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

[Barry Smith]

> On Sep 16, 2020, at 11:23 PM, 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.

  Sounds a bit like a non-smoother (Gauss-Seidel type), speculating based on these few words.
> 
> 
> 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.)