[Python-ideas] Way to check for floating point "closeness"?

[Neil Girdhar]

You can always disable atol by setting atol to zero.  I really don't see
what's wrong with their implementation.

On Thu, Jan 15, 2015 at 5:50 PM, Chris Barker <chris.barker at noaa.gov> wrote:

> On Thu, Jan 15, 2015 at 1:52 PM, Neil Girdhar <mistersheik at gmail.com>
> wrote:
>
>> The point is that this function is already in Python
>>
>
> I  don't think somethign being in an external package means that we have
> to do it the same way in teh stdlib -- even a widely used and well regarded
> package like numpy. And I say this as someone that has "import numpy" in
> maybe 90% of my python files.
>
> Maybe we should be careful to give it a very distinct name, however, to
> avoid confusion.
>
>
>> and if you want to do something different, you should have a really good
>> reason to do it differently.
>>
>
> I'm not sure I agree, but we do in this case anyway. The truth is, while
> really smart people wrote numpy, many of the algorithms in there did not go
> through nearly the level of review currently required for the python
> standard library
>
>
>>   If you were to add a function to math, say math.close, it should work
>> like numpy.allclose in my opinion.
>>
>> For reference, numpy does this:
>>
>> absolute(*a* - *b*) <= (*atol* + *rtol* * absolute(*b*))
>>
>> where atol is an absolute tolerance and rtol is a relative tolerance
>> (relative to the actual value b).  This subsumes most of the proposals here.
>>
>
> adding atol  in there "takes care of" the near zero and straddleing zero
> issue ( I suspect that's why it's done that way), but it is fatally wrong
> for values much less than 1.0 --  the atol totally overwhelms the rtol.
>
> See my post earlier today.
>
> -Chris
>
>
> --
>
> Christopher Barker, Ph.D.
> Oceanographer
>
> Emergency Response Division
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>
> Chris.Barker at noaa.gov
>
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