| /* |
| * 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. |
| */ |
| package org.apache.lucene.search.similarities; |
| |
| |
| import org.apache.lucene.search.Explanation; |
| |
| /** |
| * Dirichlet Priors normalization |
| * @lucene.experimental |
| */ |
| public class NormalizationH3 extends Normalization { |
| private final float mu; |
| |
| /** |
| * Calls {@link #NormalizationH3(float) NormalizationH3(800)} |
| */ |
| public NormalizationH3() { |
| this(800F); |
| } |
| |
| /** |
| * Creates NormalizationH3 with the supplied parameter <code>μ</code>. |
| * @param mu smoothing parameter <code>μ</code> |
| */ |
| public NormalizationH3(float mu) { |
| if (Float.isFinite(mu) == false || mu < 0) { |
| throw new IllegalArgumentException("illegal mu value: " + mu + ", must be a non-negative finite value"); |
| } |
| this.mu = mu; |
| } |
| |
| @Override |
| public double tfn(BasicStats stats, double tf, double len) { |
| return (tf + mu * ((stats.getTotalTermFreq()+1F) / (stats.getNumberOfFieldTokens()+1F))) / (len + mu) * mu; |
| } |
| |
| @Override |
| public Explanation explain(BasicStats stats, double tf, double len) { |
| return Explanation.match( |
| (float) tfn(stats, tf, len), |
| getClass().getSimpleName() |
| + ", computed as (tf + mu * ((F+1) / (T+1))) / (fl + mu) * mu from:", |
| Explanation.match((float) tf, |
| "tf, number of occurrences of term in the document"), |
| Explanation.match(mu, |
| "mu, smoothing parameter"), |
| Explanation.match((float) stats.getTotalTermFreq(), |
| "F, total number of occurrences of term across all documents"), |
| Explanation.match((float) stats.getNumberOfFieldTokens(), |
| "T, total number of tokens of the field across all documents"), |
| Explanation.match((float) len, "fl, field length of the document")); |
| } |
| |
| @Override |
| public String toString() { |
| return "3(" + mu + ")"; |
| } |
| |
| /** |
| * Returns the parameter <code>μ</code> |
| * @see #NormalizationH3(float) |
| */ |
| public float getMu() { |
| return mu; |
| } |
| } |