content: /*
   * Tencent is pleased to support the open source community by making Angel available.
   *
   * Copyright (C) 2017-2018 THL A29 Limited, a Tencent company. All rights reserved.
   *
   * Licensed 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
   *
   * https://opensource.org/licenses/Apache-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 com.tencent.angel.sona.tree.objective.loss;
  
  import com.tencent.angel.sona.tree.objective.metric.EvalMetric;
  import com.tencent.angel.sona.tree.util.MathUtil;
  
  import javax.inject.Singleton;
  
  @Singleton
  public class BinaryLogisticLoss implements BinaryLoss {
      private static BinaryLogisticLoss instance;
  
      private BinaryLogisticLoss() {}
  
      @Override
      public Kind getKind() {
          return Kind.BinaryLogistic;
      }
  
      @Override
      public EvalMetric.Kind defaultEvalMetric() {
          return EvalMetric.Kind.LOG_LOSS;
      }
  
      @Override
      public double firOrderGrad(float pred, float label) {
          double prob = MathUtil.fastSigmoid(pred);
          return prob - label;
      }
  
      @Override
      public double secOrderGrad(float pred, float label) {
          double prob = MathUtil.fastSigmoid(pred);
          return Math.max(prob * (1 - prob), MathUtil.EPSILON);
      }
  
      @Override
      public double secOrderGrad(float pred, float label, double firGrad) {
          double prob = firGrad + label;
          return Math.max(prob * (1 - prob), MathUtil.EPSILON);
      }
  
      public static BinaryLogisticLoss getInstance() {
          if (instance == null)
              instance = new BinaryLogisticLoss();
          return instance;
      }
  }
  