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ENH: Integer gcd function #8772

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brsr opened this issue Mar 11, 2017 · 1 comment
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ENH: Integer gcd function #8772

brsr opened this issue Mar 11, 2017 · 1 comment
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@eric-wieser
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01 - Enhancement component: numpy._core

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@brsr
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brsr commented Mar 11, 2017

Essentially, math.gcd, but operating on numpy arrays with dtype= something in the int family.

>>> a = np.arange(4)
>>> b = np.arange(10,14)
>>> np.gcd(a, b)
array([10, 1, 2, 1])

Would support broadcasting:

>>> c = 2
>>> np.gcd(b, c)
array([2, 1, 2, 1])

Might want to have a version that operates on multiple values (more than 2) on an axis of a multivariable array:

>>> d = np.arange(9).reshape((3, 3))
>>> np.gcd_along_axis(d, axis=1)
array([3, 1, 1])

(This is slightly related to #4829.)
@eric-wieser
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eric-wieser commented Mar 11, 2017 •
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Sounds like you're after a gufunc for gcd (and why not lcm as well?)

Although lcm could be implemented as a regular ufunc here and then you could use np.lcm.reduce(d, axis=...) for your second case. That wouldn't work for gcd, although you've made me thing about ways it could be made to work (#8773). - wait, turns out I'm an idiot, and gcd is associative

@eric-wieser eric-wieser mentioned this issue Mar 12, 2017
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@eric-wieser eric-wieser self-assigned this Mar 12, 2017
@eric-wieser eric-wieser mentioned this issue Mar 12, 2017
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eric-wieser added a commit to eric-wieser/numpy that referenced this issue Dec 13, 2017
@eric-wieser
ENH: Add gcd and lcm ufuncs
7ab0f15 
Fixes numpy#8772
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