vi PREFACE 
ing equally well to pulsed linear filters and to the description of linear 
numerical processes. Sampled-data theory which is developed in this 
book serves as a common base for the analysis and synthesis of linear 
digital systems, pulsed continuous systems, and their combinations often 
found in practice. 
Contributions to the theory of sampled-data systems have been made 
by scientists, mathematicians, and engineers throughout the world. 
An examination of the list of references and bibliography in this book 
will reveal papers from many countries, including England, France, the 
U.S.S.R., and the United States. As in the case of all new fields, the 
research papers listed are not equally significant. The philosophy we 
have used in writing this book is that a major responsibility of the author 
is to sift, evaluate, and interpret the significant contributions. This 
is particularly important when a book is among the first, if not the first, 
in its field, for all too often its coverage tends to set the pattern for sub- 
sequent books. It would have been far easier for us to write a book 
which is merely an organized compendium of the papers in the field. 
It has been much more difficult to be selective, and we fully expect that 
others who are well-versed in this field may not agree with our choice of 
material. 
As a result of the application of this philosophy, this is a rather short 
book. We have tried to avoid overwhelming our readers with verbiage 
or confusing them with a large number of disconnected items which 
might have been included for the sake of completeness. We have 
directed this book to readers who are mature technically and who are 
capable of referring to the literature when necessary. To make this 
easier, the book is documented as fully as possible. 
This is not a book for beginners in the field of control systems. It is 
assumed that the reader is a graduate student, practicing engineer, or 
scientist who has had a thorough training in differential equations, the 
Laplace transformation and its applications, linear feedback control 
theory, and the elements of probability and statistics. On the other 
hand, it is an introductory text, and the reader need have had no prior 
contact with the theory of sampled-data systems or numerical processes. 
While specifically directed to control systems, there is much material 
in this book which has general application. This includes the z trans- 
formation, data-reconstruction theory, applications of transform methods 
to numerical processes, and the theory of sampled random time functions. 
The level of presentation is such that the book can be used as a text 
for a graduate course on the subject. Depending on the preparation of 
the students, this could be a one-semester course of three hours per week 
or a two-semester course of two hours per week. In exceptional cases, 
where the students have had a thorough grounding in linear systems, 
