Model reduction of dynamic systems over a frequency interval

Model reduction of linear, time-invariant, single-input., single-output systems over desired frequency intervals (low-pass, band-pass and high-pass) is considered in this paper. Order reduction is effected by manipulating two orthogonal polynomial series, one representing the high-order system and the other representing the approximating low-order model. The method is a generalization of the classical Padd approximations, however, by a special transformation it becomes the simple (classical) Pade problem, thus retaining the computational attractiveness of the latter.