We will look at the hierarchical options available first. The former is non-hierarchical clustering or partitioning. The latter is hierarchical clustering. It is useful for synoptic clustering, and for all clustering work where another method cannot be explicitly justified. Thus the internal storage required is large.
Computational time is slightly higher than the latter option.
This, and the two following methods, are included for completeness and for consistency with other software packages, but are not recommended for general use. It is not guaranteed that these criterion values will vary monotonically, and this may present difficulty with the interpretation of the dendrogram representation. As in the case of the last option, reversals or inversions in the hierarchy are possible. The Minimal Spanning Tree, which is closely related to the single link method, has been used in such applications as interferogram analysis and in galaxy clustering studies. For both, a partition of minimum variance, given the number of clusters, is sought.