[petsc-dev] change default KSP max iterations

[Dave May]

Or alternatively, the options set used to define the test should include a
sensible value of -ksp_max_it and include the option -ksp_converged_reason.
If divergence occurred, then the string written to stdout indicating the
reason for termination would provide sufficient information (even with
diff) to determine that the test failed.

However, I can appreciate that this would require a massive overhaul of all
the current test suite.

Given the current test infrastructure used by PETSc, how could one could
easily impose a time limit on each test without making a huge mess inside
the makefile? Putting all the options and bash used to verify the tests
inside the makefiles is already pretty hairy.


On 14 October 2014 14:15, Jed Brown <jed at jedbrown.org> wrote:

> 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?
>
>
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