/*
* 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.
*/
using System;
using FieldInvertState = Lucene.Net.Index.FieldInvertState;
namespace Lucene.Net.Search
{
/// Expert: Default scoring implementation.
[Serializable]
public class DefaultSimilarity:Similarity
{
/// Implemented as
/// state.getBoost()*lengthNorm(numTerms)
, where
/// numTerms
is {@link FieldInvertState#GetLength()} if {@link
/// #setDiscountOverlaps} is false, else it's {@link
/// FieldInvertState#GetLength()} - {@link
/// FieldInvertState#GetNumOverlap()}.
///
/// WARNING: This API is new and experimental, and may suddenly
/// change.
///
public override float ComputeNorm(System.String field, FieldInvertState state)
{
int numTerms;
if (discountOverlaps)
numTerms = state.GetLength() - state.GetNumOverlap();
else
numTerms = state.GetLength();
return (float) (state.GetBoost() * LengthNorm(field, numTerms));
}
/// Implemented as 1/sqrt(numTerms)
.
public override float LengthNorm(System.String fieldName, int numTerms)
{
return (float) (1.0 / System.Math.Sqrt(numTerms));
}
/// Implemented as 1/sqrt(sumOfSquaredWeights)
.
public override float QueryNorm(float sumOfSquaredWeights)
{
return (float) (1.0 / System.Math.Sqrt(sumOfSquaredWeights));
}
/// Implemented as sqrt(freq)
.
public override float Tf(float freq)
{
return (float) System.Math.Sqrt(freq);
}
/// Implemented as 1 / (distance + 1)
.
public override float SloppyFreq(int distance)
{
return 1.0f / (distance + 1);
}
/// Implemented as log(numDocs/(docFreq+1)) + 1
.
public override float Idf(int docFreq, int numDocs)
{
return (float) (System.Math.Log(numDocs / (double) (docFreq + 1)) + 1.0);
}
/// Implemented as overlap / maxOverlap
.
public override float Coord(int overlap, int maxOverlap)
{
return overlap / (float) maxOverlap;
}
// Default false
protected internal bool discountOverlaps;
/// Determines whether overlap tokens (Tokens with
/// 0 position increment) are ignored when computing
/// norm. By default this is false, meaning overlap
/// tokens are counted just like non-overlap tokens.
///
/// WARNING: This API is new and experimental, and may suddenly
/// change.
///
///
///
///
public virtual void SetDiscountOverlaps(bool v)
{
discountOverlaps = v;
}
///
///
public virtual bool GetDiscountOverlaps()
{
return discountOverlaps;
}
}
}