-package org.apache.lucene.search;
-
-import org.apache.lucene.index.FieldInvertState;
-
-/**
- * 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.
- */
-
-/** Expert: Default scoring implementation. */
-public class DefaultSimilarity extends Similarity {
-
- /** Implemented as
- * <code>state.getBoost()*lengthNorm(numTerms)</code>, where
- * <code>numTerms</code> is {@link FieldInvertState#getLength()} if {@link
- * #setDiscountOverlaps} is false, else it's {@link
- * FieldInvertState#getLength()} - {@link
- * FieldInvertState#getNumOverlap()}.
- *
- * @lucene.experimental */
- @Override
- public float computeNorm(String field, FieldInvertState state) {
- final int numTerms;
- if (discountOverlaps)
- numTerms = state.getLength() - state.getNumOverlap();
- else
- numTerms = state.getLength();
- return state.getBoost() * ((float) (1.0 / Math.sqrt(numTerms)));
- }
-
- /** Implemented as <code>1/sqrt(sumOfSquaredWeights)</code>. */
- @Override
- public float queryNorm(float sumOfSquaredWeights) {
- return (float)(1.0 / Math.sqrt(sumOfSquaredWeights));
- }
-
- /** Implemented as <code>sqrt(freq)</code>. */
- @Override
- public float tf(float freq) {
- return (float)Math.sqrt(freq);
- }
-
- /** Implemented as <code>1 / (distance + 1)</code>. */
- @Override
- public float sloppyFreq(int distance) {
- return 1.0f / (distance + 1);
- }
-
- /** Implemented as <code>log(numDocs/(docFreq+1)) + 1</code>. */
- @Override
- public float idf(int docFreq, int numDocs) {
- return (float)(Math.log(numDocs/(double)(docFreq+1)) + 1.0);
- }
-
- /** Implemented as <code>overlap / maxOverlap</code>. */
- @Override
- public float coord(int overlap, int maxOverlap) {
- return overlap / (float)maxOverlap;
- }
-
- // Default true
- protected boolean discountOverlaps = true;
-
- /** Determines whether overlap tokens (Tokens with
- * 0 position increment) are ignored when computing
- * norm. By default this is true, meaning overlap
- * tokens do not count when computing norms.
- *
- * @lucene.experimental
- *
- * @see #computeNorm
- */
- public void setDiscountOverlaps(boolean v) {
- discountOverlaps = v;
- }
-
- /** @see #setDiscountOverlaps */
- public boolean getDiscountOverlaps() {
- return discountOverlaps;
- }
-}