blob: f1a091fc41cdfd7556cec47834c3103d9bfd3037 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
|
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.math.genetics;
import java.util.ArrayList;
import java.util.List;
/**
* Tournament selection scheme. Each of the two selected chromosomes is selected
* based on n-ary tournament -- this is done by drawing {@link #arity} random
* chromosomes without replacement from the population, and then selecting the
* fittest chromosome among them.
*
* @since 2.0
* @version $Revision: 811685 $ $Date: 2009-09-05 19:36:48 +0200 (sam. 05 sept. 2009) $
*/
public class TournamentSelection implements SelectionPolicy {
/** number of chromosomes included in the tournament selections */
private int arity;
/**
* Creates a new TournamentSelection instance.
*
* @param arity
* how many chromosomes will be drawn to the tournament
*/
public TournamentSelection(int arity) {
this.arity = arity;
}
/**
* Select two chromosomes from the population. Each of the two selected
* chromosomes is selected based on n-ary tournament -- this is done by
* drawing {@link #arity} random chromosomes without replacement from the
* population, and then selecting the fittest chromosome among them.
*
* @param population
* the population from which the chromosomes are choosen.
* @return the selected chromosomes.
*/
public ChromosomePair select(Population population) {
return new ChromosomePair(
tournament((ListPopulation) population),
tournament((ListPopulation)population)
);
}
/**
* Helper for {@link #select(Population)}. Draw {@link #arity} random
* chromosomes without replacement from the population, and then select the
* fittest chromosome among them.
*
* @param population
* the population from which the chromosomes are choosen.
* @return the selected chromosome.
*/
private Chromosome tournament(ListPopulation population) {
if (population.getPopulationSize() < this.arity)
throw new IllegalArgumentException("Tournament arity cannot be bigger than population size.");
// auxiliary population
ListPopulation tournamentPopulation = new ListPopulation(this.arity) {
public Population nextGeneration() {
// not useful here
return null;
}
};
// create a copy of the chromosome list
List<Chromosome> chromosomes = new ArrayList<Chromosome> (population.getChromosomes());
for (int i=0; i<this.arity; i++) {
// select a random individual and add it to the tournament
int rind = GeneticAlgorithm.getRandomGenerator().nextInt(chromosomes.size());
tournamentPopulation.addChromosome(chromosomes.get(rind));
// do not select it again
chromosomes.remove(rind);
}
// the winner takes it all
return tournamentPopulation.getFittestChromosome();
}
/**
* Gets the arity (number of chromosomes drawn to the tournament).
*
* @return arity of the tournament
*/
public int getArity() {
return arity;
}
/**
* Sets the arity (number of chromosomes drawn to the tournament).
*
* @param arity arity of the tournament
*/
public void setArity(int arity) {
this.arity = arity;
}
}
|
