Re: Bug #1503114

[Daniel J S. <dan...@ie...>]

Petr Mikulik wrote:
>>>> 2)  BUG 1503114        FIX: 1107709 plot [-1:1] x is plotted with
>>>> asymmetric y-axis
>>>
>>>
>>> Floating-point rounding is tricky stuff.  It's completely inevitable
>>> that sometimes, results will surprise people.  All this patch does is
>>> move the surprise from a seemingly obvious place to a less obvious one.
>>>  An axis ending at 2.0000001 has no more business being artificially cut
>>> down to 2.0 than one ending at 2.001.
>>
>>
>> I think it does in some cases, and depends on the range.  I'll 
>> illustrate with two ranges determined by the data input.
>>
>> 2) [-2.0 : 2.0000001]
>>
>> In the first case, yes definitely, the limits have no business being 
>> artificially shrunk.
> 
> 
> What about rounding range limits to the nearest "nice value" in a range of
> 100*MachineEpsilon?

Well, yes that is an alternative.  And it accounts, I think, for most of the problems that would likely arise because of some arithmatic error.  I wouldn't mind seeing a formal use of "MachinePrecision".  There is the definition "DBL_EPSILON".  And it would be nice to have some form of epsilon defined, just like pi is defined, so that user can utilize it in function definitions.

However, I still think that rounding to within 1/500 or 1/1000 the axis range--whatever might be beyond the resolution of the display--is a plausible strategy.  Could even have a definable variable, visual_precision (default 0.001), meaning to round outward to within abs(max - min)*visual_precision.  The user could then turn of the effect by setting visual_precision equal to 0.

Anyway, range rounding should be a topic in the documentation and/or part of the "xrange" documentation somewhere.

Dan