Zeros of quasi-paraorthogonal polynomials and positive quadrature

Abstract

In this paper we illustrate that paraorthogonality on the unit circle T is the counterpart to orthogonality on R when we are interested in the spectral properties. We characterize quasi-paraorthogonal polynomials on the unit circle as the analogues of the quasi-orthogonal polynomials on R. We analyse the possibilities of preselecting some of its zeros, in order to build positive quadrature formulas with prefixed nodes and maximal domain of validity. These quadrature formulas on the unit circle are illustrated numerically.