Epidemien - SIR model without vital dynamics
        Blue: Susceptible population rate
        Red: Infected population rate
        Green: Recovered population rate (which means: immune, isolated or dead)
        
        
        
        
        Hong Kong flu: initially 7.9 million people, 10 infected, 0 recovered. Thus S(0) = 1, I(0) = 1.27E-6, R(0) = 0, see http://www.cs.princeton.edu/introcs/94diffeq/.