001 /*
002 * Java Genetic Algorithm Library (jenetics-4.3.0).
003 * Copyright (c) 2007-2018 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 * Author:
018 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020 package io.jenetics.prog.op;
021
022 import static java.util.Objects.requireNonNull;
023 import static io.jenetics.internal.util.Hashes.hash;
024
025 import java.io.Serializable;
026 import java.util.Objects;
027
028 /**
029 * Represents the program variables. The {@code Var} operation is a termination
030 * operation, which just returns the value with the defined index of the input
031 * variable array. It is essentially an orthogonal projection of the
032 * <em>n</em>-dimensional input space to the <em>1</em>-dimensional result space.
033 *
034 * <pre>{@code
035 * final ISeq<? extends Op<Double>> operations = ISeq.of(...);
036 * final ISeq<? extends Op<Double>> terminals = ISeq.of(
037 * Var.of("x", 0), Var.of("y", 1)
038 * );
039 * }</pre>
040 *
041 * The example above shows how to define the terminal operations for a GP, which
042 * tries to optimize a 2-dimensional function.
043 *
044 * <pre>{@code
045 * static double error(final ProgramChromosome<Double> program) {
046 * final double x = ...;
047 * final double y = ...;
048 * final double result = program.apply(x, y);
049 * ...
050 *
051 * return ...;
052 * }
053 * }</pre>
054 *
055 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
056 * @version 4.1
057 * @since 3.9
058 */
059 public final class Var<T> implements Op<T>, Serializable {
060
061 private static final long serialVersionUID = 1L;
062
063 private final String _name;
064 private final int _index;
065
066 /**
067 * Create a new variable with the given {@code name} and projection
068 * {@code index}.
069 *
070 * @param name the variable name. Used when printing the operation tree
071 * (program)
072 * @param index the projection index
073 * @throws IllegalArgumentException if the projection {@code index} is
074 * smaller than zero
075 * @throws NullPointerException if the given variable {@code name} is
076 * {@code null}
077 */
078 private Var(final String name, final int index) {
079 _name = requireNonNull(name);
080 if (index < 0) {
081 throw new IndexOutOfBoundsException(
082 "Index smaller than zero: " + index
083 );
084 }
085 _index = index;
086 }
087
088 /**
089 * The projection index of the variable.
090 *
091 * @return the projection index of the variable
092 */
093 public int index() {
094 return _index;
095 }
096
097 @Override
098 public String name() {
099 return _name;
100 }
101
102 @Override
103 public int arity() {
104 return 0;
105 }
106
107 @Override
108 public T apply(final T[] variables) {
109 return variables[_index];
110 }
111
112 @Override
113 public int hashCode() {
114 return hash(_name, hash(_index));
115 }
116
117 @Override
118 public boolean equals(final Object obj) {
119 return obj == this ||
120 obj instanceof Var &&
121 Objects.equals(((Var)obj)._name, _name) &&
122 ((Var)obj)._index == _index;
123 }
124
125 @Override
126 public String toString() {
127 return _name;
128 }
129
130 /**
131 * Create a new variable with the given {@code name} and projection
132 * {@code index}.
133 *
134 * @param name the variable name. Used when printing the operation tree
135 * (program)
136 * @param index the projection index
137 * @param <T> the variable type
138 * @return a new variable with the given {@code name} and projection
139 * {@code index}
140 */
141 public static <T> Var<T> of(final String name, final int index) {
142 return new Var<>(name, index);
143 }
144
145 }
|