Problem: Given a number of things, x_i where i=1..n, each thing having a number of attributes, x_i1,...,x_im, which are variously discrete or continuous values, how many classes (clusters, groups, species, types, ...) do the things belong to? Note that the number of classes and the specifications of the classes have not been given; they are part of the problem too. This problem is variously known as clustering, intrinsic classification, mixture modelling, numerical taxonomy, and unsupervised classification in different disciplines.

The Model Class

Snob program,

Factor Snob program,

Mixture Modelling,

etc.