Almost all orbits of an analogue of the Collatz map on the reals attain bounded values

Abstract

Motivated by a balanced ternary representation of the Collatz map we define the map $C_\mathbb{R}$ on the positive real numbers by setting $C_\mathbb{R}(x)=\frac{1}{2}x$ if $[x]$ is even and $C_\mathbb{R}(x)=\frac{3}{2}x$ if $[x]$ is odd, where $[x]$ is defined by $[x]\in\mathbb{Z}$ and $x-[x]\in(-\frac{1}{2},\frac{1}{2}]$. We show that there exists a constant $K>0$ such that the set of $x$ fulfilling $\liminf_{n\in\mathbb{N}}C_\mathbb{R}^n(x)\leq K$ is Lebesgue-co-null. We also show that for any $\epsilon>0$ the set of $x$ for which $ (\frac{3^{\frac{1}{2}}}{2})^kx^{1-\epsilon}\leq C_\mathbb{R}^k(x)\leq (\frac{3^{\frac{1}{2}}}{2})^kx^{1+\epsilon}$ for all $0\leq k\leq \frac{1}{1-\frac{\log_23}{2}}\log_2x$ is large for a suitable notion of largeness.