Regular Pairings for Non-quadratic Lyapunov Functions and Contraction Analysis

TL;DR

This paper unifies various theories of pairings related to stability and contraction analysis using Lyapunov functions, introducing regular pairings and computational tools for polyhedral norms.

Contribution

It characterizes regular pairings satisfying key properties, unifies existing theories, and develops computational tools for polyhedral norms in contraction analysis.

Findings

Proves equivalence of curve norm derivative formula and Lumer's inequality.

Introduces and characterizes regular pairings satisfying key properties.

Develops computational tools for polyhedral norms in contraction theory.

Abstract

Recent studies on stability and contractivity have highlighted the importance of semi-inner products, which we refer to as pairings, associated with general norms. A pairing is a binary operation that relates the derivative of a curve's norm to the radius-vector of the curve and its tangent. This relationship, known as the curve norm derivative formula, is crucial when using the norm as a Lyapunov function. Another important property of the pairing, used in stability and contraction criteria, is the so-called Lumer inequality, which relates the pairing to the induced logarithmic norm. We prove that the curve norm derivative formula and Lumer's inequality are, in fact, equivalent to each other and to several simpler properties. We then introduce and characterize regular pairings that satisfy all of these properties. Our results unify several independent theories of pairings (semi-inner products) developed in previous work on functional analysis and control theory. Additionally, we introduce the polyhedral max pairing and develop computational tools for polyhedral norms, advancing contraction theory in non-Euclidean spaces.