14.7. The Simulation

The Simulation class for this chapter is based on the one in Section 13.5; the only differences are in __init__ and step.

Here’s the __init__ method:

class PDSimulation(Simulation):

    def __init__(self, tournament, agents):
        self.tournament = tournament
        self.agents = np.asarray(agents)
        self.instruments = []

A Simulation object contains a Tournament object, a sequence of agents, and a sequence of Instrument objects (as in Section 13.7).

Here’s the step method:

def step(self):

This version of step USES Tournament.melee, which sets the fitness attribute for each agent; then it calls the step method from the Simulation class, reproduced here:

# class Simulation

    def step(self):
        n = len(self.agents)
        fits = self.get_fitnesses()

        # see who dies
        index_dead = self.choose_dead(fits)
        num_dead = len(index_dead)

        # replace the dead with copies of the living
        replacements = self.choose_replacements(num_dead, fits)
        self.agents[index_dead] = replacements

        # update any instruments

Simulation.step collects the agents’ fitnesses in an array; then it calls choose_dead to decide which agents die, and choose_replacements to decide which agents reproduce.

The provided simulation includes differential survival, as in Section 13.8, but not differential reproduction. You can see the details in the notebook for this chapter. As one of the exercises, you will have a chance to explore the effect of differential reproduction.

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