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Aide de Scilab >> Traitement du Signal > xcorr

xcorr

Computes discrete auto or cross correlation

Calling Sequence

[c [,lagindex]] = xcorr(x [,maxlags [,scaling]])
[c [,lagindex]] = xcorr(x,y [,maxlags [,scaling]])

Parameters

x

a vector of real or complex floating point numbers.

y

a vector of real or complex floating point numbers. The default value is x.

maxlags

a scalar with integer value greater than 1. The default value is n. Where n is the maximum of the x and y vector length.

scaling

a character string with possible value: "biased", "unbiased", "coeff", "none". The default value is "none".

c

a vector of real or complex floating point numbers with same orientation as x.

lagindex

a row vector, containing the lags index corresponding to the c values.

Description

  • c=xcorr(x) computes the un-normalized discrete auto correlation: and return in c the sequence of auto correlation lags with n is the length of x
  • xcorr(x,y) computes the un-normalized discrete cross correlation: and return in c the sequence of auto correlation lags with n is the maximum of x and y length's.

If the maxlags argument is given xcorr returns in c the sequence of auto correlation lags . If maxlags is greater than length(x), the first and last values of c are zero.

The scaling argument decribes how is normalized before being returned in c:

  • "biased":c=/n.
  • "unbiased":c=./(n-(-maxlags:maxlags)).
  • "coeff":c=/(norm(x)*norm(y)).

Remark

The corr function computes the "biased" covariance of x and y and only return in c the sequence of auto correlation lags .

Method

This function computes using ifft(fft(x).*conj(fft(y))).

Examples

t = linspace(0, 100, 2000);
                y = 0.8 * sin(t) + 0.8 * sin(2 * t);
                [c, ind] = xcorr(y, "biased");
                plot(ind, c)

See Also

Authors

  • Serge Steer, INRIA

Used Functions

fft

History

VersionDescription
5.4.0 xcorr added.
Scilab Enterprises
Copyright (c) 2011-2017 (Scilab Enterprises)
Copyright (c) 1989-2012 (INRIA)
Copyright (c) 1989-2007 (ENPC)
with contributors
Last updated:
Thu Oct 02 13:54:32 CEST 2014