[Numpy-discussion] Definition of correlation, correlate and so on ?

Charles R Harris charlesr.harris at gmail.com
Tue Dec 12 07:12:16 CST 2006

On 12/12/06, David Cournapeau <david at ar.media.kyoto-u.ac.jp> wrote:
> Hi,
>     I am polishing some code to compute autocorrelation using fft, and
> when testing the code against numpy.correlate, I realised that I am not
> sure about the definition... There are various function related to
> correlation as far as numpy/scipoy is concerned:
>     numpy.correlate
>     numpy.corrcoef
>     scipy.signal.correlate
>     For me, the correlation between two sequences X and Y at lag t is
> the sum(X[i] * Y*[i+lag]) where Y* is the complex conjugate of Y.
> numpy.correlate does not use the conjugate, scipy.signal.correlate as
> well, and I don't understand numpy.corrcoef. I've never seen complex
> correlation used without the conjugate, so I was curious why this

Neither have I, it is one of those oddities that may have been inherited
from Numeric. I wouldn't mind seeing it changed but it is probably a bit
late for that.

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