| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.math4.legacy.ml.distance; |
| |
| import org.apache.commons.math4.legacy.exception.DimensionMismatchException; |
| import org.apache.commons.math4.core.jdkmath.JdkMath; |
| import org.apache.commons.math4.legacy.core.MathArrays; |
| |
| /** |
| * Calculates the Earh Mover's distance (also known as Wasserstein metric) between two distributions. |
| * |
| * @see <a href="http://en.wikipedia.org/wiki/Earth_mover's_distance">Earth Mover's distance (Wikipedia)</a> |
| * |
| * @since 3.3 |
| */ |
| public class EarthMoversDistance implements DistanceMeasure { |
| /** {@inheritDoc} */ |
| @Override |
| public double compute(double[] a, double[] b) |
| throws DimensionMismatchException { |
| MathArrays.checkEqualLength(a, b); |
| double lastDistance = 0; |
| double totalDistance = 0; |
| for (int i = 0; i < a.length; i++) { |
| final double currentDistance = (a[i] + lastDistance) - b[i]; |
| totalDistance += JdkMath.abs(currentDistance); |
| lastDistance = currentDistance; |
| } |
| return totalDistance; |
| } |
| } |