/*
* 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 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)";
}
}