Piecewise contractions and b-adic expansions

Symbolic dynamics of piecewise contractions

A map $f{:}\,[0,1)\to [0,1)$ is a {\it piecewise contraction of $n$ intervals} ($n$-PC) if there exist $0<λ<1$ and a partition of $[0,1)$ into intervals $I_1,\ldots,I_n$ such that $f\vert_{I_i}$ is $λ$-Lipschitz for every $1\le i\le n$. An infinite word $θ=θ_0θ_1\ldots$ over the alphabet $\mathcal{A}=\{1,\ldots,n\}$ is a {\it natural coding of} $f$ if there exists $x\in I$ such that $θ_k=i$ if and only if $f^k(x)\in I_i$. We prove that if $θ$ is a natural coding of an injective $n$-PC, then some infinite subword of $θ$ is either periodic or isomorphic to a natural coding of a topologically tra…

A $p$-adic Approach To Piecewise Polynomial Dynamical Systems

Using $p$-adic numbers, we partially categorize the cycles of a sizable class of polynomial dynamical systems. In turn, we prove a few results related to the non-trivial cycles of the $\textit{Collatz map}$ $\text{Col} : \mathbb{Z}_+ \to \mathbb{Z}_+$ defined by $$\text{Col}(n) = \begin{cases} 3n + 1, & n \text{ is odd;} \\ n/2, & \text{otherwise.}\end{cases}$$ Proving the non-existence of non-trivial Collatz cycles would reduce the Collatz conjecture to whether the Collatz map can diverge to infinity.

Dynamics of piecewise increasing contractions

Let $I_1=[a_0,a_1),\ldots,I_{k}= [a_{k-1},a_k)$ be a partition of the interval $I=[0,1)$ into $k$ subintervals. Let $f:I\to I$ be a map such that each restriction $f|_{I_i}$ is an increasing Lipschitz contraction. We prove that any $f$ admits at most $k$ periodic orbits, where the upper bound is sharp. We are also interested in the dynamics of piecewise linear $λ$-affine maps, where $0<λ<1$. Let $b_1,\ldots,b_k$ be real numbers and let $F_λ: I\to \mathbb{R}$ be a function such that each restriction $F_λ|_{I_i}(x)=λx +b_i$. Under a generic assumption on the parameters $a_1,\ldots,a_{k-1},b_1,\l…

Growth of heights in piecewise-affine planar maps

We consider the growth of heights of the points of the orbits of (piecewise) affine maps of the plane, with rational parameters. We analyse the asymptotic growth rate of both global and local ($p$-adic) heights, for the primes $p$ that divide the parameters. We show that almost all the points in a domain of linearity (such as an elliptic island in an area-preserving map) have the same exponential growth rate. We also show that the convergence of the $p$-adic height may be non-uniform, with arbitrarily large fluctuations occurring arbitrarily close to any point. We explore numerically the behav…

3-区间分段 $\lambda$-仿射压缩的旋转数与动力学

Rotation number and dynamics of 3-interval piecewise $λ$-affine contractions

本文研究3-区间分段$\lambda$-仿射压缩映射族，给定$\lambda$和$d$，确定参数$\delta$和$a$使映射具有指定旋转数，并保证其符号动力学包含相应旋转的符号动力学，从而刻画周期轨道数量与Cantor集吸引子的复杂度。

A chaotic discrete-time continuous-state Hopfield network with piecewise-affine activation functions

We construct a chaotic discrete-time continuous-state Hopfield network with piecewise-affine nonnegative activation functions and weight matrix with small positive entries. More precisely, there exists a Cantor set $C$ in the state space such that the network has sensitive dependence on initial conditions at initial states in $C$ and the network orbit of each initial state in $C$ has $C$ as its $ω$-limit set. The approach we use is based on tools developed and employed recently in the study of the topological dynamics of piecewise-contractions. The parameters of the chaotic network are explici…

Contraction analysis of switched systems: the case of Caratheodory Systems and Networks

