Hello !
I test my project initially made for Matlab with Octave.
And I have a problem with the xcorr method.
the code :
a = [1 2 -1 -1]
b = [-1 1 2 -1 -1 1 2 -1]
round(xcorr(a,b))
return in matlab : -1 0 6 0 -6 0 7 0 -5
0 1 0 0 0 0
and in Octave : 0 -0 -0 0 -1 0 6 -0 -6 0 7 -0 -5 -0 1
than we see that there a shift problem, there is 4 0 after in matlab and
after in Octave.
In my project and in this example if I replace the xcorr with the method :
function [R, lags] = my_xcorr (X, Y)
N = max(length(X),length(Y))
maxlag=N-1
M = 2^nextpow2(N + maxlag)
%% compute cross-correlation of X and Y
post = fft (postpad(Y,M));
pre = fft (postpad(prepad(X,length(X)+maxlag),M));
cor = conj (ifft (conj(post(:)) .* pre(:)));
R = cor(1:2*maxlag+1);
if isreal(X) && (isempty(Y) || isreal(Y))
R=real(R);
end
if isvector(X)
R = R';
end
lags = [-maxlag:maxlag];
end
it will work great.
this method is the same as xcorr implementation (
http://octave.svn.sourceforge.net/viewvc/octave/trunk/octave-forge/main/signal/inst/xcorr.m?revision=HEAD&content-type=text/plain)
where I remove the code I don't need (but necessary ;-) ) an I replace the
line :
pre = fft (postpad(prepad(X,N+maxlag),M));
by
pre = fft (postpad(prepad(X,length(X)+maxlag),M));
Is it a good fix ? And can it be integrated in the next release of octave
forge ?
CU and thanks in advance.
Steph
--
Stéphane Brunner
mail : [EMAIL PROTECTED]
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