Source code for stagnation

"""Keeps track of whether species are making progress and helps remove ones that are not."""
import sys

from neat.config import ConfigParameter, DefaultClassConfig
from neat.six_util import iteritems
from neat.math_util import stat_functions

# TODO: Add a method for the user to change the "is stagnant" computation.

[docs]class DefaultStagnation(DefaultClassConfig): """Keeps track of whether species are making progress and helps remove ones that are not."""
[docs] @classmethod def parse_config(cls, param_dict): return DefaultClassConfig(param_dict, [ConfigParameter('species_fitness_func', str, 'mean'), ConfigParameter('max_stagnation', int, 15), ConfigParameter('species_elitism', int, 0)])
def __init__(self, config, reporters): # pylint: disable=super-init-not-called self.stagnation_config = config self.species_fitness_func = stat_functions.get(config.species_fitness_func) if self.species_fitness_func is None: raise RuntimeError( "Unexpected species fitness func: {0!r}".format(config.species_fitness_func)) self.reporters = reporters
[docs] def update(self, species_set, generation): """ Required interface method. Updates species fitness history information, checking for ones that have not improved in max_stagnation generations, and - unless it would result in the number of species dropping below the configured species_elitism parameter if they were removed, in which case the highest-fitness species are spared - returns a list with stagnant species marked for removal. """ species_data = [] for sid, s in iteritems(species_set.species): if s.fitness_history: prev_fitness = max(s.fitness_history) else: prev_fitness = -sys.float_info.max s.fitness = self.species_fitness_func(s.get_fitnesses()) s.fitness_history.append(s.fitness) s.adjusted_fitness = None if prev_fitness is None or s.fitness > prev_fitness: s.last_improved = generation species_data.append((sid, s)) # Sort in ascending fitness order. species_data.sort(key=lambda x: x[1].fitness) result = [] species_fitnesses = [] num_non_stagnant = len(species_data) for idx, (sid, s) in enumerate(species_data): # Override stagnant state if marking this species as stagnant would # result in the total number of species dropping below the limit. # Because species are in ascending fitness order, less fit species # will be marked as stagnant first. stagnant_time = generation - s.last_improved is_stagnant = False if num_non_stagnant > self.stagnation_config.species_elitism: is_stagnant = stagnant_time >= self.stagnation_config.max_stagnation if (len(species_data) - idx) <= self.stagnation_config.species_elitism: is_stagnant = False if is_stagnant: num_non_stagnant -= 1 result.append((sid, s, is_stagnant)) species_fitnesses.append(s.fitness) return result