AIMSVSW 2018: Orthogonal Polynomials pp 293-333

# Two Variable Orthogonal Polynomials and Fejér-Riesz Factorization

Conference paper
Part of the Tutorials, Schools, and Workshops in the Mathematical Sciences book series (TSWMS)

## Abstract

We consider bivariate polynomials orthogonal on the bicircle with respect to a positive nondegenerate measure. The theory of scalar and matrix orthogonal polynomials is reviewed with an eye toward applying it to the bivariate case. The lexicographical and reverse lexicographical orderings are used to order the monomials for the Gram–Schmidt procedues and recurrence formulas are derived between the polynomials of different degrees. These formulas link the orthogonal polynomials constructed using the lexicographical ordering with those constructed using the reverse lexicographical ordering. Relations between the coefficients in the recurrence formulas are derived and used to give necessary and sufficient conditions for the existence of a positive measure. These results are then used to construct a class of two variable measures supported on the bicircle that are given by one over the magnitude squared of a stable polynomial. Applications to Fejér–Riesz factorization are also given.

## Keywords

Orthogonal polynomials on the bicircle Fejér-Riesz factorization Recurrence relations Matrix orthogonal polynomials on the unit circle Bivariate orthogonal polynomials Matrix orthogonal polynomials moment problem Recurrence coefficients

42C05 42C10

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