2.2.py

#!/usr/bin/env python

####################################################################
###    This is the PYTHON version of program 2.2 from page 27 of   #
### "Modeling Infectious Disease in humans and animals"            #
### by Keeling & Rohani.				           #
### It is the simple SIR epidemic with equal births and deaths.    #
####################################################################

###################################
### Written by Ilias Soumpasis    #
### ilias.soumpasis@ucd.ie (work) #
### ilias.soumpasis@gmail.com	  #
###################################

import scipy.integrate as spi
import numpy as np
import pylab as pl

mu=1/(70*365.0)
beta=520/365.0
gamma=1/7.0
TS=1.0
ND=60*365
S0=0.1
I0=1e-4
R0=1-S0-I0
INPUT = (S0, I0, R0)

def diff_eqs(INP,t):  
	'''The main set of equations'''
	Y=np.zeros((3))
	V = INP    
	Y[0] = mu - beta * V[0] * V[1] - mu * V[0]
	Y[1] = beta * V[0] * V[1] - gamma * V[1] - mu * V[1]
	Y[2] = gamma * V[1] - mu * V[2]
	return Y   # For odeint



t_start = 0.0; t_end = ND; t_inc = TS
t_range = np.arange(t_start, t_end+t_inc, t_inc)
RES = spi.odeint(diff_eqs,INPUT,t_range)

print RES

#Ploting
pl.subplot(311)
pl.plot(RES[:,0], '-g', label='Susceptibles')
pl.title('Program_2_2.py')
pl.xlabel('Time')
pl.ylabel('Susceptibles')
pl.subplot(312)
pl.plot(RES[:,1], '-r', label='Infectious')
pl.xlabel('Time')
pl.ylabel('Infectious')
pl.subplot(313)
pl.plot(RES[:,2], '-k', label='Recovereds')
pl.xlabel('Time')
pl.ylabel('Recovereds')
pl.show()