The Orbit Problem for Parametric Linear Dynamical Systems

TL;DR

This paper investigates the parametric Orbit Problem for linear dynamical systems, establishing decidability for one parameter and linking the multi-parameter case to the Skolem Problem, indicating increased complexity.

Contribution

It proves decidability for the orbit problem with a single parameter and connects the multi-parameter case to the Skolem Problem, highlighting potential intractability.

Findings

Decidability established for one-parameter systems.

Reduction from the Skolem Problem for multi-parameter systems.

Indication of intractability for systems with two or more parameters.

Abstract

We study a parametric version of the Kannan-Lipton Orbit Problem for linear dynamical systems. We show decidability in the case of one parameter and Skolem-hardness with two or more parameters. More precisely, consider a $d$-dimensional square matrix $M$ whose entries are algebraic functions in one or more real variables. Given initial and target vectors $u,v\in \mathbb{Q}^d$, the parametric point-to-point orbit problem asks whether there exist values of the parameters giving rise to a concrete matrix $N \in \mathbb{R}^{d\times d}$, and a positive integer $n\in \mathbb{N}$, such that $N^nu = v$. We show decidability for the case in which $M$ depends only upon a single parameter, and we exhibit a reduction from the well-known Skolem Problem for linear recurrence sequences, suggesting intractability in the case of two or more parameters.