; This batch file creates a plot of the real and imaginary parts
; of the simulated signal used in the example from Chapter 13,
; "Signal Processing", of _Using IDL_.

@sigprc01  ; compute time data sequence u

V = FFT(U) ; compute spectrum v

M = (INDGEN(N)-(N/2-1)) ; m = [-(N/2-1), ... , -1, 0, 1, ... , N/2-1, N/2]

F = M / (N*delt)        ; frequencies corresponding to m in cycles/second

!P.MULTI = [0, 1, 2] ; set up for two plots in window

PLOT, F, FLOAT(SHIFT(V,N/2-1)), $
      YTITLE='real part of spectrum', $
      XTITLE='Frequency in cycles / second', $
      XRANGE=[-1,1]/(2*delt), XSTYLE=1, $
      TITLE='Spectrum of u(k)'

PLOT, F, IMAGINARY(SHIFT(V,N/2-1)), $
      YTITLE='imaginary part of spectrum', $
      XTITLE='Frequency in cycles / second', $
      XRANGE=[-1,1]/(2*delt), XSTYLE=1

!P.MULTI = 0