ABSTRACT
The impulse-invariant approximation, although useful for conveying the fundamental relationships between analog and digital systems, is not accurate enough in most cases where digital simulation is the primary objective. Digital models of continuous systems can be classified in various ways: One way is to classify models in terms of the signals being processed by the model. Digital modeling plays an important role in modern systems analysis. It is used to test complicated and expensive system designs on the computer, so that construction costs are limited to software until the design is completed. There are plenty of applications of this in areas like navigation, guidance, and control systems for aerospace vehicles, nuclear reactors, radar tracking, and communication systems. The chapter describes input-invariant models apply generally to either of the two classes. They are error-free for specific input functions and more or less accurate for others, depending on how much the other functions differ from the specified function.
