Robust absolute stability for interval Yakubovich type control system (Q1191683)

Consider the system \(\dot x=Ax-b\varphi(\sigma)\), \(\dot\sigma=c^* x- \rho\varphi(\sigma)\) with \(\sigma\varphi(\sigma)>0\), well-known as the zero-root critical case of the absolute stability. All the coefficients are supposed to satisfy interval inequalities. Absolute stability for all possible coefficients is called robust absolute stability. Various sufficient conditions for robust absolute stability are given, expressed in the language of the coefficients. No proofs are given and only two references which are earlier author's papers. (Possibly the one published in Int. J. Control 45, 203-210 (1987; Zbl 0611.15016) could contain more information).