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.
