Discretizations of the generalized AKNS scheme

TL;DR

This paper explores space discretizations of the matrix AKNS scheme, deriving solutions via Darboux transforms, and establishing hierarchies and integral transforms for discrete matrix nonlinear equations.

Contribution

It introduces novel solutions and hierarchies for discretized matrix AKNS models, including the DNLS and AL models, using Darboux transforms and discrete Gelfand-Levitan-Marchenko equations.

Findings

Derived solutions via Darboux transforms for discrete models

Identified matrix DNLS and AL hierarchies and Lax pairs

Presented discrete Gelfand-Levitan-Marchenko equations and solutions

Abstract

We consider space discretizations of the matrix Zakharov-Shabat AKNS scheme, in particular the discrete matrix non-linear Scrhr\"odinger (DNLS) model, and the matrix generalization of the Ablowitz-Ladik (AL) model, which is the more widely acknowledged discretization. We focus on the derivation of solutions via local Darboux transforms for both discretizations, and we derive novel solutions via generic solutions of the associated discrete linear equations. The continuum analogue is also discussed, and as an example we identify solutions of the matrix NLS equation in terms of the heat kernel. In this frame we also derive a discretization of the Burgers equation via the analogue of the Cole-Hopf transform. Using the basic Darboux transforms for each scheme we identify both matrix DNLS-like and AL hierarchies, i.e. we extract the associated Lax pairs, via the dressing process. We also discuss the global Darboux transform, which is the discrete analogue of the integral transform, through the discrete Gelfand-Levitan-Marchenko (GLM) equation. The derivation of the discrete matrix GLM equation and associated solutions are also presented together with explicit linearizations. Particular emphasis is given in the discretization schemes, i.e. forward/backward in the discrete matrix DNLS scheme versus symmetric in the discrete matrix AL model.