Technical Report CS0510

Title: Quantitative and Constructive Aspects of the Generalized Koenig's and De Montessus's Theorems for Pade Approximants
Authors: Avram Sidi
Abstract: The generalized Koenig's theorem and de Montessus's theorem are two classical results concerning the convergence of the rows of the Pade table for meromorphic functions. Employing a technique that was recently developed for the analysis of vector extrapolation methods, refined versions of these theorems are proved in the present work. Specifically, complete expansions, for the numerators and denominators of Pade approximants are derived. These expansions are then used to obtain (1) precise asymptotic rates of convergence of the poles of the Pade approximants to the corresponding poles, simple or multiple, of the meromorphic function in question, and (2) the precise asymptotic behavior of the error in the relevant Pade approximants. One important feature of the asymptotic results derived in this work is that these are expressed in tenns of a very small number of parameters. Approximations of optimal accuracy to multiple poles and the principal parts of the corresponding Laurent expansions are also constructed.
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