ABSOLUTE AND INPUT-TO-STATE STABILITIES OF NONAUTONOMOUS SYSTEMS WITH CAUSAL MAPPINGS

We consider systems governed by the scalar equation Xn k=0 ak(t)x (n−k) (t) = [Fx](t) (t ≥ 0), where a0 ≡ 1; ak(t) (k = 1, . . ., n) are positive continuous functions and F is a causal mapping. We also consider the case when F depends on the input. Such equations include differential, integrodifferential and other traditional equations. It is assumed that all the roots rk(t) (k = 1, . . ., n) of the polynomial z n + a1(t)z n−1 + · · · + an(t) are real and negative for all t ≥ 0. Exact explicit conditions for the absolute and input-to-state stabilities of the considered systems are established.