Frequency-domain reduction of linear systems using Schwarz approximation

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Abstract
A frequency domain approach for reducing linear, time-invariant systems is presented which produces stable approximations of stable systems. The method is based upon the Schwarz canonical form and is shown to have a continued-fraction representation. A link between this method and the popular Routh approximation is also given. Further, the Schwarz approximation is combined with a moments-matching technique to improve steady-state responses to step and polynomial inputs. Examples are given to illustrate the methods.