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There is a newer version: 2024.11.18751.20241128T090041Z-241100

/*
 * COPIED FROM APACHE LUCENE 4.7.2
 *
 * Git URL: [email protected]:apache/lucene.git, tag: releases/lucene-solr/4.7.2, path: lucene/core/src/java
 *
 * (see https://issues.apache.org/jira/browse/OAK-10786 for details)
 */

package org.apache.lucene.search.similarities;

/*
 * 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.
 */

/**
 * Pareto-Zipf Normalization
 * @lucene.experimental
 */
public class NormalizationZ extends Normalization {
  final float z;

  /**
   * Calls {@link #NormalizationZ(float) NormalizationZ(0.3)}
   */
  public NormalizationZ() {
    this(0.30F);
  }

  /**
   * Creates NormalizationZ with the supplied parameter z.
   * @param z represents A/(A+1) where A 
   *          measures the specificity of the language.
   */
  public NormalizationZ(float z) {
    this.z = z;
  }
  
  @Override
  public float tfn(BasicStats stats, float tf, float len) {
    return (float)(tf * Math.pow(stats.avgFieldLength / len, z));
  }

  @Override
  public String toString() {
    return "Z(" + z + ")";
  }
  
  /**
   * Returns the parameter z
   * @see #NormalizationZ(float)
   */
  public float getZ() {
    return z;
  }
}