#!/usr/bin/python

# 7.2

import os, sys

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

import pylab as pl

from scipy import signal

from bode import freqresp, phasemag

# def freqresp(H, omega):

#     num = pl.poly1d(H.num)

#     den = pl.poly1d(H.den)

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

#     fresp = pl.array(fresp)

#     mag = pl.absolute(fresp)

#     phase = pl.angle(fresp)

#     return mag, phase, omega

def nyquist(sys, omega=None):

    if (omega == None):

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

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

    x = pl.real(fresp)

    y = pl.imag(fresp)

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

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

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

    pl.show()

num = [1]

den = [1, -1, 0]

H = signal.lti(num, den)

nyquist(H)