001/*
002 * Copyright (c) 2015-2020, Oracle and/or its affiliates. All rights reserved.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *     http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.tribuo.classification.dtree.impurity;
018
019import com.oracle.labs.mlrg.olcut.provenance.ConfiguredObjectProvenance;
020import com.oracle.labs.mlrg.olcut.provenance.impl.ConfiguredObjectProvenanceImpl;
021
022/**
023 * A log_e entropy impurity measure.
024 */
025public class Entropy implements LabelImpurity {
026
027    @Override
028    public double impurityNormed(double[] input) {
029        double score = 0.0;
030
031        for (int i = 0; i < input.length; i++) {
032            double d = input[i];
033            if (Math.abs(d) > 1e-10) {
034                score -= d * Math.log(d);
035            }
036        }
037
038        return score;
039    }
040
041    @Override
042    public String toString() {
043        return "Entropy";
044    }
045
046    @Override
047    public ConfiguredObjectProvenance getProvenance() {
048        return new ConfiguredObjectProvenanceImpl(this,"LabelImpurity");
049    }
050}