DefaultSimilarity.cs
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上传日期:2013-09-30
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文件大小:2k
- /*
- * Copyright 2004 The Apache Software Foundation
- *
- * Licensed 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.
- */
- using System;
- namespace Lucene.Net.Search
- {
-
- /// <summary>Expert: Default scoring implementation. </summary>
- [Serializable]
- public class DefaultSimilarity : Similarity
- {
- /// <summary>Implemented as <code>1/sqrt(numTerms)</code>. </summary>
- public override float LengthNorm(System.String fieldName, int numTerms)
- {
- return (float) (1.0 / System.Math.Sqrt(numTerms));
- }
-
- /// <summary>Implemented as <code>1/sqrt(sumOfSquaredWeights)</code>. </summary>
- public override float QueryNorm(float sumOfSquaredWeights)
- {
- return (float) (1.0 / System.Math.Sqrt(sumOfSquaredWeights));
- }
-
- /// <summary>Implemented as <code>sqrt(freq)</code>. </summary>
- public override float Tf(float freq)
- {
- return (float) System.Math.Sqrt(freq);
- }
-
- /// <summary>Implemented as <code>1 / (distance + 1)</code>. </summary>
- public override float SloppyFreq(int distance)
- {
- return 1.0f / (distance + 1);
- }
-
- /// <summary>Implemented as <code>log(numDocs/(docFreq+1)) + 1</code>. </summary>
- public override float Ldf(int docFreq, int numDocs)
- {
- return (float) (System.Math.Log(numDocs / (double) (docFreq + 1)) + 1.0);
- }
-
- /// <summary>Implemented as <code>overlap / maxOverlap</code>. </summary>
- public override float Coord(int overlap, int maxOverlap)
- {
- return overlap / (float) maxOverlap;
- }
- }
- }