Bug report

[Dan Stromberg]

I'm getting:
/usr/local/cpython-2.7/bin/python (2.7.16) bad
    ('numpy version:', '1.16.6')
    Traceback (most recent call last):
      File "./nii", line 31, in <module>
        assert left == right, "{} != {}".format(left, right)
    AssertionError: 86374.0371429 != 86374.0371429
/usr/local/cpython-3.0/bin/python (3.0.1) bad  No numpy found
/usr/local/cpython-3.1/bin/python (3.1.5) bad  No numpy found
/usr/local/cpython-3.2/bin/python (3.2.5) bad  No numpy found
/usr/local/cpython-3.3/bin/python (3.3.7) bad  No numpy found
/usr/local/cpython-3.4/bin/python (3.4.8) bad  No numpy found
/usr/local/cpython-3.5/bin/python (3.5.5) bad
    numpy version: 1.18.5
    Traceback (most recent call last):
      File "./nii", line 31, in <module>
        assert left == right, "{} != {}".format(left, right)
    AssertionError: 86374.03714285714 != 86374.03714285715
/usr/local/cpython-3.6/bin/python (3.6.0) bad
    numpy version: 1.18.1
    Traceback (most recent call last):
      File "./nii", line 31, in <module>
        assert left == right, "{} != {}".format(left, right)
    AssertionError: 86374.03714285714 != 86374.03714285715
/usr/local/cpython-3.7/bin/python (3.7.0) bad
    numpy version: 1.19.0
    Traceback (most recent call last):
      File "./nii", line 31, in <module>
        assert left == right, "{} != {}".format(left, right)
    AssertionError: 86374.03714285714 != 86374.03714285715
/usr/local/cpython-3.8/bin/python (3.8.0) bad
    numpy version: 1.19.0
    Traceback (most recent call last):
      File "./nii", line 31, in <module>
        assert left == right, "{} != {}".format(left, right)
    AssertionError: 86374.03714285714 != 86374.03714285715
/usr/local/cpython-3.9/bin/python (3.9.0) bad
    numpy version: 1.19.4
    Traceback (most recent call last):
      File
"/home/dstromberg/src/stack-overflow,python-list/numpy-initial-incidence/./nii",
line 31, in <module>
        assert left == right, "{} != {}".format(left, right)
    AssertionError: 86374.03714285714 != 86374.03714285715

So the difference is tiny for me, and can be imputed to rounding error.
Multiplying the big terms first before dividing naturally gives less
rounding error.

As far as why your install is having problems, I don't really know.  What
version of numpy are you using?


On Wed, Feb 24, 2021 at 12:12 PM Carla Molina <carlamolinagrane at gmail.com>
wrote:

> I found the following bug (python 3.9.1) when multiplying an array by
> several variables without parentheses; look at the following example:
>
> import numpy as np
>
> NR = 0.25
> N = 60461826
>
> initialINCIDENCE = np.array([1, 50, 100, 150, 200, 250, 300])
> initialINCIDENCE = initialINCIDENCE*N/(100000*7*NR)
> print('First result ' +str(initialINCIDENCE))
>
> initialINCIDENCE = np.array([1, 50, 100, 150, 200, 250, 300])
> initialINCIDENCE = initialINCIDENCE*(N/(100000*7*NR))
> print('Second result ' +str(initialINCIDENCE))
>
> The result given is:
>
> First result [   345.49614857  -7267.86283429  10006.94459429   2739.08176
>   -4528.78107429 -11796.64390857   5478.16352   ]
> Second result [   345.49614857  17274.80742857  34549.61485714
>  51824.42228571  69099.22971429  86374.03714286 103648.84457143]
>
> Clearly both are different, and in particular the first one has no sense to
> me.
> Thank you,
>
> Carla.
> --
> https://mail.python.org/mailman/listinfo/python-list
>