WKB asymptotics of meromorphic solutions of difference equations

Abstract

We consider the difference Schr{\''o}dinger equation $\psi(z+h)+\psi(z-h)+ v(z)\psi(z)=0$ where $z$ is a complex variable and $h$ is a small positive parameter. If $v$ is an analytic function, then, for $h$ sufficiently small, the analytic solutions to this equation have standard semi-classical behavior that can be described by means of an analog of the complex WKB method for differential equations. In the present paper, we assume that $v$ has a simple pole and, in its neighborhood, we study the asymptotics of meromorphic solutions to the difference Schr{\''o}dinger equation.