[Numpy-discussion] random.uniform documentation bug?

Robert Kern robert.kern@gmail....
Tue Feb 23 12:29:29 CST 2010


On Tue, Feb 23, 2010 at 08:21, Alan G Isaac <aisaac@american.edu> wrote:
> This behavior does not match the current documentation.
>
>>>> np.random.uniform(low=0.5,high=0.5)
> 0.5
>>>> np.random.uniform(low=0.5,high=0.4)
> 0.48796883601707464
>
> I assume this behavior is intentional and it is
> the documentation that is in error (for the case
> when high<=low)?

Well, the documentation just doesn't really address high<=low. In any
case, the claim that the results are in [low, high) is wrong thanks to
floating point arithmetic. It has exactly the same issues as the
standard library's random.uniform() and should be updated to reflect
that fact:


random.uniform(a, b)
  Return a random floating point number N such that a <= N <= b for a
<= b and b <= N <= a for b < a.

  The end-point value b may or may not be included in the range
depending on floating-point rounding in the equation a + (b-a) *
random().


We should address the high < low case in the documentation because
we're not going to bother raising an exception when high < low.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco


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