Hyers-Ulam stability of loxodromic M\"obius difference equation

TL;DR

This paper investigates the Hyers-Ulam stability of sequences generated by loxodromic Möbius difference equations, showing stability depends on initial conditions relative to specific avoided regions.

Contribution

It establishes conditions for Hyers-Ulam stability of loxodromic Möbius difference equations, linking stability to initial points outside certain disks.

Findings

Hyers-Ulam stability holds outside the avoided region.

The avoided region is a union of disks related to the inverse iterates of infinity.

Stability depends on the initial point's position relative to these disks.

Abstract

Hyers-Ulam of the sequence $ \{z_n\}_{n \in \mathbb{N}} $ satisfying the difference equation $ z_{i+1} = g(z_i) $ where $ g(z) = \frac{az + b}{cz + d} $ with complex numbers $ a $, $ b $, $ c $ and $ d $ is defined. Let $ g $ be loxodromic M\"obius map, that is, $ g $ satisfies that $ ad-bc =1 $ and $a + d \in \mathbb{C} \setminus [-2,2] $. Hyers-Ulam stability holds if the initial point of $ \{z_n\}_{n \in \mathbb{N}} $ is in the exterior of avoided region, which is the union of the certain disks of $ g^{-n}(\infty) $ for all $ n \in \mathbb{N} $.