hi!
I need to calculate the autocorrelation function "g" of some signal
"S", the latter being vector with N elements. I did:
lag = indgen( N )
g = a_correlate( S, lag )
This works fine for relatively small N, but above ~ 4,000,000 it says
something like:
subscript of S : low>0, high<N-1 etc.....
I cannot see in a_correlate.pro why it does this.
I have also tried using the FFT which a lot faster and looks good but
somehow the normalisation is not the same. This all might be simple but
I am useless with discrete fourier transform. :)
Any suggestions??
Thanx
Yves.
