python - Smallest positive float64 number

Question

I need to find a numpy.float64 value that is as close to zero as possible.

Numpy offers several constants that allow to do something similar:

These are both reasonably small, but when I do this

>>> x = np.finfo(np.float64).tiny
>>> x / 2
6.9533558078350043e-310

the result is even smaller. When using an impromptu binary search I can get down to about 1e-323, before the value is rounded down to 0.0.

Is there a constant for this in numpy that I am missing? Alternatively, is there a right way to do this?

Use np.nextafter. Almost a duplicate: stackoverflow.com/questions/6063755/… — ev-br
Thanks, this is exactly what I needed. If you write this as an answer I will gladly accept it. I agree that the topic of the question you linked is similar, but I would have never thought about looking for those keyword with my problem. — m00am
May I ask why you need this? Just to make sure you're not trapped by an XY problem:) — Andras Deak
Primarily out of curiosity. A coworker asked me if I know how to do this and I couldn't come up with a better answer than "Let's ask this on SO". I don't know his precise application though. — m00am
FYI: The floating point values between 0 and np.finfo(np.float64).tiny are known as "denormal" or "subnormal" numbers: en.wikipedia.org/wiki/Denormal_number — Warren Weckesser

ev-br ev-br · Accepted Answer · 2016-07-20T12:25:15

Use np.nextafter.

>>> import numpy as np
>>> np.nextafter(0, 1)
4.9406564584124654e-324
>>> np.nextafter(np.float32(0), np.float32(1))
1.4012985e-45