| /* |
| * 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; |
| |
| import static org.apache.lucene.search.similarities.SimilarityBase.log2; |
| |
| /** |
| * An approximation of the <em>I(n<sub>e</sub>)</em> model. |
| * @lucene.experimental |
| */ |
| public class BasicModelIF extends BasicModel { |
| |
| /** Sole constructor: parameter-free */ |
| public BasicModelIF() {} |
| |
| @Override |
| public final double score(BasicStats stats, double tfn, double aeTimes1pTfn) { |
| long N = stats.getNumberOfDocuments(); |
| long F = stats.getTotalTermFreq(); |
| double A = log2(1 + (N + 1) / (F + 0.5)); |
| |
| // basic model IF should return A * tfn |
| // which we rewrite to A * (1 + tfn) - A |
| // so that it can be combined with the after effect while still guaranteeing |
| // that the result is non-decreasing with tfn |
| |
| return A * aeTimes1pTfn * (1 - 1 / (1 + tfn)); |
| } |
| |
| @Override |
| public Explanation explain(BasicStats stats, double tfn, double aeTimes1pTfn) { |
| return Explanation.match( |
| (float) (score(stats, tfn, aeTimes1pTfn) * (1 + tfn) / aeTimes1pTfn), |
| getClass().getSimpleName() + ", computed as " + |
| "tfn * log2(1 + (N + 1) / (F + 0.5)) from:", |
| Explanation.match((float) tfn, "tfn, normalized term frequency"), |
| Explanation.match(stats.getNumberOfDocuments(), |
| "N, total number of documents with field"), |
| Explanation.match(stats.getTotalTermFreq(), |
| "F, total number of occurrences of term across all documents")); |
| } |
| |
| @Override |
| public String toString() { |
| return "I(F)"; |
| } |
| } |