On Tue, 03 Jan 2017, Stephan Hoyer wrote:
> >> testing on stable debian box with elderly numpy, where it does behave
> >> sensibly:
> >> $> python -c "import numpy; print('numpy version: ', numpy.__version__);
> >> a=2; b=-2; print(pow(a,b)); print(pow(numpy.array(a), b))"
> >> ('numpy version: ', '1.8.2')
> >> 0.25
> >> 0
> >> what am I missing?
> 2 ** -2 should be 0.25.
> On old versions of NumPy, you see the the incorrect answer 0. We are now
> preferring to give an error rather than the wrong answer.
it is correct up to casting/truncating to an int for the desire to
maintain the int data type -- the same as
>>> int(0.25)
0
>>> 1/4
0
or even
>>> np.arange(5)/4
array([0, 0, 0, 0, 1])
so it is IMHO more of a documented feature and I don't see why pow needs
to get all so special. Sure thing, in the bring future, unless
in-place operation is demanded I would have voted for consistent float
output.
--
Yaroslav O. Halchenko
Center for Open Neuroscience http://centerforopenneuroscience.org
Dartmouth College, 419 Moore Hall, Hinman Box 6207, Hanover, NH 03755
Phone: +1 (603) 646-9834 Fax: +1 (603) 646-1419
WWW: http://www.linkedin.com/in/yarik
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