On robust stability of discrete-time systems with real coefficients in a diamond

The robust stability problem for continuous-time systems with coefficients varying in a diamond can be considered as a `dual´ to Kharitonov´s interval polynomial problem. This paper aims at extending the above results to discrete-time systems. It has been proved that the stability of a family of polynomials with coefficients varying in a real diamond requires only to check four extremal polynomials. It can be viewed as a kind of the counterpart of Kharitonov´s result (strong version) to discrete-time systems