The fuzzy set was conceived as a result of an attempt to come to grips
with the problem of pattern recognition in the context of imprecisely
defined categories. In such cases, the belonging of an object to a class
is a matter of degree, as is the question of whether or not a group of
objects form a cluster. A pioneering application of the theory of fuzzy
sets to cluster analysis was made in 1969 by Ruspini. It was not until
1973, however, when the appearance of the work by Dunn and Bezdek on the
Fuzzy ISODATA (or fuzzy c-means) algorithms became a landmark in the
theory of cluster analysis, that the relevance of the theory of fuzzy
sets to cluster analysis and pattern recognition became clearly
established. Since then, the theory of fuzzy clustering has developed
rapidly and fruitfully, with the author of the present monograph
contributing a major share of what we know today. In their seminal work,
Bezdek and Dunn have introduced the basic idea of determining the fuzzy
clusters by minimizing an appropriately defined functional, and have
derived iterative algorithms for computing the membership functions for
the clusters in question. The important issue of convergence of such
algorithms has become much better understood as a result of recent work
which is described in the monograph.