Weighted Approximation with Varying Weight

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This monograph offers a new construction for approximating a logarithmic potential by a discrete one. This yields a new approach to approximation with weighted polynomials of the form wn Pn. The new technique settles several open problems. It leads to a simple proof for the strong asymptotics on some Lp extremal problems on the real line with exponential weights, which, for the case p=2, are equivalent to power-type asymptotics for the leading coefficients of the corresponding orthogonal polynomials. The method is also modified to yield (in a sense) uniformly good approximation on the whole support. This allows the reader to deduce strong asymptotics in some Lp extremal problems with varying weights. Applications are given, relating to fast decreasing polynomials, asymptotic behaviour of orthogonal polynomials and multipoint Pade approximation.