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 */
017package org.apache.commons.math3.ml.distance;
018
019import org.apache.commons.math3.exception.DimensionMismatchException;
020import org.apache.commons.math3.util.FastMath;
021import org.apache.commons.math3.util.MathArrays;
022
023/**
024 * Calculates the Canberra distance between two points.
025 *
026 * @since 3.2
027 */
028public class CanberraDistance implements DistanceMeasure {
029
030    /** Serializable version identifier. */
031    private static final long serialVersionUID = -6972277381587032228L;
032
033    /** {@inheritDoc} */
034    public double compute(double[] a, double[] b)
035    throws DimensionMismatchException {
036        MathArrays.checkEqualLength(a, b);
037        double sum = 0;
038        for (int i = 0; i < a.length; i++) {
039            final double num = FastMath.abs(a[i] - b[i]);
040            final double denom = FastMath.abs(a[i]) + FastMath.abs(b[i]);
041            sum += num == 0.0 && denom == 0.0 ? 0.0 : num / denom;
042        }
043        return sum;
044    }
045
046}