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 <code>z</code>.
* @param z represents <code>A/(A+1)</code> where <code>A</code>
* 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 <code>z</code>
* @see #NormalizationZ(float)
*/
public float getZ() {
return z;
}
}