eckity.creators.gp_creators.grow

 1from random import random
 2
 3from overrides import overrides
 4
 5from eckity.creators.gp_creators.tree_creator import GPTreeCreator
 6
 7
 8class GrowCreator(GPTreeCreator):
 9	def __init__(self,
10				 init_depth=None,
11				 function_set=None,
12				 terminal_set=None,
13				 erc_range=None,
14				 bloat_weight=0.1,
15				 events=None):
16		"""
17		Tree creator using the grow method
18
19		Parameters
20		----------
21		init_depth : (int, int)
22		Min and max depths of initial random trees. The default is None.
23
24		function_set : list
25			List of functions used as internal nodes in the GP-tree. The default is None.
26
27		terminal_set : list
28			List of terminals used in the GP-tree leaves. The default is None.
29
30		erc_range : (float, float)
31			Range of values for ephemeral random constant (ERC). The default is None.
32
33		bloat_weight : float
34			Bloat control weight to punish large trees. Bigger values make a bigger punish.
35
36		events : list
37			List of events related to this class
38		"""
39		super().__init__(init_depth=init_depth, function_set=function_set, terminal_set=terminal_set,
40						 erc_range=erc_range, bloat_weight=bloat_weight, events=events)
41
42	@overrides
43	def create_tree(self, tree_ind, max_depth=5):
44		"""
45		Create a random tree using the grow method, and assign it to the given individual.
46
47		Parameters
48		----------
49		tree_ind: Tree
50			An individual of GP Tree representation with an initially empty tree
51
52		max_depth: int
53			Maximum depth of tree. The default is 5.
54
55		Returns
56		-------
57		None.
58		"""
59		self._create_tree(tree_ind, max_depth, 0)
60
61	def _create_tree(self, tree_ind, max_depth=5, depth=0):
62		"""
63		Recursively create a random tree using the grow method
64
65		Parameters
66		----------
67		max_depth : int
68			Maximum depth of tree. The default is 2.
69		depth : int, optional
70			Current depth in recursive process. The default is 0.
71
72		Returns
73		-------
74		None.
75
76		"""
77		is_func = False
78
79		if depth < self.init_depth[0]:
80			node = tree_ind.random_function()
81			is_func = True
82		elif depth >= max_depth:
83			node = tree_ind.random_terminal()
84		else:  # intermediate depth, grow
85			if random() > 0.5:
86				node = tree_ind.random_function()
87				is_func = True
88			else:
89				node = tree_ind.random_terminal()
90
91		# add the new node to the tree of the given individual
92		tree_ind.add_tree(node)
93
94		if is_func:
95			# recursively add arguments to the function node, according to its arity
96			for i in range(tree_ind.arity[node]):
97				self._create_tree(tree_ind, max_depth, depth=depth + 1)