
7.4 neural network arChiteCtures 195
representation and control, fault tolerance, and content-addressable memory.
Hopfield proposed a network where all the units are bi-state units—either
“on” or “off.” These states are also represented as “active” and “inactive.” Here,
the weight of the connections between the neurons has to be set in such a
way that the network is stable. The Hopfield model consists of a single layer
of processing elements, where each unit is connected to many other units in
the network. If each unit is connected to every other unit, then the structure
is said to be fully connected. It is also a symmetrically weighted network, ...