  In this paper, we present a hybrid direct-indirect model reference adaptive
controller (MRAC), to address a class of problems with matched and unmatched
uncertainties. In the proposed architecture, the unmatched uncertainty is
estimated online through a companion observer model. Upon convergence of the
observer, the unmatched uncertainty estimate is remodeled into a state
dependent linear form to augment the nominal system dynamics. Meanwhile, a
direct adaptive controller designed for a switching system cancels the effect
of matched uncertainty in the system and achieves reference model tracking. We
demonstrate that the proposed hybrid controller can handle a broad class of
nonlinear systems with both matched and unmatched uncertainties
