How to Calculate Continuous Spectrum
			q There are two ways to calculate the continuous spectrum: (1) (1) Direct Method  (use Fourier transform) (2) (2) Time-Lag Correlation Method (use autocorrelation function)
		(1) Direct Method (a more popular method)      Step 1: Perform Fourier transform of y(t) to get C2(k)      Step 2: smooth C2(k) by averaging a few adjacent frequencies together.                   or by averaging the spectra of a few time series together.     è both ways smooth a line spectrum to a continuous spectrum and          increase the degrees of freedom of the spectrum.