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i didn't get the question !

how can i matlab this !

We may model the evolution of an epidemic in a fixed population by dividing the population into three classes 1. S: Susceptibles, those who have never had the illness and can catch it 2. I: Infectives, those who are infected and are contagious 3. R: Recovered, those who already had the illness and are immune We assume the disease is mild enough that everyone eventually recovers, that the disease confers permanent immunity on those who have recovered, and that those with the disease are infective until they recover. For the examples in this class we'll assume the unit of time is one day; We can model how the disease moves through the population over time given a couple variables a is the contact rate, ie, the average number of people a person comes in contact with b is the amount of time (in days) that a person is infectious We can model what happens over time using ordinary differential equations - these are equations that say how a given value (eg, S, I, and R) change if you take a small step forward in time (very similar to the Euler leaf problem, where the position changes based on the velocity). The total population is N = S+I+R. Assume no births or deaths, so N always stays the same How S changes: How s changes:-=- dt dI aSl =--1/b dR How l changes: dt . How R changes: An epidemic is defined by more people being infected each day than recover each day. For the following, let a = 10 and b = 1.25. The starting value for R is always 0 (no one's recovered yet). The starting value of I is 100 (100 people have been infected). Starting values for S will vary