[Python-ideas] math.nextafter

[Juraj Sukop]

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))
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