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 * 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
18 package org.apache.commons.math4.neuralnet;
19
20 import org.apache.commons.math4.neuralnet.internal.NeuralNetException;
21
22 /**
23 * Euclidean distance measures of n-dimensional vectors.
24 *
25 * @since 4.0
26 */
27 public class EuclideanDistance implements DistanceMeasure {
28 /** {@inheritDoc} */
29 @Override
30 public double applyAsDouble(double[] a,
31 double[] b) {
32 final int len = a.length;
33 if (len != b.length) {
34 throw new NeuralNetException(NeuralNetException.SIZE_MISMATCH,
35 len, b.length);
36 }
37
38 double sum = 0;
39 for (int i = 0; i < len; i++) {
40 final double diff = a[i] - b[i];
41 sum += diff * diff;
42 }
43 return Math.sqrt(sum);
44 }
45 }