  We propose a new discrete-time adaptive algorithm for parameter estimation of
a class of time-varying plants. The main contribution is the inclusion of a
time-varying gain matrix in the adjustment of the parameter estimates. We show
that in the presence of time-varying unknown parameters, the parameter
estimation error converges uniformly to a compact set under conditions of
persistent excitation, with the size of the compact set proportional to the
time-variation of the unknown parameters. Under conditions of finite
excitation, the convergence is asymptotic and non-uniform.
