[petsc-users] [EXT]Re: Is using PETSc appropriate for this problem

[Matthew Knepley]

On Thu, Sep 17, 2020 at 2:54 PM Alexander B Prescott <
alexprescott at email.arizona.edu> wrote:

> Thank you all for your input. Matt is right, I cannot batch as this
> formulation must be done sequentially.
>
> >>  Sounds a bit like a non-smoother (Gauss-Seidel type), speculating
> based on these few words.
>
> Barry, it is similar to a Gauss-Seidel solver in that solution updates
> from previous solves are used in the most recent Newton solve, though I'm
> not exactly sure what you mean by "non-smoother".
>

He means a nonlinear smoother. You iterate over your domain solving small
nonlinear problems in order to get closer to the solution
of the big nonlinear problem. Depending on what you are doing, it might be
possible to decouple these, which would likely be much
more efficient.

  Thanks,

     Matt


> Best,
> Alexander
>
>
>
> On Thu, Sep 17, 2020 at 6:06 AM Matthew Knepley <knepley at gmail.com> wrote:
>
>> *External Email*
>> On Thu, Sep 17, 2020 at 12:23 AM Jed Brown <jed at jedbrown.org> wrote:
>>
>>> Alexander B Prescott <alexprescott at email.arizona.edu> writes:
>>>
>>> >>      Are the problems of varying nonlinearity, that is will some
>>> converge
>>> >> with say a couple of Newton iterations while others require more, say
>>> 8 or
>>> >> more Newton steps?
>>> >>
>>> > The nonlinearity should be pretty similar, the problem setup is the
>>> same at
>>> > every node but the global domain needs to be traversed in a specific
>>> order.
>>>
>>>
>>> It sounds like you may have a Newton solver now for each individual
>>> problem?  If so, could you make a histogram of number of iterations
>>> necessary to solve?  Does it have a long tail or does every problem take 3
>>> and 4 iterations (for example).
>>>
>>> If there is no long tail, then you can batch.  If there is a long tail,
>>> you really want a solver that does one problem at a time, or a more dynamic
>>> system that checks which have completed and shrinks the active problem
>>> down.  (That complexity has a development and execution time cost.)
>>>
>>
>> He cannot batch if the solves are sequential, as he says above.
>>
>>    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
>>
>> https://www.cse.buffalo.edu/~knepley/
>> <http://www.cse.buffalo.edu/~knepley/>
>>
>
>
> --
> Alexander Prescott
> alexprescott at email.arizona.edu
> PhD Candidate, The University of Arizona
> Department of Geosciences
> 1040 E. 4th Street
> Tucson, AZ, 85721
>


-- 
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.cse.buffalo.edu/~knepley/>
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