eckity.multi_objective_evolution.nsga2_breeder

 1from eckity.breeders.simple_breeder import SimpleBreeder
 2from eckity.genetic_operators.selections.elitism_selection import ElitismSelection
 3
 4
 5class NSGA2Breeder(SimpleBreeder):
 6	def __init__(self,
 7				 events=None):
 8		super().__init__(events=events)
 9		self.selected_individuals = []  # TODO why do we need this field? what about applied_individuals?
10
11	def apply_breed(self, population):
12		"""
13        Apply elitism, selection method and the sub-population's operator sequence on each sub-population.
14        In simple case, the operator sequence is applied on the one and only sub-population.
15
16        adds the current generation to the next generation
17
18        Parameters
19        ----------
20        population:
21            Population of sub-populations of individuals. The operators will be applied on those individuals.
22
23        Returns
24        -------
25        None.
26        """
27		for subpopulation in population.sub_populations:
28			nextgen_population = []
29
30			num_elites = subpopulation.n_elite
31			if num_elites > 0:
32				elitism_sel = ElitismSelection(num_elites=num_elites, higher_is_better=subpopulation.higher_is_better)
33				elitism_sel.apply_operator((subpopulation.individuals, nextgen_population))
34
35			nextgen_population = self._create_next_gen(subpopulation)
36
37			self.selected_individuals = subpopulation.get_selection_methods()[0][0] \
38				.select(subpopulation.individuals, nextgen_population)
39
40			subpopulation.individuals = nextgen_population
41
42	def _create_next_gen(self, subpopulation):
43		# oldgen_population = deepcopy(subpopulation.individuals)  # needed since apply operator changes the values of
44		oldgen_population = [ind.clone() for ind in subpopulation.individuals]
45
46		nextgen_population = self._apply_operators(subpopulation.get_operators_sequence(),
47												   subpopulation.individuals)  # self.selected_individuals)
48
49		oldgen_population += nextgen_population
50		nextgen_population = oldgen_population
51
52		for ind in nextgen_population:
53			ind.fitness.set_not_evaluated()
54
55		return nextgen_population