Specifying the InputStep 0 What about data? 
At this point, your model should look something like the figure below. Visually, you can see that susceptible people get sick and become infected people. The thin arching connector arrows suggest that this process is based on an infection fraction, the number of susceptible people, and the number of infected people. The framework for the model is now in place, but you haven't given it any data yet. Before simulating the model, you must define how many susceptible people and how many infected people there are when the model starts (at time zero). You must also construct a formula for how people get sick and specify the infection fraction. 

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