  This paper investigates the robustness of exponential stability of a class of
switched systems described by linear functional differential equations under
arbitrary switching. We will measure the stability robustness of such a system,
subject to parameter affine perturbations of its constituent subsystems
matrices, by introducing the notion of structured stability radius. The lower
bounds and the upper bounds for this radius are established under the
assumption that certain associated positive linear systems upper bounding the
given subsystems have a common linear copositive Lyapunov function. In the case
of switched positive linear systems with discrete multiple delays or
distributed delay the obtained results yield some tractably computable bounds
for the stability radius. Examples are given to illustrate the proposed method.
