| package org.apache.lucene.search.similarities; |
| |
| /* |
| * 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. |
| */ |
| |
| import static org.apache.lucene.search.similarities.SimilarityBase.log2; |
| |
| /** |
| * Tf-idf model of randomness, based on a mixture of Poisson and inverse |
| * document frequency. |
| * @lucene.experimental |
| */ |
| public class BasicModelIne extends BasicModel { |
| |
| /** Sole constructor: parameter-free */ |
| public BasicModelIne() {} |
| |
| @Override |
| public final float score(BasicStats stats, float tfn) { |
| long N = stats.getNumberOfDocuments(); |
| long F = stats.getTotalTermFreq(); |
| double ne = N * (1 - Math.pow((N - 1) / (double)N, F)); |
| return tfn * (float)(log2((N + 1) / (ne + 0.5))); |
| } |
| |
| @Override |
| public String toString() { |
| return "I(ne)"; |
| } |
| } |
