001 /*
002 * Java Genetic Algorithm Library (jenetics-3.9.0).
003 * Copyright (c) 2007-2017 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@gmx.at)
019 */
020 package org.jenetics.prog.op;
021
022 import static java.util.Objects.requireNonNull;
023
024 /**
025 * Represents the program variables. The {@code Var} operation is a termination
026 * operation, which just returns the value with the defined index of the input
027 * variable array. It is essentially an orthogonal projection of the
028 * <em>n</em>-dimensional input space to the <em>1</em>-dimensional result space.
029 *
030 * <pre>{@code
031 * final ISeq<? extends Op<Double>> operations = ISeq.of(...);
032 * final ISeq<? extends Op<Double>> terminals = ISeq.of(
033 * Var.of("x", 0), Var.of("y", 1)
034 * );
035 * }</pre>
036 *
037 * The example above shows how to define the terminal operations for a GP, which
038 * tries to optimize a 2-dimensional function.
039 *
040 * <pre>{@code
041 * static double error(final ProgramChromosome<Double> program) {
042 * final double x = ...;
043 * final double y = ...;
044 * final double result = program.apply(x, y);
045 * ...
046 *
047 * return ...;
048 * }
049 * }</pre>
050 *
051 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
052 * @version 3.9
053 * @since 3.9
054 */
055 public final class Var<T> implements Op<T> {
056
057 private final String _name;
058 private final int _index;
059
060 /**
061 * Create a new variable with the given {@code name} and projection
062 * {@code index}.
063 *
064 * @param name the variable name. Used when printing the operation tree
065 * (program)
066 * @param index the projection index
067 * @throws IllegalArgumentException if the projection {@code index} is
068 * smaller than zero
069 * @throws NullPointerException if the given variable {@code name} is
070 * {@code null}
071 */
072 private Var(final String name, final int index) {
073 _name = requireNonNull(name);
074 if (index < 0) {
075 throw new IndexOutOfBoundsException(
076 "Index smaller than zero: " + index
077 );
078 }
079 _index = index;
080 }
081
082 /**
083 * The projection index of the variable.
084 *
085 * @return the projection index of the variable
086 */
087 public int index() {
088 return _index;
089 }
090
091 @Override
092 public String name() {
093 return _name;
094 }
095
096 @Override
097 public int arity() {
098 return 0;
099 }
100
101 @Override
102 public T apply(final T[] variables) {
103 return variables[_index];
104 }
105
106 @Override
107 public int hashCode() {
108 int hash = 17;
109 hash += 31*_name.hashCode() + 37;
110 hash += 31*_index + 37;
111 return hash;
112 }
113
114 @Override
115 public boolean equals(final Object obj) {
116 return obj instanceof Var<?> &&
117 ((Var)obj)._name.equals(_name) &&
118 ((Var)obj)._index == _index;
119 }
120
121 @Override
122 public String toString() {
123 return _name;
124 }
125
126 /**
127 * Create a new variable with the given {@code name} and projection
128 * {@code index}.
129 *
130 * @param name the variable name. Used when printing the operation tree
131 * (program)
132 * @param index the projection index
133 * @param <T> the variable type
134 * @return a new variable with the given {@code name} and projection
135 * {@code index}
136 */
137 public static <T> Var<T> of(final String name, final int index) {
138 return new Var<>(name, index);
139 }
140
141 }
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