Regular Pairings for Non-quadratic Lyapunov Functions and Contraction Analysis
For researchers in stability and contraction analysis, this work provides a unified theoretical foundation for pairings associated with general norms, enabling broader application of Lyapunov and contraction methods.
The paper unifies several independent theories of pairings (semi-inner products) by proving the equivalence of the curve norm derivative formula and Lumer's inequality, and introduces regular pairings that satisfy all these properties. It also introduces the polyhedral max pairing with computational tools for polyhedral norms, advancing contraction theory in non-Euclidean spaces.
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.