[petsc-dev] change default KSP max iterations

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:

>   Does anyone object if I change the default KSP max iterations from 10,000 to 250? 
>
>   The rational is that 10,000 is absurd and if you don’t see convergence by 250 it generally is pretty hopeless. Users, of course, can set a higher max it.

This depends a bit on the problem.  Iterative methods for high-frequency
problems often need a lot of iterations, for example.

My concern is mostly for people that only every once in a while use more
than 250 iterations, the solve fails (confusingly because it "used to
work"), and they have to start over.  Also that just to demonstrate
simple scaling behavior with an example like KSP ex2, you'll need to
bump up the max iterations.

Does the marginal value of saving seconds/minutes(?) for a solver to
reach 10k iterations (when you forgot to enable enough monitoring to
know what's happening) offset the confusion and alleged misbehavior for
the people that want to keep iterating?
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