[Octave-bug-tracker] [bug #60076] [octave forge] (signal) xcorr bug for large datasets

[Mark van Rossum]

Follow-up Comment #5, bug #60076 (project octave):

Thank you Dmitri, I thought I was going crazy.
I see the bug on Ubuntu 20.04, but not on a different system with Debian 10.

Here is the core of the xcorr.m code.
  
%%%% xcorr.m code:
M = 2^nextpow2(N + maxlag)
post = fft( postpad(X(:),M) );
cor = ifft( post .* conj(post) );
R = [ conj(cor(maxlag+1:-1:2)) ; cor(1:maxlag+1) ];

Whenever the data length surpasses 4096, the ftt behaves oddly.
R gets large imaginary components, which should not happen.



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