001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  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
018package org.apache.commons.math4.neuralnet;
019
020import org.apache.commons.math4.neuralnet.internal.NeuralNetException;
021
022/**
023 * Euclidean distance measures of n-dimensional vectors.
024 *
025 * @since 4.0
026 */
027public class EuclideanDistance implements DistanceMeasure {
028    /** {@inheritDoc} */
029    @Override
030    public double applyAsDouble(double[] a,
031                                double[] b) {
032        final int len = a.length;
033        if (len != b.length) {
034            throw new NeuralNetException(NeuralNetException.SIZE_MISMATCH,
035                                         len, b.length);
036        }
037
038        double sum = 0;
039        for (int i = 0; i < len; i++) {
040            final double diff = a[i] - b[i];
041            sum += diff * diff;
042        }
043        return Math.sqrt(sum);
044    }
045}