Moment Representations of Exceptional $X_1$ Orthogonal Polynomials

TL;DR

This paper develops determinant-based representations of $X_1$ exceptional orthogonal polynomials using adjusted moments derived from Darboux transformations, with detailed focus on Jacobi and Laguerre cases.

Contribution

It introduces a universal approach to represent $X_1$ exceptional polynomials via determinants of matrices with adjusted moments, including recursion formulas and initial moments for key systems.

Findings

Determinant representations for $X_1$ exceptional polynomials are established.

Recursion formulas for adjusted moments are derived.

Complete proofs are provided for Jacobi and Type III Laguerre cases.

Abstract

We obtain representations of $X_1$ exceptional orthogonal polynomials through determinants of matrices that have certain adjusted moments as entries. We start out directly from the Darboux transformation, allowing for a universal perspective, rather than dependent upon the particular system (Jacobi or Type of Laguerre polynomials). We include a recursion formula for the adjusted moments and provide the initial adjusted moments for each system. Throughout we relate to the various examples of $X_1$ exceptional orthogonal polynomials. We especially focus on and provide complete proofs for the Jacobi and the Type III Laguerre case, as they are less prevalent in literature. Lastly, we include a preliminary discussion explaining that the higher co-dimension setting becomes more involved. The number of possibilities and choices is exemplified, but only starts, with the lack of a canonical flag.