and is known as nonrecursive, because the previous values of the output do not appear
Differential and difference equations have broad application in the description of physical laws and are useful for relating rates of change of variables and other parameters of a system or its components. In actuality, LTI systems do not exist. All physical systems are nonlinear to some extent. Fortunately, a large percentage of systems can be represented by LTI models over a limited operating range. Many systems always operate within this linear range. Other systems exceed the limits of linear operation, but may be approximated by LTI systems.