Volterra map and related recurrences

TL;DR

This paper analyzes the Volterra map, relates it to discrete equations and continued fractions, and introduces a unified approach using special polynomials to generalize and simplify existing results.

Contribution

It presents a compact, unified formulation of the higher-order equations associated with the Volterra map using special discrete polynomials, extending previous work.

Findings

Unified expression for all g ≥ 1 cases

Connection between discrete polynomials and continued fractions

Simplification of higher-order equations

Abstract

In this paper we analyze recent work \cite{Hone1} by Hone, Roberts and Vanhaecke, where the so-called Volterra map was introduced via the Lax equation that looks similar to the Lax representation for the Mumford's system \cite{Vanhaecke}. This map turns out to be birational and a corresponding dynamical system on an affine space $M_g$ of dimension $3g+1$ was associated with it. This mapping is related to some discrete equation of the order $2g+1$ associated with the Stieltjes continued fraction expansion of a certain function on a hyperelliptic (elliptic) curve of genus $g\geq 1$. The authors of the paper provides examples of this equation for the simplest cases $g=1$ and $g=2$, but for higher values of $g$, corresponding equation turns out to be too cumbersome to write them out. We present an approach in which the mentioned $(2g+1)$-order equation can be written out for all values of $g\geq 1$ in a compact form. This equation is not new and can be found, for example, in \cite{Svinin3}. An essential point in our framework is the use of special class of discrete polynomials which as shown to be closely related to the Stieltjes continued fraction. On the one hand, this allows us to generalize some of the results of the work \cite{Hone1}. On the other hand, many things in this approach can be presented in a more compact and unified form. Ultimately, we believe that this allows us to give a new perspective on this topic.