[PYTHON MATRIX-SIG] autocorrelation functions?

[Rob.Hooft@embl-heidelberg.de]

>>>>> "DA" == David Ascher <da@maigret.cog.brown.edu> writes:

 DA> What's a smart (read efficient, and possibly neat) way of doing
 DA> autocorrelation in NumPython?  I'm looking for both 1D and 2D
 DA> with a city-block metric to start with (a cartesian metric would
 DA> be good too, but I suspect that's harder to optimize).

 DA> I'm sure there's a good way to do this, I just can't figure it
 DA> out...

Isn't the O(n^2) operation of autocorrelation mathematically
equivalent to the O(n ln n) auto-convolution operation?

    ac(x)=inverse_fft(fft(x)^2)

Rob
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