Counterexample and correction to a result on robust Schur stability of a complex-coefficient polynomials set with coefficients in a diamond

In Ref. (1), Schur stability of a family of polynomials with transformed coefficients varying in a diamond has been studied. A necessary and sufficient condition was given for the stability of the entire family if a selected set of eight edge polynomials was stable. In this paper, we show via a counterexample that this result is not correct. It turns out that 16 (for n is even) or 32 (for n is odd) edges should be selected.