1. Gabel, R.A. and Roberts, R.A., 1980. Signals and Linear Systems. Wiley, New York, 415 pp.
Among the seven chapters in this book, we note particularly Ch. 3, pp. 110–168, on State variables*, something that is frequently met with in the modem literature. This chapter presents state variable formulation and solution for discretetime systems, followed by the corresponding treatment with regard to continuoustime systems.
*State variables=important properties.