... One of the most widely used tools of Fourier analysis is the Parseval theorem. It enables the experimentalist to view how the `energy' in the signal is distributed among frequencies. The Fast Fourier Transform (FFT) algorithms have made power spectra one of the obvious diagnostics tools during data acquisition, and energy maps are a versatile alternative. ... The result is an energy map (Fig. 9), showing the distribution of energy corresponding to the wavelet map (Fig. ...