[petsc-dev] why does this inanity exist?

[Barry Smith]

> On Apr 30, 2017, at 3:19 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> Proposal: add ts->default_adapt_type.  TSCreate_* sets this.  Remove
> TSGetAdapt from TSCreate and move it to TSSetUp and TSSetFromOptions.
> Make TSGetAdapt call TSAdaptSetType(adapt,ts->default_adapt_type).  Now
> there is no "setbyuser", but TS implementations can select their
> preferences and those will be ignored if the user calls TSGetAdapt and
> changes it themselves.  And -ts_adapt_type none always works.

  I don't see any immediate flaws in this approach.

> 
> Barry Smith <bsmith at mcs.anl.gov> writes:
> 
>>> 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)
>>> http://ecrc.kaust.edu.sa/
>>> 
>>> 4700 King Abdullah University of Science and Technology
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>>> 
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