This book is a revision of Stochastic Processes in Information and
Dynamical Systems written by the first author (E.W.) and published in
1971. The book was originally written, and revised, to provide a
graduate level text in stochastic processes for students whose primary
interest is its applications. It treats both the traditional topic of
sta- tionary processes in linear time-invariant systems as well as the
more modern theory of stochastic systems in which dynamic structure
plays a profound role. Our aim is to provide a high-level, yet readily
acces- sible, treatment of those topics in the theory of
continuous-parameter stochastic processes that are important in the
analysis of information and dynamical systems. The theory of stochastic
processes can easily become abstract. In dealing with it from an applied
point of view, we have found it difficult to decide on the appropriate
level of rigor. We intend to provide just enough mathematical machinery
so that important results can be stated PREFACE vi with precision and
clarity; so much ofthe theory of stochastic processes is inherently
simple if the suitable framework is provided. The price of providing
this framework seems worth paying even though the ul- timate goal is in
applications and not the mathematics per se.