usage()
        sys.exit()
    elif option in ("-a", "--prey-birth"):
        prey_birth = float(argument)
    elif option in ("-b", "--prey-death"):
        prey_death = float(argument)
    elif option in ("-c", "--predator-death"):
        predator_death = float(argument)
    elif option in ("-d", "--predator-birth"):
        predator_birth = float(argument)
    elif option in ("-f", "--num-predators"):
        num_predators = float(argument)
    elif option in ("-r", "--num-prey"):
        num_prey = float(argument)
    elif option in ("-t", "--time"):
        time = float(argument)
    elif option in ("-n", "--time-steps"):
        time_steps = float(argument)

predator_config = {}
predator_config[BIRTH] = predator_birth
predator_config[DEATH] = predator_death
predator_config[POPULATION] = num_predators
prey_config = {}
prey_config[BIRTH] = prey_birth
prey_config[DEATH] = prey_death
prey_config[POPULATION] = num_prey

results = simulate(prey_config, predator_config, time, time_steps)
plot(results)
import sys

import numpy as np

from lotkavolterra import plot

def usage():
    '''Print usage information.'''
    print "Usage: python plot_lv.py DATA_FILE"
    print "View the results of a simulation of the evolution of a population of predators and prey using the Lotka-Volterra equations."
    print "This program inputs a CSV file with the time, prey population and predator population at each time-step"

if len(sys.argv) < 2:
    usage()
    sys.exit()
else:
    data_file = sys.argv[1]

data = np.loadtxt(data_file, delimiter=",")
plot(data)