On the second function of cluster validity indexes

A cluster validity index for fuzzy partitions has two functions. One is to identify the number of clusters of an unlabeled data set. The other is to assess the clustering result of an unlabeled data set. The first function has been thoroughly investigated. However, no researchers attach importance to the second function. This paper devises an experiment to investigate the second function of current cluster validity indexes associating with intra-cluster compactness and inter-cluster separation. Tested by various real world data sets, current cluster validity indexes are disappointing in terms of their second function.