The activation of unit: the euclidian distance between the weights
and the inputs.
FUNCTION
The function traverses the linked list of incoming links - the InLinks -
and sums the squared differences of each LINK 's weight value and
the output value of the
unit it points to. Finally, this sum is divided by the UNIT 's bias (theta).
In formula:
((W1 - O1)^2 + (W2 - O2)^2 + ... + (Wn - On)^2) / B.
