001 /*
002 * Java Genetic Algorithm Library (jenetics-6.1.0).
003 * Copyright (c) 2007-2020 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.regression;
021
022 import static java.util.Objects.requireNonNull;
023
024 import java.util.function.DoubleBinaryOperator;
025
026 import io.jenetics.ext.util.Tree;
027
028 import io.jenetics.prog.op.Op;
029
030 /**
031 * This function calculates the <em>overall</em> error of a given program tree.
032 * The error is calculated from the {@link LossFunction} and, if desired, the
033 * program {@link Complexity}.
034 *
035 * <pre>{@code
036 * final Error<Double> error = Error.of(LossFunction::mse, Complexity.ofNodeCount(50));
037 * }</pre>
038 *
039 * @see LossFunction
040 * @see Complexity
041 *
042 * @param <T> the sample type
043 *
044 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
045 * @version 5.0
046 * @since 5.0
047 */
048 @FunctionalInterface
049 public interface Error<T> {
050
051 /**
052 * Calculates the <em>overall</em> error of a given program tree. The error
053 * is calculated from the {@link LossFunction} and, if desired, the program
054 * {@link Complexity}.
055 *
056 * @param program the program tree which calculated the {@code calculated}
057 * values
058 * @param calculated the calculated function values
059 * @param expected the expected function values
060 * @return the overall program error
061 * @throws NullPointerException if one of the arguments is {@code null}
062 */
063 double apply(
064 final Tree<? extends Op<T>, ?> program,
065 final T[] calculated,
066 final T[] expected
067 );
068
069
070 /**
071 * Creates an error function which only uses the given {@code loss} function
072 * for calculating the program error
073 *
074 * @param <T> the sample type
075 * @param loss the loss function to use for calculating the program error
076 * @return an error function which uses the loss function for error
077 * calculation
078 * @throws NullPointerException if the given {@code loss} function is
079 * {@code null}
080 */
081 static <T> Error<T> of(final LossFunction<T> loss) {
082 requireNonNull(loss);
083 return (p, c, e) -> loss.apply(c, e);
084 }
085
086 /**
087 * Creates an error function by combining the given {@code loss} function
088 * and program {@code complexity}. The loss function and program complexity
089 * is combined in the following way: {@code error = loss + loss*complexity}.
090 * The complexity function penalizes programs which grows to big.
091 *
092 * @param <T> the sample type
093 * @param loss the loss function
094 * @param complexity the program complexity measure
095 * @return a new error function by combining the given loss and complexity
096 * function
097 * @throws NullPointerException if one of the functions is {@code null}
098 */
099 static <T> Error<T>
100 of(final LossFunction<T> loss, final Complexity<T> complexity) {
101 return of(loss, complexity, (lss, cpx) -> lss + lss*cpx);
102 }
103
104 /**
105 * Creates an error function by combining the given {@code loss} function
106 * and program {@code complexity}. The loss function and program complexity
107 * is combined in the following way: {@code error = loss + loss*complexity}.
108 * The complexity function penalizes programs which grows to big.
109 *
110 * @param <T> the sample type
111 * @param loss the loss function
112 * @param complexity the program complexity measure
113 * @param compose the function which composes the {@code loss} and
114 * {@code complexity} function
115 * @return a new error function by combining the given loss and complexity
116 * function
117 * @throws NullPointerException if one of the functions is {@code null}
118 */
119 static <T> Error<T> of(
120 final LossFunction<T> loss,
121 final Complexity<T> complexity,
122 final DoubleBinaryOperator compose
123 ) {
124 requireNonNull(loss);
125 requireNonNull(complexity);
126 requireNonNull(compose);
127
128 return (p, c, e) ->
129 compose.applyAsDouble(loss.apply(c, e), complexity.apply(p));
130 }
131
132 }
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