[Numpy-discussion] Bug in numpy.correlate documentation

[David Goldsmith]

Looks like Wolfram MathWorld would favor the docstring, but the possibility
of a "use-domain" dependency seems plausible (after all, a similar dilemma
is observed, e.g., w/ the Fourier Transform)--I guess one discipline's
future is another discipline's past. :-)

http://mathworld.wolfram.com/Autocorrelation.html

DG

Date: Tue, 8 Oct 2013 20:10:41 +0100

> From: Richard Hattersley <rhattersley at gmail.com>
> Subject: Re: [Numpy-discussion] Bug in numpy.correlate documentation
> To: Discussion of Numerical Python <numpy-discussion at scipy.org>
> Message-ID:
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> fw at mail.gmail.com>
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>
> Hi Bernard,
>
> Looks like you're on to something - two other people have raised this
> discrepancy before: https://github.com/numpy/numpy/issues/2588.
> Unfortunately, when it comes to resolving the discrepancy one of the
> previous comments takes the opposite view. Namely, that the docstring is
> correct and the code is wrong.
>
> Do different domains use different conventions here? Are there some
> references to back up one stance or another?
>
> But all else being equal, I'm guessing there'll be far more appetite for
> updating the documentation than the code.
>
> Regards,
> Richard Hattersley
>
>
> On 7 October 2013 22:09, Bernhard Spinnler <Bernhard.Spinnler at gmx.net
> >wrote:
>
> > The numpy.correlate documentation says:
> >
> >         correlate(a, v) = z[k] = sum_n a[n] * conj(v[n+k])
> >
>
<snip>

> > [so] according to the documentation, z should be
> >
> >         z[-1] = a[1] * conj(v[0]) = 4.+0.j
> >         z[0]  = a[0] * conj(v[0]) + a[1] * conj(v[1]) = 2.-2.j
> >         z[1] = a[0] * conj(v[1]) = 0.-1.j
> >
> > which is the time reversed version of what correlate() calculates.
>
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