Hierarchical clustering animated through pair swaps of elements from an initial state Q to a final state P (determined from the order of the leaves in the hierarchical clustering dendrogram).
For example, if Q = ('A', 'B', 'C', 'D') and P = ('C', 'A', 'D', 'B') then we have the following swaps
Q = ('A', 'B', 'C', 'D') [swap: 'A' <-> 'C']
('C', 'B', 'A', 'D') [swap: 'B' <-> 'A']
('C', 'A', 'B', 'D') [swap: 'B' <-> 'D']
('C', 'A', 'D', 'B') = P
