Generates the initial population and assigns fitnesses.

def initialize_pop(self):
        """Generates the initial population and assigns fitnesses."""
        self.initialize_cma_es(
            sigma=self._params['sigma'], weights=self._params['weights'],
            lambda_=self._params['popsize'],
            centroid=[0] * len(self._params['value_means']))
        self.toolbox.register("individual", self.make_individual)
        self.toolbox.register("generate", self.generate,
                              self.toolbox.individual)
        self.toolbox.register("population", tools.initRepeat,
                              list, self.initial_individual)
        self.toolbox.register("update", self.update)
        self.population = self.toolbox.population(n=self._params['popsize'])
        self.assign_fitnesses(self.population)
        self._params['model_count'] += len(self.population)