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Re: correlation function

Use ListConvolve

data = RandomReal[1000, RandomInteger[{20, 50}]];

n = Length[data]


Simplify[InverseFourier[Fourier[data]^2] ==
  ListConvolve[data, data, {1, 1}]/Sqrt[n]]


Bob Hanlon

On Sun, Nov 18, 2012 at 3:56 AM, jure lapajne <lapajne.jure at> wrote:
> Hello,
> I'm having hard time calculating correlation (autocorrelation) function of
> two lists (list). I'm trying two different ways of calculating it. One way
> is to use fourier transform and second way is to use Mathematica's function
>  ListCorrelate. I get different results but have no idea why. Here's my code:
> korelacija1 = ListCorrelate[data, data, {1, 1}];
> korelacija11 = Abs[InverseFourier[Abs[Fourier[data]]^2]];
> All elements of "data" are real. I have two Abs in second line because for some reason InverseFourier returns small imaginary parts - I know it shouldn't. It's probably only numerical error.
> Thanks for help.

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