I. Introduction
Clustering is the task of grouping a set of objects in such a way that the objects in one group are more similar to one another than the objects in other groups. Clustering can be considered as the most important unsupervised learning problem[5]. Clustering is used in exploring data mining, machine learning, pattern recognition, image analysis and data compression [9]. Clustering analysis is not itself an algorithm but it is generally a task which we have to solve.