A zombie attack modeled in Python.

Python 2 (2.7 or above), NumPy, SciPy, matplotlib

The program consists of one Python file, zombies.py. It can be run from a Unix command line using:

python zombies.py

The program consists of three different models for a zombie attack: a basic model, a model with a latent period in which humans are infected but not zombies, and a model with treatment for zombie-ism.

The function basic_zombies(y, t, Alpha, Beta, Delta, Pi, Zeta) returns a derivative for the vector y at time t; this can be passed into scipy.integrate.odeint() to solve the set of ODEs that represent the basic model. The functions latent_period(y, t, Alpha, Beta, Delta, Pi, Roh, Zeta) and treatment(y, t, Alpha, Beta, c, Delta, Pi, Roh, Zeta) do the same task for the two other models.

For the basic model, the vector y consists of [S, Z, R], where S stands for Susceptibles (humans who are not yet zombies but could be), Z stands for Zombies, and R stands for Removed (humans who have died, either through attacks or natural causes.) For the other two models, y consists of [S, I, Z, R]; S, Z and R are same as before, and I stands for Infected (humans who have been bitten by a zombie but are not yet zombies).

Alpha, Beta, c, Delta, Pi, Roh, Zeta are all constants in the ODEs. These represent the following:

Alpha -- the rate at which a susceptible can resist becoming a zombie by fighting zombies off Beta -- the rate at which a susceptible becomes a zombie via transmission c -- rate of cure from zombie-ism Delta -- rate of natural (non-zombie-related) death Pi -- birth rate Roh -- rate at which an infected person becomes a zombie Zeta -- rate at which humans in the removed class resurrect and become zombies

The run_basic(), run_latent(), and run_treatment() functions all solve the respective ODEs using scipy.integrate.odeint() and plot the results using matplotlib.pyplot. Currently, the solutions for Susceptibles and Zombies are plotted. The solution for the Removed and Infected classes can be plotted using the correct indices in the solution variable.

The values used by the constants are set in the following piece of code:

if __name__ == '__main__':
    Alpha, Beta, c, Delta, Pi, Roh, Zeta = 0.005, 0.0028, 0.05, 0.0001, 0, 5, 5

These values can be changed and the modified values will be passed into the three run() functions.

Each of the three run() functions have initial values in a variable called init and the time range (start time, end time, and time step) in a variable called times. The values there can be changed to modify the initial conditions and time ranges. Currently, initial values are set to 500 (thousand) for Susceptibles, and zero for the others. times is (0, 20, 100).