Approximating the Frequency Response of Contractive Systems

TL;DR

This paper presents a method to approximate the periodic solutions of contractive systems with explicit error bounds, demonstrating their low-pass filter behavior and applying the approach to biological systems.

Contribution

It introduces an approximation technique for periodic solutions of contractive systems using simpler systems, with explicit error bounds based on input-to-state stability.

Findings

Approximate periodic solutions with explicit error bounds.

Contractive systems with periodic inputs behave like low pass filters.

Application to systems biology examples.

Abstract

We consider contractive systems whose trajectories evolve on a compact and convex state-space. It is well-known that if the time-varying vector field of the system is periodic then the system admits a unique globally asymptotically stable periodic solution. Obtaining explicit information on this periodic solution and its dependence on various parameters is important both theoretically and in numerous applications. We develop an approach for approximating such a periodic trajectory using the periodic trajectory of a simpler system (e.g. an LTI system). Our approximation includes an error bound that is based on the input-to-state stability property of contractive systems. We show that in some cases this error bound can be computed explicitly. We also use the bound to derive a new theoretical result, namely, that a contractive system with an additive periodic input behaves like a low pass filter. We demonstrate our results using several examples from systems biology.