An analysis is made of the existence, uniqueness and globally asymptotical stability of the
equilibrium point of Hopfield neural networks. Without assuming the boundedness, monotonicity
and differentiability of the activation functions, the conditions ensuring existence and uniqueness of
the equilibrium are obtained. Using M-matrix theory, Liapunov function is constructed and
employed to establish sufficient conditions for global asymptotic stability. These results are
applicable to symmetric or nonsymmetric interconnection matrices, and to continuous non-monotonic
neuron activation function