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/*
 * 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.spark.ml.psf;

import com.tencent.angel.ml.matrix.psf.update.enhance.zip2.func.Zip2MapWithIndexFunc;
import io.netty.buffer.ByteBuf;

public class FTRLWUpdater implements Zip2MapWithIndexFunc {

  private double alpha;
  private double beta;
  private double lambda1;
  private double lambda2;
  private long skipIndex;

  public FTRLWUpdater() {
    super();
  }

  public FTRLWUpdater(double alpha, double beta, double lambda1, double lambda2, long skipIndex) {
    this.alpha = alpha;
    this.beta = beta;
    this.lambda1 = lambda1;
    this.lambda2 = lambda2;
    this.skipIndex = skipIndex;
  }

  @Override public double call(long index, double zVal, double nVal) {
    if (index == skipIndex) {
      return -1.0 * alpha * zVal / (beta + Math.sqrt(nVal));
    } else if (Math.abs(zVal) > lambda1) {
      return (-1) * (1.0 / (lambda2 + (beta + Math.sqrt(nVal)) / alpha)) * (zVal
        - Math.signum(zVal) * lambda1);
    } else {
      return 0.0;
    }
  }

  @Override public void serialize(ByteBuf buf) {
    buf.writeDouble(alpha);
    buf.writeDouble(beta);
    buf.writeDouble(lambda1);
    buf.writeDouble(lambda2);
    buf.writeLong(skipIndex);
  }

  @Override public void deserialize(ByteBuf buf) {
    alpha = buf.readDouble();
    beta = buf.readDouble();
    lambda1 = buf.readDouble();
    lambda2 = buf.readDouble();
    skipIndex = buf.readLong();
  }

  @Override public int bufferLen() {
    return 5 * 8;
  }

}