If the history flag HISTW
(see HIST-flags) is set during training, the WEIGHT structure points
to the first
WEIGHT_VALUE structure of a linked list. This first structure contains the
last value and points through the Hist field to its predecessor. In this
way, walking down the linked list from the WEIGHT gives a reverse
chronological list of its values. The last entry has a Hist=NULL.
The same goes for the Theta field in the UNIT structure, holding the
UNIT 's bias.
