Distance metrics

References:
[1] http://en.wikipedia.org/wiki/Cosine_similarity
[2] http://www.miislita.com/information-retrieval-tutorial/cosine-similarity-tutorial.html
[3] http://www.cedar.buffalo.edu/~srihari/CSE555/Chap4.Metrics-TangentDistance.pdf
[4] Face verifiation http://www.springerlink.com/content/95143j6058483pnw/fulltext.pdf
[5] Other distance(Weighted Euclidean distance) http://www.econ.upf.edu/~michael/stanford/maeb4.pdf
     http://stats.stackexchange.com/questions/15289/when-to-use-weighted-euclidean-distance-and-how-to-determine-the-weights-to-use
[6] Manhattan http://en.wikipedia.org/wiki/Taxicab_geometry