beagled/Lucene.Net/Search/DefaultSimilarity.cs

   1 /*
   2  * Copyright 2004 The Apache Software Foundation
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  * http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 using System;
  17 namespace Lucene.Net.Search
  18 {
  19         /// <summary>Expert: Default scoring implementation. </summary>
  20         public class DefaultSimilarity:Similarity
  21         {
  22                 /// <summary>Implemented as <code>1/sqrt(numTerms)</code>. </summary>
  23                 public override float LengthNorm(System.String fieldName, int numTerms)
  24                 {
  25                         return (float) (1.0 / System.Math.Sqrt(numTerms));
  26                 }
  27
  28                 /// <summary>Implemented as <code>1/sqrt(sumOfSquaredWeights)</code>. </summary>
  29                 public override float QueryNorm(float sumOfSquaredWeights)
  30                 {
  31                         return (float) (1.0 / System.Math.Sqrt(sumOfSquaredWeights));
  32                 }
  33
  34                 /// <summary>Implemented as <code>sqrt(freq)</code>. </summary>
  35                 public override float Tf(float freq)
  36                 {
  37                         return (float) System.Math.Sqrt(freq);
  38                 }
  39
  40                 /// <summary>Implemented as <code>1 / (distance + 1)</code>. </summary>
  41                 public override float SloppyFreq(int distance)
  42                 {
  43                         return 1.0f / (distance + 1);
  44                 }
  45
  46                 /// <summary>Implemented as <code>log(numDocs/(docFreq+1)) + 1</code>. </summary>
  47                 public override float Idf(int docFreq, int numDocs)
  48                 {
  49                         return (float) (System.Math.Log(numDocs / (double) (docFreq + 1)) + 1.0);
  50                 }
  51
  52                 /// <summary>Implemented as <code>overlap / maxOverlap</code>. </summary>
  53                 public override float Coord(int overlap, int maxOverlap)
  54                 {
  55                         return overlap / (float) maxOverlap;
  56                 }
  57         }
  58 }