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
|
/*
* 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.math3.genetics;
/**
* Individual in a population. Chromosomes are compared based on their fitness.
*
* <p>The chromosomes are IMMUTABLE, and so their fitness is also immutable and therefore it can be
* cached.
*
* @since 2.0
*/
public abstract class Chromosome implements Comparable<Chromosome>, Fitness {
/** Value assigned when no fitness has been computed yet. */
private static final double NO_FITNESS = Double.NEGATIVE_INFINITY;
/** Cached value of the fitness of this chromosome. */
private double fitness = NO_FITNESS;
/**
* Access the fitness of this chromosome. The bigger the fitness, the better the chromosome.
*
* <p>Computation of fitness is usually very time-consuming task, therefore the fitness is
* cached.
*
* @return the fitness
*/
public double getFitness() {
if (this.fitness == NO_FITNESS) {
// no cache - compute the fitness
this.fitness = fitness();
}
return this.fitness;
}
/**
* Compares two chromosomes based on their fitness. The bigger the fitness, the better the
* chromosome.
*
* @param another another chromosome to compare
* @return
* <ul>
* <li>-1 if <code>another</code> is better than <code>this</code>
* <li>1 if <code>another</code> is worse than <code>this</code>
* <li>0 if the two chromosomes have the same fitness
* </ul>
*/
public int compareTo(final Chromosome another) {
return Double.compare(getFitness(), another.getFitness());
}
/**
* Returns <code>true</code> iff <code>another</code> has the same representation and therefore
* the same fitness. By default, it returns false -- override it in your implementation if you
* need it.
*
* @param another chromosome to compare
* @return true if <code>another</code> is equivalent to this chromosome
*/
protected boolean isSame(final Chromosome another) {
return false;
}
/**
* Searches the <code>population</code> for another chromosome with the same representation. If
* such chromosome is found, it is returned, if no such chromosome exists, returns <code>null
* </code>.
*
* @param population Population to search
* @return Chromosome with the same representation, or <code>null</code> if no such chromosome
* exists.
*/
protected Chromosome findSameChromosome(final Population population) {
for (Chromosome anotherChr : population) {
if (this.isSame(anotherChr)) {
return anotherChr;
}
}
return null;
}
/**
* Searches the population for a chromosome representing the same solution, and if it finds one,
* updates the fitness to its value.
*
* @param population Population to search
*/
public void searchForFitnessUpdate(final Population population) {
Chromosome sameChromosome = findSameChromosome(population);
if (sameChromosome != null) {
fitness = sameChromosome.getFitness();
}
}
}
|
