As Qjgs symmetric positive-definite matrix, then [z.sup.T](t)[Q.sub.1]z(t) > 0, and is an indefinite matrix, from of the inequality in Equation (31) if [z.sup.T](t)Mz(t) > 0 then f(t) = -[z.sup.T](t)[Q.sub.1]z(t)/[z.sup.T]Mz(t) but it is assumed that f(t) [greater than or equal to] 0.