Abstract
In general, the zeros of an orthogonal rational function (ORF) on a subset of the real line, with poles among \({\{\alpha_1,\ldots,\alpha_n\}\subset(\mathbb{C}_0\cup\{\infty\})}\), are not all real (unless \({\alpha_n}\) is real), and hence, they are not suitable to construct a rational Gaussian quadrature rule (RGQ). For this reason, the zeros of a so-called quasi-ORF or a so-called para-ORF are used instead. These zeros depend on one single parameter \({\tau\in(\mathbb{C}\cup\{\infty\})}\), which can always be chosen in such a way that the zeros are all real and simple. In this paper we provide a generalized eigenvalue problem to compute the zeros of a quasi-ORF and the corresponding weights in the RGQ. First, we study the connection between quasi-ORFs, para-ORFs and ORFs. Next, a condition is given for the parameter τ so that the zeros are all real and simple. Finally, some illustrative and numerical examples are given.
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This work is partially supported by the Belgian Network DYSCO (Dynamical Systems, Control, and Optimization), funded by the Interuniversity Attraction Poles Programme, initiated by the Belgian State, Science Policy Office. The scientific responsibility rests with its authors.
K. Deckers is a Postdoctoral Fellow of the Research Foundation, Flanders (FWO).
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Deckers, K., Bultheel, A. & Van Deun, J. A generalized eigenvalue problem for quasi-orthogonal rational functions. Numer. Math. 117, 463–506 (2011). https://doi.org/10.1007/s00211-010-0356-x
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DOI: https://doi.org/10.1007/s00211-010-0356-x