[Python-ideas] math.nextafter

[M.-A. Lemburg]

On 06.02.2017 13:22, Juraj Sukop wrote:
> On Mon, Feb 6, 2017 at 11:29 AM, M.-A. Lemburg <mal at egenix.com> wrote:
> 
>>
>> Juraj: Could you provide some use cases, where such a function
>> would help in Python applications ? (I can see use cases
>> written in C, but due to the low level, find it hard to
>> believe that people would use this at the Python level)
>>
> 
> In my case, `nextafter` would be used to check if a number is close to
> polynomial zero, e.g.:
> 
>     def f(x):
>         return 2.0*x**3 - 3.0*x**2 + 5.0*x - 7.0
> 
>     # x = 1.4455284586795218
>     x = 1.445528458679522
>     # x = 1.4455284586795223
>     # x = 1.4455284586795225
> 
>     left = nextafter(x, -float('inf'))
>     right = nextafter(x, float('inf'))
> 
>     print((f(left) < 0.0) != (f(x) < 0.0) or (f(x) < 0.0) != (f(right) <
> 0.0))

Isn't this something you can do with math.isclose() ?

This would even give you a predefined error range,
not a dynamic one.

-- 
Marc-Andre Lemburg
eGenix.com

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