

mcxarray speed up using metric inequality:
   The choice of reference objects, from which all object distances will be
   calculated, can vary in different approaches. Examples of metric trees include
   the Vantage Point (VP) tree (Yianilos, 1992), M-tree (Ciaccia et al., 1997)
   and GNAT (Brin, 1995). All variations of such trees, exploit the distances to
   the reference points in conjunction with the triangle inequality to prune
   parts of the tree, where no closer matches (to the ones already discovered)
   can be found. A recent use of VP-trees for time-series search under Euclidean
   distance using compressed Fourier descriptors can be found in (Vlachos et al.,
   2004).

   mcxtest utilised a flat collection of vantage points.
   Incorporating a tree might add significant power?

