Computes a score factor based on a term's document frequency (the number of documents which contain the term). This value is multiplied by the {@link #Tf(int)} factor for each term in the query and these products are then summed to form the initial score for a document.

Terms that occur in fewer documents are better indicators of topic, so implementations of this method usually return larger values for rare terms, and smaller values for common terms.

public abstract float Idf(
	int docFreq,
	int numDocs
)

Public MustOverride Function Idf ( _
	docFreq As Integer, _
	numDocs As Integer _
) As Single

public:
virtual float Idf(
	int docFreq, 
	int numDocs
) abstract