Minimal realizations of linear systems: The "shortest basis" approach
Provides a conceptually simpler method for constructing minimal realizations of linear systems, relevant to control theory researchers.
The paper introduces a 'shortest basis' approach for minimal realizations of linear systems, showing that the dimensions of minimal state and transition spaces equal the number of active generators in such a basis, leading to simpler controller and observer canonical forms.
Given a controllable discrete-time linear system C, a shortest basis for C is a set of linearly independent generators for C with the least possible lengths. A basis B is a shortest basis if and only if it has the predictable span property (i.e., has the predictable delay and degree properties, and is non-catastrophic), or alternatively if and only if it has the subsystem basis property (for any interval J, the generators in B whose span is in J is a basis for the subsystem C_J). The dimensions of the minimal state spaces and minimal transition spaces of C are simply the numbers of generators in a shortest basis B that are active at any given state or symbol time, respectively. A minimal linear realization for C in controller canonical form follows directly from a shortest basis for C, and a minimal linear realization for C in observer canonical form follows directly from a shortest basis for the orthogonal system C^\perp. This approach seems conceptually simpler than that of classical minimal realization theory.