Fejér–Riesz factorizations and the structure of bivariate polynomials orthogonal on the bi-circle
Jeffrey S. Geronimo
Georgia Institute of Technology, Atlanta, USAPlamen Iliev
Georgia Institute of Technology, Atlanta, USA
Abstract
We give a complete characterization of the positive trigonometric polynomials on the bi-circle, which can be factored as where is a polynomial nonzero for and . The conditions are in terms of recurrence coefficients associated with the polynomials in lexicographical and reverse lexicographical ordering orthogonal with respect to the weight on the bi-circle. We use this result to describe how specific factorizations of weights on the bi-circle can be translated into identities relating the recurrence coefficients for the corresponding polynomials and vice versa. In particular, we characterize the Borel measures on the bi-circle for which the coefficients multiplying the reverse polynomials associated with the two operators: multiplication by in lexicographical ordering and multiplication by in reverse lexicographical ordering vanish after a particular point. This can be considered as a spectral type result analogous to the characterization of the Bernstein-Szeg\H{o} measures on the unit circle.
Cite this article
Jeffrey S. Geronimo, Plamen Iliev, Fejér–Riesz factorizations and the structure of bivariate polynomials orthogonal on the bi-circle. J. Eur. Math. Soc. 16 (2014), no. 9, pp. 1849–1880
DOI 10.4171/JEMS/477