Since the outstanding and pioneering research work of Hopfield on
recurrent neural networks (RNNs) in the early 80s of the last century,
neural networks have rekindled strong interests in scientists and
researchers. Recent years have recorded a remarkable advance in research
and development work on RNNs, both in theoretical research as weIl as
actual applications. The field of RNNs is now transforming into a
complete and independent subject. From theory to application, from
software to hardware, new and exciting results are emerging day after
day, reflecting the keen interest RNNs have instilled in everyone, from
researchers to practitioners. RNNs contain feedback connections among
the neurons, a phenomenon which has led rather naturally to RNNs being
regarded as dynamical systems. RNNs can be described by continuous time
differential systems, discrete time systems, or functional differential
systems, and more generally, in terms of non- linear systems. Thus, RNNs
have to their disposal, a huge set of mathematical tools relating to
dynamical system theory which has tumed out to be very useful in
enabling a rigorous analysis of RNNs.