A Survey of Weighted Polynomial Approximation with Exponential Weights

Abstract

Let W: R! (0, 1] be continuous. Bernstein's approximation problem, posed in 1924,deals with approximation by polynomials in the weighted uniform norm f! kfW kL1(R). Thequalitative 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. Wesurvey old and recent aspects of this topic, including the Bernstein problem, weighted Jackson and Bernstein Theorems, Markov-Bernstein and Nikolskii inequalities, orthogonal expansionsand 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 typicallyeven, and supported on the whole real line, so we exclude Laguerre type weights on [0, 1).Nor do we discuss Saff's weighted approximation problem, nor the asymptotics of orthogonal