01 /*
02 * Java Genetic Algorithm Library (jenetics-5.1.0).
03 * Copyright (c) 2007-2019 Franz Wilhelmstötter
04 *
05 * Licensed under the Apache License, Version 2.0 (the "License");
06 * you may not use this file except in compliance with the License.
07 * You may obtain a copy of the License at
08 *
09 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 * Author:
18 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
19 */
20 package io.jenetics.ext.moea;
21
22 import java.util.function.Function;
23 import java.util.function.ToDoubleBiFunction;
24
25 /**
26 * Defines the distance of two elements of a given <em>vector</em> type {@code V}.
27 * The following example creates an {@code ElementDistance} function for a
28 * {@code double[] array}:
29 * <pre>{@code
30 * final ElementDistance<double[]> dist = (u, v, i) -> u[i] - v[i];
31 * }</pre>
32 *
33 * @param <V> the vector type
34 *
35 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
36 * @version 4.1
37 * @since 4.1
38 */
39 @FunctionalInterface
40 public interface ElementDistance<V> {
41
42 /**
43 * Calculates the distance of two vector elements at the given {@code index}.
44 * E.g.
45 * <pre>{@code
46 * final ElementDistance<double[]> dist = (u, v, i) -> u[i] - v[i];
47 * }</pre>
48 *
49 * @param u the first vector
50 * @param v the second vector
51 * @param index the vector index
52 * @return the distance of the two element vectors
53 */
54 public double distance(final V u, final V v, final int index);
55
56 /**
57 * Return an element distance function for the mapped type {@code T}.
58 *
59 * @param mapper the mapper function
60 * @param <T> the new distance type
61 * @return an element distance function for the mapped type {@code T}
62 */
63 public default <T> ElementDistance<T>
64 map(final Function<? super T, ? extends V> mapper) {
65 return (u, v, i) -> distance(mapper.apply(u), mapper.apply(v), i);
66 }
67
68 /**
69 * Return a function which calculates the distance of two vector elements at
70 * a given {@code index}.
71 *
72 * @param index the vector index
73 * @return a function which calculates the distance of two vector elements
74 */
75 public default ToDoubleBiFunction<V, V> ofIndex(final int index) {
76 return (u, v) -> distance(u, v, index);
77 }
78
79 }
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