Efficient multivariable frequency response computations

An efficient algorithm is presented for the reliable computation of frequency response matrices of the form P(jωl-A)-1Q. Efficiency is achieved through an initial reduction of A to upper Hessenberg form H so that (jωl-H) remains upper Hessenberg as ω is varied over a desired range. Linear systems with upper Hessenberg coefficient matrices can then be solved easily and accurately.