1. Some methods for classification and analysis of multivariate observations;MacQueen,1967
2. Clustering by means of medoids;Kaufman,1987
3. FCM: the fuzzy c-means clustering algorithm;Bezdek;Comput. Geosci.,1984
4. Fuzzy clustering with fuzzy covariance matrix;Gustafson,1979
5. Unsupervised optimal fuzzy clustering;Gath;IEEE Trans. Pattern Anal. Mach. Intell.,1989