Example $4\mathrm{.}5$ A SOM to cluster letters from different fonts: no topological structure If no structure is assumed for the cluster units. i$.$e$.,$ if only the winning unit is allowed to learn the pattern presented, the $21$ patterns form $5$ clusters:

UNIT

$313161824$

PATTERNS

C$1,$ C$2,$ C$3$

B$1,$ B$3,$ D$1,$ D$3,$ E$1,$ K$1,$ K$3$

A$1,$ A$2,$ A$3,$ J$1,$ J$2,$ J$3$

B$2,$ D$2,$ E$2,$ K$2$