In this paper we extend to a generic class of piecewise smooth dynamical systems a fundamental tool for the analysis of convergence of smooth dynamical systems: contraction theory. We focus on switched systems satisfying Caratheodory conditions for the existence and unicity of a solution. After generalizing the classical definition of contraction to this class of dynamical systems, we give sufficient conditions for global exponential convergence of their trajectories. The theoretical results are then applied to solve a set of representative problems including proving global asymptotic stabilit…

Outer Billiards with Contraction: Attracting Cantor Sets

We consider the outer billiards map with contraction outside polygons. We construct a 1-parameter family of systems such that each system has an open set in which the dynamics is reduced to that of a piecewise contraction on the interval. Using the theory of rotation numbers, we deduce that every point inside the open set is asymptotic to either a single periodic orbit (rational case) or a Cantor set (irrational case). In particular, we deduce existence of an attracting Cantor set for certain parameter values. Moreover, for a different choice of a 1-parameter family, we prove that the system i…

Piecewise linear iterated function systems on the line of overlapping construction

In this paper we consider Iterated Function Systems (IFS) on the real line consisting of continuous piecewise linear functions. We assume some bounds on the contraction ratios of the functions, but we do not assume any separation condition. Moreover, we do not require that the functions of the IFS are injective, but we assume that their derivatives are separated from zero. We prove that if we fix all the slopes but perturb all other parameters, then for all parameters outside of an exceptional set of less than full packing dimension, the Hausdorff dimension of the attractor is equal to the exp…

三角形上的分段压缩映射

A piecewise contractive map on triangles

研究 $\mathbb{R}^2$ 中三条直线上分段压缩映射的动力学，证明任意初始点轨道必收敛于不动点或周期轨道，且存在无穷多种依赖于空间参数的周期轨道。

Shadowing and Stability in p-adic dynamics

In this paper, we study dynamical properties as shadowing and structural stability for a class of dynamics on $\mathbb{Z}_p$ and $\mathbb{Q}_p$, where $p \geq 2$ is a prime number. In particular, we prove that if $f: \mathbb{Z}_p \to \mathbb{Z}_p$ is a $(p^{-k},p^{m})$ ( $0 < m \leq k$ integers ) locally scaling map then $f$ is shadowing and structurally stable. We also study the number of conjugacy classes of these maps and we consider the above properties for $1$-Lipschitz maps of $\mathbb{Z}_p$ and for extensions of the shift map, contractions and dilatations on $\mathbb{Q}_p$.

On the Asymptotic Properties of Piecewise Contracting Maps

We study the asymptotic dynamics of maps which are piecewise contracting on a compact space. These maps are Lipschitz continuous, with Lipschitz constant smaller than one, when restricted to any piece of a finite and dense union of disjoint open pieces. We focus on the topological and the dynamical properties of the (global) attractor of the orbits that remain in this union. As a starting point, we show that the attractor consists of a finite set of periodic points when it does not intersect the boundary of a contraction piece, which complements similar results proved for more specific classes…

Integrate and Fire Neural Networks, Piecewise Contractive Maps and Limit Cycles

We study the global dynamics of integrate and fire neural networks composed of an arbitrary number of identical neurons interacting by inhibition and excitation. We prove that if the interactions are strong enough, then the support of the stable asymptotic dynamics consists of limit cycles. We also find sufficient conditions for the synchronization of networks containing excitatory neurons. The proofs are based on the analysis of the equivalent dynamics of a piecewise continuous Poincaré map associated to the system. We show that for strong interactions the Poincaré map is piecewise contractiv…

Gluing and grazing bifurcations in periodically forced 2-dimensional integrate-and-fire models

In this work we consider a general class of $2$-dimensional hybrid systems. Assuming that the system possesses an attracting equilibrium point, we show that, when periodically driven with a square-wave pulse, the system possesses a periodic orbit which may undergo smooth and nonsmooth grazing bifurcations. We perform a semi-rigorous study of the existence of periodic orbits for a particular model consisting of a leaky integrate-and-fire model with a dynamic threshold. We use the stroboscopic map, which in this context is a $2$-dimensional piecewise-smooth discontinuous map. For some parameter …