unsupervised
- Tutorial: Ghahramani, Zoubin. "Unsupervised learning." Advanced Lectures on Machine Learning. Springer Berlin Heidelberg, 2004. 72-112.
- Clustering Theory : Ackerman's website
- BOOK : Hastie, Trevor, Robert Tibshirani, and Jerome Friedman. Unsupervised learning. Springer New York, 2009. (only a part of the book is available through the link).