Building Special Linear System Realizations of Special Transfer Functions

Linear sjstem realization problems require the construction of a linear system realiization, or a quadruple of real matrices F,G, H, J, of a given real rational W ( s ) , so ithat W(s) = J + H'(sI F)-'G. When W(s) has certain properties, corresponding ;to symmetry, passivity, or losslwness, it is possible to select a realization that closely (but not necessarily exactly) reflects theseproperties. We review such possibilities, then consider a new one, initially for discrete time systems: if the impulse response mociated with W is nonnegative, can the entries of the redizing matrices be chosento be nonnegative also? Necessary and barely differing sufficient conditions are presented for this to he the case.