solvers it can be either inflexible (you assume a
>> structure) or laborious (since
>> you check for certain structures at each level)
>>
>>   Thanks,
>>
>>     Matt
>>
>
> Thanks Matt! I will use it by setting options. I have one question though:
> What happens if there are 2 conflicting options?
>

Last one wins, just like sports.

   Matt

-- 
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

http://www.caam.rice.edu/~mk51/
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