[SciPy-Dev] Possibly a bug in scipy.spatial.distance.mahalanobis

[Simen Langseth]

Dear Warren Weckesser

Thanks for your explanation, and sorry for my ignorance.
Your answer made me confidence in using Scipy functions.



On Mon, Dec 29, 2014 at 11:27 PM, Warren Weckesser <
warren.weckesser at gmail.com> wrote:

>
>
> On Mon, Dec 29, 2014 at 6:53 AM, Simen Langseth <simlangen at gmail.com>
> wrote:
>
>> Dear Scipy Developers:
>>
>> The documentation below mentions the following for the formula of
>> mahalanobis distance:
>>
>> [image: \sqrt{ (u-v) V^{-1} (u-v)^T }]
>>
>>
>> http://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.spatial.distance.mahalanobis.html#scipy.spatial.distance.mahalanobis
>>
>> However, in the following source code, the transpose of the delta seems
>> to be missing.
>>
>> u = _validate_vector(u) v = _validate_vector(v)VI = np.atleast_2d(VI)delta
>> = u - vm = np.dot(np.dot(delta, VI), delta)return np.sqrt(m)
>>
>>
>>
>>
>> https://github.com/scipy/scipy/blob/6a7327e8bb8248b2ea165180bc602edf1ab33dda/scipy/spatial/distance.py
>>
>> Please forgive me if I could not understand the source code perfectly.
>>
>>
>
> The x and y arguments to mahalanobis() must be one-dimensional arrays.
> This is enforced by _validate_vector(), which converts arguments with shape
> (N,1) or (1,N) to have shape (N,).  A transpose applied to a
> one-dimensional array doesn't do anything, so there is no need for the
> transpose operation in the code.
>
> Warren
>
>
> Thanks.
>>
>> Simen
>>
>>
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>>
>>
>
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