1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://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
18 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22 package org.hipparchus.clustering.distance;
23
24 import org.hipparchus.exception.MathIllegalArgumentException;
25 import org.hipparchus.util.FastMath;
26 import org.hipparchus.util.MathArrays;
27
28 /**
29 * Calculates the Canberra distance between two points.
30 *
31 */
32 public class CanberraDistance implements DistanceMeasure {
33
34 /** Serializable version identifier. */
35 private static final long serialVersionUID = -6972277381587032228L;
36
37 /** Empty constructor.
38 * <p>
39 * This constructor is not strictly necessary, but it prevents spurious
40 * javadoc warnings with JDK 18 and later.
41 * </p>
42 * @since 3.0
43 */
44 public CanberraDistance() { // NOPMD - unnecessary constructor added intentionally to make javadoc happy
45 // nothing to do
46 }
47
48 /** {@inheritDoc} */
49 @Override
50 public double compute(double[] a, double[] b)
51 throws MathIllegalArgumentException {
52 MathArrays.checkEqualLength(a, b);
53 double sum = 0;
54 for (int i = 0; i < a.length; i++) {
55 final double num = FastMath.abs(a[i] - b[i]);
56 final double denom = FastMath.abs(a[i]) + FastMath.abs(b[i]);
57 sum += num == 0.0 && denom == 0.0 ? 0.0 : num / denom;
58 }
59 return sum;
60 }
61
62 }