Hexagonal circle patterns with constant intersection angles and discrete Painleve and Riccati equations

Discrete Riccati equation, hypergeometric functions and circle patterns of Schramm type

Square grid circle patterns with prescribed intersection angles, mimicking holomorphic maps z^a and log(z) are studied. It is shown that the corresponding circle patterns are imbedded and described by special separatrix solutions of discrete Painleve and Riccati equations. General solution of this Riccati equation is expressed in terms of the hypergeometric function. Global properties of these solutions, as well as of the discrete z^a and log(z), are established.

Finite-order meromorphic solutions and the discrete Painleve equations

Let w(z) be a finite-order meromorphic solution of the second-order difference equation w(z+1)+w(z-1) = R(z,w(z)) (eqn 1) where R(z,w(z)) is rational in w(z) and meromorphic in z. Then either w(z) satisfies a difference linear or Riccati equation or else equation (1) can be transformed to one of a list of canonical difference equations. This list consists of all known difference Painleve equation of the form (1), together with their autonomous versions. This suggests that the existence of finite-order meromorphic solutions is a good detector of integrable difference equations.

Malmquist 型 q-差分方程的零级亚纯解

Zero order meromorphic solutions of $q$-difference equations of Malmquist type

本文研究 Malmquist 型 q-差分方程 f(qz)^n=R(z,f)，证明当 |q|≠1 时其零级超越亚纯解仅存在于可约化为 q-差分线性或 Riccati 方程的方程中，并给出自治情形的显式解及差分 Painlevé 性质的应用。