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
  17 using System;
  18
  19 namespace Lucene.Net.Search
  20 {
  21
  22         /// <summary>Expert: Default scoring implementation. </summary>
  23         [Serializable]
  24         public class DefaultSimilarity : Similarity
  25         {
  26                 /// <summary>Implemented as <code>1/sqrt(numTerms)</code>. </summary>
  27                 public override float LengthNorm(System.String fieldName, int numTerms)
  28                 {
  29                         return (float) (1.0 / System.Math.Sqrt(numTerms));
  30                 }
  31
  32                 /// <summary>Implemented as <code>1/sqrt(sumOfSquaredWeights)</code>. </summary>
  33                 public override float QueryNorm(float sumOfSquaredWeights)
  34                 {
  35                         return (float) (1.0 / System.Math.Sqrt(sumOfSquaredWeights));
  36                 }
  37
  38                 /// <summary>Implemented as <code>sqrt(freq)</code>. </summary>
  39                 public override float Tf(float freq)
  40                 {
  41                         return (float) System.Math.Sqrt(freq);
  42                 }
  43
  44                 /// <summary>Implemented as <code>1 / (distance + 1)</code>. </summary>
  45                 public override float SloppyFreq(int distance)
  46                 {
  47                         return 1.0f / (distance + 1);
  48                 }
  49
  50                 /// <summary>Implemented as <code>log(numDocs/(docFreq+1)) + 1</code>. </summary>
  51                 public override float Ldf(int docFreq, int numDocs)
  52                 {
  53                         return (float) (System.Math.Log(numDocs / (double) (docFreq + 1)) + 1.0);
  54                 }
  55
  56                 /// <summary>Implemented as <code>overlap / maxOverlap</code>. </summary>
  57                 public override float Coord(int overlap, int maxOverlap)
  58                 {
  59                         return overlap / (float) maxOverlap;
  60                 }
  61         }
  62 }