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 package org.apache.commons.math4.legacy.ml.distance; 18 19 import org.apache.commons.math4.core.jdkmath.JdkMath; 20 import org.apache.commons.math4.legacy.core.MathArrays; 21 22 /** 23 * Calculates the Earh Mover's distance (also known as Wasserstein metric) between two distributions. 24 * 25 * @see <a href="http://en.wikipedia.org/wiki/Earth_mover's_distance">Earth Mover's distance (Wikipedia)</a> 26 * 27 * @since 3.3 28 */ 29 public class EarthMoversDistance implements DistanceMeasure { 30 /** {@inheritDoc} */ 31 @Override 32 public double compute(double[] a, double[] b) { 33 MathArrays.checkEqualLength(a, b); 34 double lastDistance = 0; 35 double totalDistance = 0; 36 for (int i = 0; i < a.length; i++) { 37 final double currentDistance = (a[i] + lastDistance) - b[i]; 38 totalDistance += JdkMath.abs(currentDistance); 39 lastDistance = currentDistance; 40 } 41 return totalDistance; 42 } 43 }