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 * Licensed to the Apache Software Foundation (ASF) under one or more
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 * 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
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 * 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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package org.apache.lucene.search.similarities;

import org.apache.lucene.search.Explanation;

F3EXP is defined as Sum(tf(term_doc_freq)*IDF(term)-gamma(docLen, queryLen)) where IDF(t) = ln((N+1)/df(t)) N=total num of docs, df=doc freq gamma(docLen, queryLen) = (docLen-queryLen)*queryLen*s/avdl NOTE: the gamma function of this similarity creates negative scores
@lucene.experimental
/** * F3EXP is defined as Sum(tf(term_doc_freq)*IDF(term)-gamma(docLen, queryLen)) * where IDF(t) = ln((N+1)/df(t)) N=total num of docs, df=doc freq * gamma(docLen, queryLen) = (docLen-queryLen)*queryLen*s/avdl * NOTE: the gamma function of this similarity creates negative scores * @lucene.experimental */
public class AxiomaticF3LOG extends Axiomatic {
Constructor setting s and queryLen, letting k to default
Params:
  • s – hyperparam for the growth function
  • queryLen – the query length
/** * Constructor setting s and queryLen, letting k to default * * @param s hyperparam for the growth function * @param queryLen the query length */
public AxiomaticF3LOG(float s, int queryLen) { super(s, queryLen); } @Override public String toString() { return "F3LOG"; }
compute the term frequency component
/** * compute the term frequency component */
@Override protected double tf(BasicStats stats, double freq, double docLen) { freq += 1; // otherwise gives negative scores for freqs < 1 return 1 + Math.log(1 + Math.log(freq)); }
compute the document length component
/** * compute the document length component */
@Override protected double ln(BasicStats stats, double freq, double docLen) { return 1.0; }
compute the mixed term frequency and document length component
/** * compute the mixed term frequency and document length component */
@Override protected double tfln(BasicStats stats, double freq, double docLen) { return 1.0; }
compute the inverted document frequency component
/** * compute the inverted document frequency component */
@Override protected double idf(BasicStats stats, double freq, double docLen) { return Math.log((stats.getNumberOfDocuments() + 1.0) / stats.getDocFreq()); }
compute the gamma component
/** * compute the gamma component */
@Override protected double gamma(BasicStats stats, double freq, double docLen) { return (docLen - this.queryLen) * this.s * this.queryLen / stats.getAvgFieldLength(); } @Override protected Explanation tfExplain(BasicStats stats, double freq, double docLen){ return Explanation.match((float) tf(stats, freq, docLen), "tf, term frequency computed as 1 + log(1 + log(freq)) from:", Explanation.match((float) freq, "freq, number of occurrences of term in the document")); }; @Override protected Explanation lnExplain(BasicStats stats, double freq, double docLen){ return Explanation.match((float) ln(stats, freq, docLen), "ln, document length, equals to 1"); }; protected Explanation tflnExplain(BasicStats stats, double freq, double docLen){ return Explanation.match((float) tfln(stats, freq, docLen), "tfln, mixed term frequency and document length, equals to 1"); }; protected Explanation idfExplain(BasicStats stats, double freq, double docLen){ return Explanation.match((float) idf(stats, freq, docLen), "idf, inverted document frequency computed as log((N + 1) / n) from:", Explanation.match((float) stats.getNumberOfDocuments(), "N, total number of documents with field"), Explanation.match((float) stats.getDocFreq(), "n, number of documents containing term")); }; }