Discrete orthogonal polynomials and discrete Painlevé equations

Suppose that in some discrete set of points on a line, say on natural numbers, a certain weight function is given, and we want to construct a set of polynomials orthogonal with respect to a given weight. The standard Gram-Schmidt procedure is not effective. A faster approach is to use a recursive procedure based on the so-called three-term linear relationship. But for many weights, the coefficients of this relation in a complex way depend on the recursion step. We will consider one such example where this dependence turns out to be given by a discrete Painlevé equation, and show how the general algebraic-geometric theory of Painlevé equations helps to work effectively with problems of this type. It turns out that the class of important applied problems in which discrete Painlevé equations arise is sufficiently large. One of the objectives of the talk is to show how to recognize and bring to a standard form equations of this type (joint work with Galina Filipuk (Warsaw) and Alexander Stokes (London)). (Based on https://arxiv.org/abs/1910.10981).