The inverse document frequency is a measure of how much information a term provides, that is, whether the term is common or rare across all documents.
# Inverse document frequency
#
# The inverse document frequency is a measure of how much information a term
# provides, that is, whether the term is common or rare across all documents.
var inverse_doc_frequency = new Vector
lib/vsm/vsm.nit:144,2--148,39