[petsc-dev] change default KSP max iterations

[Jed Brown]

This can't be fixed simply by reducing 10000. After all, 250^2 is larger and that's just one more level of nesting.

We could set time limits on tests and kill them if they don't complete.

On October 14, 2014 6:28:12 AM CDT, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>On Oct 13, 2014, at 10:30 PM, Jed Brown <jed at jedbrown.org> wrote:
>
>> 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(?)
>
>8+ hours is how long one of the (pretty small) nightly test examples
>that used inner outer iterations (when someone screwed up the code so
>the outer did not converge). Normally the example took < 10 iterations
>and ran very quickly. 
>
>
>
>
>> 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?