org.apache.lucene.search.similarities.DistributionLL Maven / Gradle / Ivy
/*
* 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,
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* See the License for the specific language governing permissions and
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package org.apache.lucene.search.similarities;
/**
* Log-logistic distribution.
* Unlike for DFR, the natural logarithm is used, as
* it is faster to compute and the original paper does not express any
* preference to a specific base.
* @lucene.experimental
*/
public class DistributionLL extends Distribution {
/** Sole constructor: parameter-free */
public DistributionLL() {}
@Override
public final double score(BasicStats stats, double tfn, double lambda) {
return -Math.log(lambda / (tfn + lambda));
}
@Override
public String toString() {
return "LL";
}
}