Lossless scalar functions: Boundary interpolation, Schur algorithm and Ober’s canonical form.

In [1] a balanced canonical form for continuous-time lossless systems was presented. This form has a tridiagonal dynamical matrix A and the useful property that the corresponding controllability matrix K is upper triangular. In [2], this structure is also derived from a LC ladder. In this paper, a connection is established between Ober¿s canonical form and a Schur algorithm built from angular derivative interpolation conditions. It provides a new interpretation of the parameters in Ober¿s form as interpolation values at infinity and a recursive construction of the balanced realization.