; This batch file computes the coefficients of a discrete transfer
; function used in the Infinite Impulse Respose filter example from
; Chapter 13, "Signal Processing", of _Using IDL_.

delt = 0.02
f0 = 6.5 ; notch frequency in cycles / second
C = (1.0-!PI*f0*delt) / (1.0+!PI*f0*delt)
B = [(1+C^2)/2, -2*C, (1+C^2)/2]
A = [   C^2,    -2*C,     1    ]