Increasing delay as a strategy to prove stability

TL;DR

This paper introduces an expansion strategy that increases delay in difference equations to establish local and global stability, offering an alternative to traditional methods like Jury's algorithm.

Contribution

The paper presents a novel expansion strategy for difference equations that simplifies stability analysis and extends to global stability using embedding techniques.

Findings

Fixed point stability characterized by gradient norms

Strategy provides an alternative to Jury's algorithm

Effective in diverse discrete-time systems

Abstract

We consider difference equations of the form $x_{n+1}=F_0(x_n,\ldots,x_{n-k+1}),$ and increase the delay through a process of successive substitutions to obtain a sequence of systems $y_{n+1}=F_j(x_{n-j},\ldots,x_{n-k-j+1}),\; j=0,1,\ldots$. We call this process \emph{the expansion strategy} and use it to establish novel results that enable us to prove stability. When the map $F_0$ is sufficiently smooth and has a hyperbolic fixed point, we show the fixed point is locally asymptotically stable if and only if $\|\nabla F_j\|_1<1$ for some finite number $j$. Our local stability results complement recent results obtained on Schur stability, and they can provide an alternative to the highly acclaimed Jury's algorithm. Also, we show the effectiveness of the expansion strategy in obtaining global stability results. Global stability results are obtained by integrating the expansion strategy with the embedding technique. Finally, we give illustrative examples to show the results' practical applicability across various discrete-time dynamical systems.