Single-linkage algorithm

Hierarchical algorithms are characterized by the construction of a tree-like structure. A single linkage algorithm starts with placing in the first cluster the two nearest points. At the next stage, a third point joins the already formed cluster of two if its shortest distance to the members of the first cluster is smaller than to any other point. 

There is a wide variety of hierarchical algorithms available and it is impossible to discuss all of them here. Therefore, we shall only explain the most typical ones, namely the single linkage, the complete linkage and the average linkage methods. 

Allen, F. H., Doyle, M. J., and Taylor, R. / Automated conformational analysis from crystallographic data. 1. A symmetry-modified single-linkage clustering algorithm for three-dimensional pattern recognition. Acta Cryst. B47, 29-40 (1991). 

Different algorithms may produce radically different results when applied to the same dataset. For example, the single-linkage method has difficulty in recognizing two separate clusters linked by a chain of intervening observations (a situation par-... 

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