Chapter 2 . Unsupervised Artificial Neural Networks
27
unified-matrix (U-matrix) approach (Ultsch and Siemon 1990) will be preferred
for its ability to provide a very flexible tool for ecologists.
(a)
(b)
(c)
(d)
02
04
c.s
01
Figure 2.8. AU-matrix representation of the self-organizing map computed
using the Whittaker's relative transformation. (a) Location of the virtual units VU k
on the self-organizing map. (b) New hexagons are inserted between adjacent
hexagons. (c) Gray levels showing the distance between two adjacent hexagons.
Light for short distances and dark for large distances. (d) Each hexagon with
virtual units is colored according to the minimum of its adjacent hexagons. (e)
Sampie units mapped on the U-matrix. Plains (light areas) can be seen separated
by ravines (dark areas)
The V-Matrix Display
This method will be presented using the results obtained with the Whittaker's
relative transformation. With the V-matrix method, in order to detect a clustering