public override sealed float Score(BasicStats stats, float tfn)
{
long N = stats.NumberOfDocuments;
long n = stats.DocFreq;
return(tfn * (float)(SimilarityBase.Log2((N + 1) / (n + 0.5))));
}
public override sealed float Score(BasicStats stats, float tfn)
{
long N = stats.NumberOfDocuments;
long F = stats.TotalTermFreq;
return(tfn * (float)(SimilarityBase.Log2(1 + (N + 1) / (F + 0.5))));
}
public override sealed float Score(BasicStats stats, float tfn)
{
// just like in BE, approximation only holds true when F << N, so we use lambda = F / (N + F)
double F = stats.TotalTermFreq + 1;
double N = stats.NumberOfDocuments;
double lambda = F / (N + F);
// -log(1 / (lambda + 1)) -> log(lambda + 1)
return((float)(SimilarityBase.Log2(lambda + 1) + tfn * SimilarityBase.Log2((1 + lambda) / lambda)));
}
public override sealed float Tfn(BasicStats stats, float tf, float len)
{
return((float)(tf * SimilarityBase.Log2(1 + c * stats.AvgFieldLength / len)));
}
