Continued-fraction expansion about two or more points: a flexible approach to linear system reduction

Model reduction by continued-fraction expansion about two or more points, including the general point s = a, is shown to be a real alternative to the methods which guarantee stability. Suitable choice of a is seen to overcome the problem of unstable reduced models while still retaining the maximum number of full system parameters in the model.

Simple extension of the method to more than one general point is outlined, providing a link with pole retention methods and the consequences are discussed.

A new criterion for choosing a is suggested and its use is demonstrated in some examples, which compare the method directly with stability based methods.