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arXiv · 2601.04783

Szeg\H{o} Mapping and Hermite--Pad\'{e} Polynomials for Multiple Orthogonality on the Unit Circle

Rostyslav Kozhan·Marcus Vaktnäs
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Abstract

We investigate generalized Laurent multiple orthogonal polynomials on the unit circle satisfying simultaneous orthogonality conditions with respect to $r$ probability measures or linear functionals on the unit circle. We show that these polynomials can be characterized as solutions of a general two-point Hermite--Pad\'e approximation problem. We derive Szeg\H{o}-type recurrence relations, establish compatibility conditions for the associated recurrence coefficients, and obtain Christoffel--Darboux formulas as well as Heine-type determinantal representations. Furthermore, by extending the Szeg\H{o} mapping and the Geronimus relations, we relate these Laurent multiple orthogonal polynomials to multiple orthogonal polynomials on the real line, thereby making explicit the connection between multiple orthogonality on the unit circle and on the real line.

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Rostyslav Kozhan, Marcus Vaktnäs. 2026-01-08. Szeg\H{o} Mapping and Hermite--Pad\'{e} Polynomials for Multiple Orthogonality on the Unit Circle. https://arxiv.org/abs/2601.04783

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