On the extension of analytic solutions of a class of first-order q-difference equations

Abstract

In this paper, we use the Banach fixed point theorem to examine the existence of meromorphic solutions to the following first-order $q$-difference equation \begin{align}\tag{†}\label{dagger} y(qz)=\frac{a_1(z)y(z)+a_2(z)y(z)^2+\dots+a_p(z)y(z)^p}{1+b_1(z)y(z)+\cdots +b_t(z)y(z)^t}, \end{align} where $q\in \mathbb{C},$ $a_1(z),\dots ,a_p(z);b_1(z),\dots ,b_t(z)$ are all meromorphic functions. We establish sufficient conditions ensuring the existence and uniqueness of meromorphic solutions that can be extended to the entire complex plane $\mathbb{C}.$ More precisely, we have the following result. If $\left|q\right|\ge 3$ and \[|a_1(z)| = \max_{1 \le j \le p} |a_j(z)| \le \frac{1}{|z|}, \quad \max_{1 \le k \le t} |b_k(z)| \le \frac{1}{|z|}, \quad z \in \{\, |\Re(z)| \ge ρ> 0 \,\}, \] and $y(0)\ne \infty ,$ then we prove that~\eqref{dagger} admits a unique meromorphic solution in $D(\rho ),$ which can be extended meromorphically to $\mathbb{C}.$ Moreover, if $a_1(z)\equiv 0,$ the conclusion still holds. Furthermore, if $\left|q\right|\ge 6$ and \begin{gather*} |a_1(z)| \le \frac{1}{|q|}, \quad |a_j(z)| \le |q|^{|z|} \quad (2 \le j \le p), \quad |b_k(z)| \le |q|^{|z|} \quad (1 \le k \le t), \\[4pt] z \in D(ρ,σ) = \{\, z : |\Re(z)| \le ρ,\; |\Im(z)| \le σ, \,\, ρ>0,\,\, σ>0 \,\}, \end{gather*} and $y(0)\ne \infty ,$ then we prove that \eqref{dagger} admits a unique meromorphic solution in $D(\rho ,\sigma ),$ which can also be extended meromorphically to $\mathbb{C}.$ This conclusion remains valid in the case where $a_1(z)\equiv 0.$

15 pages