A positive realness test for interval plants

The purpose of this study is to consider the interval plants and propose positive realness test of extreme numerical simplicity. The stability part of the test involves the four Kharitonov polynomials, while the nonnegativity part requires checking a single (numerical) polynomial for nonnegativity. It is shown that this fact implies that Lur´e-type systems with interval plants can be tested for absolute stability by checking the positivity of a single polynomial using the modified Routh area