1 """General functionality for crossover that doesn't apply.
2
3 This collects Crossover stuff that doesn't deal with any specific
4 type of crossover.
5 """
6
7 import random
8
9
10 from Bio.GA.Organism import Organism
11
13 """Perform crossovers, but do not allow decreases in organism fitness.
14
15 This doesn't actually do any crossover work, but instead relies on
16 another class to do the crossover and just checks that newly created
17 organisms do not have less fitness. This is useful for cases where
18 crossovers can
19 """
20 - def __init__(self, actual_crossover, accept_less = 0.0):
21 """Initialize to do safe crossovers.
22
23 Arguments:
24
25 o actual_crossover - A Crossover class which actually implements
26 crossover functionality.
27
28 o accept_less - A probability to accept crossovers which
29 generate less fitness. This allows you to accept some
30 crossovers which reduce fitness, but not all of them.
31 """
32 self._crossover = actual_crossover
33 self._accept_less_percent = accept_less
34 self._accept_less_rand = random.Random()
35
37 """Perform a safe crossover between the two organism.
38 """
39 new_org_1, new_org_2 = self._crossover.do_crossover(org_1, org_2)
40
41 return_orgs = []
42
43 for start_org, new_org in ((org_1, new_org_1),
44 (org_2, new_org_2)):
45 new_org.recalculate_fitness()
46
47
48
49 if start_org.fitness > new_org.fitness:
50 accept_change = self._accept_less_rand.random()
51 if accept_change <= self._accept_less_percent:
52 return_orgs.append(new_org)
53 else:
54 return_orgs.append(start_org)
55 else:
56 return_orgs.append(new_org)
57
58 assert len(return_orgs) == 2, "Should have two organisms to return."
59
60 return return_orgs
61