cross correlation lag scale

On 6 Feb, 13:16, "john1985" <murray_1...@hotmail.com> wrote:
> >On 6 Feb, 11:55, "john1985" <murray_1...@hotmail.com> wrote:
>
> >> >cxy = xcorr(x,y);
> >> >kv = 1:length(cxy)-lengh(x);
> >> >plot(kv,cxy)
>
> >> >Rune
>
> >> Hi Rune,
> >> I tried your snippet of code but it didn't seem to work as got the
> >> following error>> plot(kv,cordat)
>
> >> ??? Error using ==> plot
> >> Vectors must be the same lengths.
>
> >Try
>
> >kv = (1:length(cxy))-length(x);
>
> >(parentheses added) instead. And test this with as
> >simple data as possible to make sure you understand
> >how it works!
>
> >Test with this script (not tested!):
>
> >N=33;
> >x = reshape(sin((0:N-1)*0.2*pi),N,1);
> >M = 512;
> >y = randn(M,1);
> >K = 128;
> >y(K:K+N-1)=y(K:K+N-1)+x;
> >cxy = xcorr(x,y);
> >kv=(1:N+K-1)-K;
> >plot(kv,cxy);
>
> >If it runs (I don't have access to matlab right now, so I can't
> >test it), it should have a peak near kv = K. Do *not* try
> >to analyze your measured data until you get this script
> >to run, and you understand how and why it works.
> >Rune
>
> Hi Rune,
> I ran your code but I got the ame error as before. I don't really
> understand it as you seem to definr kv twice.

OK, just clear everything:

clear all; close all; clc

and then run the script again. If the error returns, use
the command

whos

and paste the output here.

> Besides that I don't think
> it will help much as the problem i'm having is scaling the x-axis
> according to time.

The script is intended to help you understand the
relation between the x axis and time.

Rune

I have tested the script and corrected a couple of bugs.
The correct script is:

N=33;
x = reshape(sin((0:N-1)*0.2*pi),N,1);
M = 512;
y = 0.5*randn(M,1);
K = 128;
y(K:K+N-1)=y(K:K+N-1)+x;
% cxy = crosscorr(y,x);   % Home-made cross correlation routine
%=====================
cxy =xcorr(x,y);
cxy =xcorr(y,x);
%=====================
kv=(1:N+M-1)-N;
plot(kv,cxy);
xlabel('Lag k')

I don't have the SP toolbox, so I don't know which of
the xcorr statements is the correct one, but one of them
gives a peak at k = 128.

Rune

>I have tested the script and corrected a couple of bugs.
>The correct script is:
>
>N=33;
>x = reshape(sin((0:N-1)*0.2*pi),N,1);
>M = 512;
>y = 0.5*randn(M,1);
>K = 128;
>y(K:K+N-1)=y(K:K+N-1)+x;
>% cxy = crosscorr(y,x);   % Home-made cross correlation routine
>%=====================
>cxy =xcorr(x,y);
>cxy =xcorr(y,x);
>%=====================
>kv=(1:N+M-1)-N;
>plot(kv,cxy);
>xlabel('Lag k')
>
>I don't have the SP toolbox, so I don't know which of
>the xcorr statements is the correct one, but one of them
>gives a peak at k = 128.
>
>Rune
>

Hi Rune,
Did exactly as above and still get the error
??? Error using ==> plot
Vectors must be the same lengths.

I think the length of the x and y axis need to be the same
regards
John

On 6 Feb, 20:52, "john1985" <murray_1...@hotmail.com> wrote:
> >I have tested the script and corrected a couple of bugs.
> >The correct script is:
>
> >N=33;
> >x = reshape(sin((0:N-1)*0.2*pi),N,1);
> >M = 512;
> >y = 0.5*randn(M,1);
> >K = 128;
> >y(K:K+N-1)=y(K:K+N-1)+x;
> >% cxy = crosscorr(y,x); &#4294967295; % Home-made cross correlation routine
> >%=====================
> >cxy =xcorr(x,y);
> >cxy =xcorr(y,x);
> >%=====================
> >kv=(1:N+M-1)-N;
> >plot(kv,cxy);
> >xlabel('Lag k')
>
> >I don't have the SP toolbox, so I don't know which of
> >the xcorr statements is the correct one, but one of them
> >gives a peak at k = 128.
>
> >Rune
>
> Hi Rune,
> Did exactly as above and still get the error
> ??? Error using ==> plot
> Vectors must be the same lengths.
>
> I think the length of the x and y axis need to be the same
> regards

I checked the dosumentation of xcorr, and it says

"c = xcorr(x,y) returns the cross-correlation sequence in
a length 2*N-1 vector, where x and y are length N vectors
(N>1). If x and y are not the same length, the shorter vector
is zero-padded to the length of the longer vector."

I find it counterintuitive to do things that way but...
anyway, in that case it seems the line

kv = ...

above should be changed to

N=max(length(x),length(y));
kv= (1:2*N-1)-N;

Rune