Short introduction to Vector Space Model (VSM) In information retrieval or text mining, the term frequency - inverse document frequency also called tf-idf, is
L. Diosan, M. Oltean, A. Rogozan, and J. Pecuchet. GECCO '07: Proceedings of the 9th annual conference on
Genetic and evolutionary computation, 2, page 1873--1873. London, ACM Press, (7-11 July 2007)