; This batch file creates a plot of the power spectrum of 
; the simulated signal used in the example from Chapter 13,
; "Signal Processing", of _Using IDL_, with a 30 cycle/second
; periodic component added.

@sigprc01  ; compute time data sequence u

F = FINDGEN(N/2+1) / (N*delt) ; f = [0.0, 1.0/(N*delt), ... , 1.0/(2.0*delt)]

u_a = U + SIN(2*!PI*30.0*delt*FINDGEN(N))

v_a = FFT(u_a)

; log-log plot of power spectrum

PLOT, F, ABS(v_a(0:N/2))^2, YTITLE='Power Spectrum', $
    /YLOG, YRANGE=[1.0e-8,1.0], YSTYLE=1, YMARGIN=[4,4], $
    XTITLE='Frequency in cycles / second', $
    /XLOG, XRANGE=[1.0,1.0/(2.0*delt)], XSTYLE=1, $
    TITLE='Power Spectrum with (solid) and without!C(dashed) Aliased 30 c/s Component'

OPLOT, F, ABS((FFT(U))(0:N/2))^2, LINESTYLE=2 ; overplot without window