Uniform exponential stability of linear time-varying systems:: revisited

Some classical results known in the adaptive control literature are often used as analysis tools for nonlinear systems by evaluating the nonlinear differential equations along trajectories. While this technique is widely used, as we remark through examples, one must take special care in the consideration of the initial conditions in order to conclude uniform convergence. One way of taking care explicitly of the initial conditions is to study parameterized linear time-varying systems. This paper re-establishes known results for linear time-varying systems via new techniques while stressing the importance of imposing that the formulated sufficient and necessary conditions must hold uniformly in the parameter. Our proofs are based on modem tools which can be interpreted as an integral version of Lyapunov theorems; rather than on the concept of uniform complete observability which is most common in the literature. (C) 2002 Elsevier Science B.V. All rights reserved.