[petsc-dev] why does this inanity exist?

[Barry Smith]

> On Apr 30, 2017, at 12:53 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> 
> On 30 April 2017 at 19:09, Barry Smith <bsmith at mcs.anl.gov> wrote:
>> 
>>> 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?
>> 
> 
> Yes, indeed. We have the usual fight between explicit API calls in
> code interacting with SetType() and SetFromOptions().
> 
> However, after my refactoring of TSAdapt, maybe we are closer to get
> something that works better.
> 
> 
>>   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.
>> 
> 
> I don't like any setbyuser flags either.
> 
>>> 
>>> 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.
>> 
> 
> These "use adapt" flags were just an attempt to not surprise users
> with TSTHETA changing previous behavior. However, as the error
> estimator is very conservative, I don't really see a problem with
> having adaptivity on by default in THETA and ALPHA.
> 
> So Barry, if you are for it, and Jed has no objections, I can fire a
> PR tomorrow removing these crappy "use adapt flags" in favor of  the
> -ts_adapt_type approach.

   Yes. 

   

> 
> @Stefano, this should fix for good your previous complaints/questions
> about "How do I turn on adaptivity on these methods?".
> 
> -- 
> 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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> 
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