| /* |
| * 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; |
| |
| /** |
| * Computes lambda as {@code totalTermFreq+1 / numberOfDocuments+1}. |
| * @lucene.experimental |
| */ |
| public class LambdaTTF extends Lambda { |
| |
| /** Sole constructor: parameter-free */ |
| public LambdaTTF() {} |
| |
| @Override |
| public final float lambda(BasicStats stats) { |
| float lambda = (float) ((stats.getTotalTermFreq() + 1.0) / (stats.getNumberOfDocuments() + 1.0)); |
| if (lambda == 1) { |
| // Distribution SPL cannot work with values of lambda that are equal to 1 |
| lambda = Math.nextUp(lambda); |
| } |
| return lambda; |
| } |
| |
| public final Explanation explain(BasicStats stats) { |
| return Explanation.match( |
| lambda(stats), |
| getClass().getSimpleName() |
| + ", computed as (F + 1) / (N + 1) from:", |
| Explanation.match(stats.getTotalTermFreq(), |
| "F, total number of occurrences of term across all documents"), |
| Explanation.match(stats.getNumberOfDocuments(), |
| "N, total number of documents with field")); |
| } |
| |
| @Override |
| public String toString() { |
| return "L"; |
| } |
| } |