Friedman J., Hastie T. and Tibshirani R. (2017). The elements of statistical
learning. New York: Springer.
Thomas P. Minka (2003). Estimating a Dirichlet distribution.
http://research.microsoft.com/en-us/um/people/minka/papers/dirichlet/minka-dirichlet.pdf
Ng Kai Wang, Guo-Liang Tian and Man-Lai Tang (2011). Dirichlet and related
distributions: Theory, methods and applications. John Wiley & Sons.
Aitchison J. (1986). The statistical analysis of compositional data.
Chapman & Hall.