"""Keeps track of whether species are making progress and helps remove those which are not."""
import sys
from neat.config import ConfigParameter, DefaultClassConfig
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 species_set.species.items():
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