1 #!/usr/bin/python

     2 # 7.2

     3 import os, sys

     4 sys.path += [os.getcwdu() + os.sep + ".." + os.sep + "python"]

     5 

     6 import pylab as pl

     7 from scipy import signal

     8 from bode import freqresp, phasemag

     9 

    10 

    11 # def freqresp(H, omega):

    12 #     num = pl.poly1d(H.num)

    13 #     den = pl.poly1d(H.den)

    14 

    15 #     fresp = map(lambda w: num(w*1j) / den(w*1j), omega)

    16 #     fresp = pl.array(fresp)

    17 #     mag = pl.absolute(fresp)

    18 #     phase = pl.angle(fresp)

    19 

    20 #     return mag, phase, omega

    21 

    22 def nyquist(sys, omega=None):

    23     if (omega == None):

    24         omega = pl.logspace(-2, 2, 5000)

    25 

    26     omega, fresp = freqresp(sys, omega, 'd')

    27 

    28     x = pl.real(fresp)

    29     y = pl.imag(fresp)

    30 

    31     pl.plot(x, y, '-');

    32     pl.plot(x, -y, '--');

    33 

    34     pl.plot([-1], [0], '+k')

    35 

    36     pl.show()

    37 

    38 num = [1]

    39 den = [1, -1, 0]

    40 H = signal.lti(num, den)

    41 

    42 nyquist(H)