ds-phasespace-drawing-exercise.py

from pylab import *

def initialize(x0, y0):
    global x, y, xresult, yresult
    x = x0
    y = y0
    xresult = [x]
    yresult = [y]

def observe():
    global x, y, xresult, yresult
    xresult.append(x)
    yresult.append(y)

def update():
    global x, y, xresult, yresult
    nextx = x + 0.1 * (x - x * y)
    nexty = y + 0.1 * (y - x * y)
    x, y = nextx, nexty

for x0 in arange(0, 2, .1):
    for y0 in arange(0, 2, .1):
        initialize(x0, y0)
        for t in range(30):
            update()
            observe()
        plot(xresult, yresult, 'b')

axis([0, 2, 0, 2]) ### added to zoom in the area within which
                   ### initial states were varied
show()