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 * (the "License"); you may not use this file except in compliance with
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package org.apache.lucene.search.similarities;

import org.apache.lucene.search.Explanation;

F2EXP is defined as Sum(tfln(term_doc_freq, docLen)*IDF(term)) where IDF(t) = pow((N+1)/df(t), k) N=total num of docs, df=doc freq
@lucene.experimental
/** * F2EXP is defined as Sum(tfln(term_doc_freq, docLen)*IDF(term)) * where IDF(t) = pow((N+1)/df(t), k) N=total num of docs, df=doc freq * * @lucene.experimental */
public class AxiomaticF2EXP extends Axiomatic {
Constructor setting s and k, letting queryLen to default
Params:
  • s – hyperparam for the growth function
  • k – hyperparam for the primitive weighting function
/** * Constructor setting s and k, letting queryLen to default * @param s hyperparam for the growth function * @param k hyperparam for the primitive weighting function */
public AxiomaticF2EXP(float s, float k) { super(s, 1, k); }
Constructor setting s only, letting k and queryLen to default
Params:
  • s – hyperparam for the growth function
/** * Constructor setting s only, letting k and queryLen to default * @param s hyperparam for the growth function */
public AxiomaticF2EXP(float s) { this(s, 0.35f); }
Default constructor
/** * Default constructor */
public AxiomaticF2EXP() { super(); } @Override public String toString() { return "F2EXP"; }
compute the term frequency component
/** * compute the term frequency component */
@Override protected double tf(BasicStats stats, double freq, double docLen) { return 1.0; }
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 freq / (freq + this.s + this.s * docLen / stats.getAvgFieldLength()); }
compute the inverted document frequency component
/** * compute the inverted document frequency component */
@Override protected double idf(BasicStats stats, double freq, double docLen) { return Math.pow((stats.getNumberOfDocuments() + 1.0) / stats.getDocFreq(), this.k); }
compute the gamma component
/** * compute the gamma component */
@Override protected double gamma(BasicStats stats, double freq, double docLen) { return 0.0; } @Override protected Explanation tfExplain(BasicStats stats, double freq, double docLen){ return Explanation.match((float) tf(stats, freq, docLen), "tf, term frequency, equals to 1"); }; @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, " + "computed as freq / (freq + s + s * dl / avgdl) from:", Explanation.match((float) freq, "freq, number of occurrences of term in the document"), Explanation.match((float) docLen, "dl, length of field"), Explanation.match((float) stats.getAvgFieldLength(), "avgdl, average length of field across all documents")); }; protected Explanation idfExplain(BasicStats stats, double freq, double docLen){ return Explanation.match((float) idf(stats, freq, docLen), "idf, inverted document frequency computed as " + "Math.pow((N + 1) / n, k) from:", Explanation.match((float) stats.getNumberOfDocuments(), "N, total number of documents with field"), Explanation.match((float) stats.getDocFreq(), "n, number of documents containing term")); }; }