Time-Lag Correlation Method
	(2) Time-Lag Correlation Method       It can be shown that the autocorrelation function and power spectrum are Fourier transform of each other. So we can obtain the continuous spectrum by by performing harmonic analysis on the lag correlation function on the interval -TL £ t £ TL.
					F(k): Power Spectrum in frequency (k)   r(t): Autocorrelation in time lag (t)