Discrete-time systems arise as a matter of course in modelling
biological or economic processes. For systems and control theory they
are of major importance, particularly in connection with digital control
applications. If sampling is performed in order to control periodic
processes, almost periodic systems are obtained. This is a strong
motivation to investigate the discrete-time systems with time-varying
coefficients. This research monograph contains a study of discrete-time
nodes, the discrete counterpart of the theory elaborated by Bart,
Gohberg and Kaashoek for the continuous case, discrete-time Lyapunov and
Riccati equations, discrete-time Hamiltonian systems in connection with
input-output operators and associated Hankel and Toeplitz operators. All
these tools aim to solve the problems of stabilization and attenuation
of disturbances in the framework of H2- and H-control theory. The book
is the first of its kind to be devoted to these topics and consists
mainly of original, recently obtained results.