  In this paper we present a direct adaptive control method for a class of
uncertain nonlinear systems with a time-varying structure. We view the
nonlinear systems as composed of a finite number of ``pieces,'' which are
interpolated by functions that depend on a possibly exogenous scheduling
variable. We assume that each piece is in strict feedback form, and show that
the method yields stability of all signals in the closed-loop, as well as
convergence of the state vector to a residual set around the equilibrium, whose
size can be set by the choice of several design parameters. The class of
systems considered here is a generalization of the class of strict feedback
systems traditionally considered in the backstepping literature. We also
provide design guidelines based on L-infinity bounds on the transient.
