I. Introduction
The bidirectional associative memory (BAM) neural networks, first proposed and researched by Kosko [1], [2] for their useful application in pattern recognition, solving optimization problems, and automatic control engineering, are a class of two-layer heteroassociative networks with and without axonal signal transmission delays. The stability of the equilibrium points ensures the stored memory can be retrieved. Therefore, the investigation on the stability of a BAM network has been the highlight in this field. The stability of this type of network has been extensively studied. In [3]–[12], by using the method of the Lyapunov functional, a lot of sufficient conditions have been given ensuring the stability of the BAM neural networks with delays. The stability criteria of delayed BAM neural networks with impulses or reaction-diffusion terms or distributed delays are derived, and we refer to [8], [11]–[17], and the references cited therein for more details.