An outbreak of a disease is represented by the SIR model, where the variables are S: Number of susceptible people, who are currently healthy but could get the disease. I: Number of infected people R: Number of people who have recovered The variables are related by the following equations for positive constants a and b, S' = -aSI I' = aSI - bI R' = bI For a particular epidemic which ran for 60 days, the time series for the susceptible and infected populations are given in these graphs. Initially at time t = 0, no one has recovered. susceptibles infecteds 4000 1000 3000 800 600 2000 400 1000 200 0 time (days) 0 time (days) 10 20 30 40 50 60 10 20 30 40 50 60