[Python-ideas] math.nextafter

[David Mertz]

Marc-André slightly misspelled the recent-ish addition of math.isclose(),
but I agree that it is absolutely where a "nextafter" belongs.

The function signature is already relatively complex to cover several
different but related use cases.  I.e.:

    is_close(a, b, *, rel_tol=1e-09, abs_tol=0.0) -> bool

I think an additional keyword-only argument for `nextafter_tol` (maybe a
different spelling) would fit very naturally there.  This would allow
someone to specify 1 for that degree of closeness, but it would also allow
them to specify some integer larger than 1 without needed to write a loop
calling `nextafter()` repeatedly.

Yours, David...

On Fri, Feb 24, 2017 at 5:29 AM, M.-A. Lemburg <mal at egenix.com> wrote:

> Perhaps closeto() could be extended to address the use case:
>
> "Match anything within N number of smallest float representable
> intervals around float value x"
>
> https://www.python.org/dev/peps/pep-0485/
>
> This could then be used to detect cases where it doesn't
> make sense to run additional rounds of refinement to
> find roots or local minima, since IEEE floats simply don't
> provide enough accuracy to dig deeper.
>


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