arXiv subjects

Doron S Lubinsky

Publications and source records attributed to Doron S Lubinsky.

3 recordsLinked to original sources

arXiv2007

A New Approach to Universality Limits involving Orthogonal Polynomials

We show how localization and smoothing techniques can be used to establish universality in the bulk of the spectrum for a fixed positive measure mu on [-1,1]. Assume that mu is a regular measure, and is absolutely continuous in an open interval containing some closed subinterval J of (-1,1). Assume that in J, the absolutely continuous component mu' is positive and continuous. Then universality in J for mu follows from universality for the classical Legendre weight. We also establish universality in an L_{p} sense under weaker assumptions on mu.

math.CA↗

arXiv2007

A New Approach to Universality at the Edge of the Spectrum

We show how localization and smoothing techniques can be used to establish universality at the edge of the spectrum for a fixed positive measure on [-1,1]. Assume that the measure is a regular measure, and is absolutely continuous in some closed neighborhood J of 1. Assume that in J, w = h * Jacobi, where h(1)>0 and h is continuous at 1. Then universality at 1 for ourgiven measure follows from universality at 1 for the classical Jacobi weight. Note that no smoothness is required of h, only continuity.

math.CA↗

arXiv2007

A Survey of Weighted Approximation for Exponential Weights

Let W: R to (0,1] be continuous. Bernstein's approximation problem, posed in 1924, deals with approximation by polynomials in the weighted uniform norm ||fW|| Linfinity(R) . The qualitative form of this problem was solved by Achieser, Mergelyan, and Pollard, in the 1950's. Quantitative forms of the problem were actively investigated starting from the 1960's. We survey old and recent aspects of this topic, including the Bernstein problem, weighted Jackson and Bernstein Theorems, Markov-Bernstein and Nikolskii inequalities, orthogonal expansions and Lagrange interpolation. We present the main ideas used in many of the proofs, and different techniques of proof, though not the full proofs. The class of weights we consider is typically even, and supported on the whole real line, so we exclude Laguerre type weights on [0,infinity). Nor do we discuss Saff's weighted approximation problem, nor the asymptotics of orthogonal polynomials.

math.CA↗