http://homepages.inf.ed.ac.uk/rbf/IAPR/researchers/MLPAGES/mlcode.htm
http://www.ima.umn.edu/~iwen/REU/REU_cluster.html
http://services.cbu.uib.no/software//spectrumclustering
http://www.cs.umd.edu/~mount/Projects/KMeans/
http://en.wikipedia.org/wiki/Kd-tree