The problem of controlling or stabilizing a system of differential equa-
tions in the presence of random disturbances is intuitively appealing
and has been a motivating force behind a wide variety of results grouped
loosely together under the heading of "Stochastic Control." This book is
concerned with a special instance of this general problem, the "Adaptive
LQ Regulator," which is a stochastic control problem of partially
observed type that can, in certain cases, be solved explicitly. We first
describe this problem, as it is the focal point for the entire book, and
then describe the contents of the book. The problem revolves around an
uncertain linear system x(O) = x in R", where 0 E {1, ..., N} is a
random variable representing this uncertainty and (Ai' B, C) and xJ are
the coefficient matrices and initial state, respectively, of j j a
linear control system, for eachj = 1, ..., N. A common assumption is
that the mechanism causing this uncertainty is additive noise, and that
conse- quently the "controller" has access only to the observation
process y( . ) where y = Cex + .