Canonical lossless state-space systems: Staircase forms and the Schur algorithm

TL;DR

This paper introduces a finite set of balanced canonical forms for multivariate discrete-time lossless systems, extending previous continuous-time results and connecting to the tangential Schur algorithm for system interpolation.

Contribution

It generalizes balanced canonical forms to multivariate systems, linking them with the tangential Schur algorithm and providing a minimal finite atlas for lossless and input-normal systems.

Findings

Finite atlas of overlapping balanced canonical forms for multivariate systems

Connection established between canonical forms and the tangential Schur algorithm

Results enable minimal canonical form representations for stable systems

Abstract

A new finite atlas of overlapping balanced canonical forms for multivariate discrete-time lossless systems is presented. The canonical forms have the property that the controllability matrix is positive upper triangular up to a suitable permutation of its columns. This is a generalization of a similar balanced canonical form for continuous-time lossless systems. It is shown that this atlas is in fact a finite sub-atlas of the infinite atlas of overlapping balanced canonical forms for lossless systems that is associated with the tangential Schur algorithm; such canonical forms satisfy certain interpolation conditions on a corresponding sequence of lossless transfer matrices. The connection between these balanced canonical forms for lossless systems and the tangential Schur algorithm for lossless systems is a generalization of the same connection in the SISO case that was noted before. The results are directly applicable to obtain a finite sub-atlas of multivariate input-normal canonical forms for stable linear systems of given fixed order, which is minimal in the sense that no chart can be left out of the atlas without losing the property that the atlas covers the manifold.