Introduction to the Modeling and Analysis of Complex Systems

19.4. ECOLOGICAL AND EVOLUTIONARY MODELS 453nr = 500. # carrying capacity of rabbitsr_init = 100 # initial rabbit populationmr = 0.03 # magnitude of movement of rabbitsdr = 1.0 # death rate of rabbits when it faces foxesrr = 0.1 # reproduction rate of rabbitsf_init = 30 # initial fox populationmf = 0.05 # magnitude of movement of foxesdf = 0.1 # death rate of foxes when there is no foodrf = 0.5 # reproduction rate of foxescd = 0.02 # radius for collision detectioncdsq = cd ** 2class agent:passdef initialize():global agentsagents = []for i in xrange(r_init + f_init):ag = agent()ag.type = ’r’ if i < r_init else ’f’ag.x = random()ag.y = random()agents.append(ag)def observe():global agentscla()rabbits = [ag for ag in agents if ag.type == ’r’]if len(rabbits) > 0:x = [ag.x for ag in rabbits]y = [ag.y for ag in rabbits]plot(x, y, ’b.’)