1 #!/usr/bin/python

     2 ## 4.11

     3 

     4 import scipy as sp

     5 from scipy import signal

     6 

     7 num = sp.array([11,-15,6])

     8 den = signal.convolve([1,-2],signal.convolve([1,-1],[1,-1]))

     9 u = sp.zeros(5)

    10 u[0] = 1

    11 y = signal.lfilter(num,den,u)

    12 

    13 print num, den

    14 

    15 #Plot of impulse response???