[petsc-dev] why does this inanity exist?

Barry Smith bsmith at mcs.anl.gov
Sun Apr 30 11:09:11 CDT 2017

> On Apr 30, 2017, at 8:39 AM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> On 30 April 2017 at 05:53, Barry Smith <bsmith at mcs.anl.gov> wrote:
>> TS already had mechanisms to turn on or off adaptivity (presumably) so why would an individual type need to reproduce this functionality except to drive users insane?
> We do not have a clear mechanism for a TS subtype to decide on whether
> adaptivity should be turn on or off by default. The rationale to turn
> it off by default are more or less described in other related email:
> the error estimator is bad quality (or lower order than the one of the
> LTE of the method).

   Why isn't the default just switched when the subtype (with a bad adapter) is selected by the user?

   The reason is that the user may have already manually turned on the adapter and you don't want PETSc switching it secretly later?

   Do we need then to have a flag in TS - adaptsetbyuser? and only change the default if that flag is not on?

   I prefer not to have setbyuser flags in PETSc but sometimes it seems we cannot live without them.

> Please note that THETA and ALPHA do use the standard TSAdapt
> infrastructure, the only thing this "use adapt" flag does is to turn
> it off by default. If you consider it appropriate, I can remove all
> that code for the "use adapt" flag in THETA and ALPHA, users can then
> turn off adaptivity with `-ts_adapt_type none`.

   Yes, I don't understand why users should not just use -ts_adapt_type none. 
> Barry, just read my other email about issues with the LTE as computed
> in THETA and ALPHA , take a decision on it and I'll promptly fire up a
> PR for your review.
> -- 
> Lisandro Dalcin
> ============
> Research Scientist
> Computer, Electrical and Mathematical Sciences & Engineering (CEMSE)
> Extreme Computing Research Center (ECRC)
> King Abdullah University of Science and Technology (KAUST)
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