This book aims to provide a unified treatment of input/output modelling
and of control for discrete-time dynamical systems subject to random
disturbances. The results presented are of wide applica- bility in
control engineering, operations research, econometric modelling and many
other areas. There are two distinct approaches to mathematical modelling
of physical systems: a direct analysis of the physical mechanisms that
comprise the process, or a 'black box' approach based on analysis of
input/output data. The second approach is adopted here, although of
course the properties ofthe models we study, which within the limits of
linearity are very general, are also relevant to the behaviour of
systems represented by such models, however they are arrived at. The
type of system we are interested in is a discrete-time or sampled-data
system where the relation between input and output is (at least
approximately) linear and where additive random dis- turbances are also
present, so that the behaviour of the system must be investigated by
statistical methods. After a preliminary chapter summarizing elements of
probability and linear system theory, we introduce in Chapter 2 some
general linear stochastic models, both in input/output and state-space
form. Chapter 3 concerns filtering theory: estimation of the state of a
dynamical system from noisy observations. As well as being an important
topic in its own right, filtering theory provides the link, via the
so-called innovations representation, between input/output models (as
identified by data analysis) and state-space models, as required for
much contemporary control theory.