Please use this identifier to cite or link to this item: http://hdl.handle.net/10525/2430

 Title: On Optimal Quadratic Lagrange Interpolation: Extremal Node Systems with Minimal Lebesgue Constant via Symbolic Computation Authors: Rack, Heinz-JoachimVajda, Robert Keywords: ExtremalInterpolation NodesLagrange InterpolationLebesgue ConstantMinimalOptimalPolynomialQuadraticQuantifier EliminationSymbolic Computation Issue Date: 2014 Publisher: Institute of Mathematics and Informatics Bulgarian Academy of Sciences Citation: Serdica Journal of Computing, Vol. 8, No 1, (2014), 71p-96p Abstract: We consider optimal Lagrange interpolation with polynomials of degree at most two on the unit interval [−1, 1]. In a largely unknown paper, Schurer (1974, Stud. Sci. Math. Hung. 9, 77-79) has analytically described the infinitely many zero-symmetric and zero-asymmetric extremal node systems −1 ≤ x1 < x2 < x3 ≤ 1 which all lead to the minimal Lebesgue constant 1.25 that had already been determined by Bernstein (1931, Izv. Akad. Nauk SSSR 7, 1025-1050). As Schurer’s proof is not given in full detail, we formally verify it by providing two new and sound proofs of his theorem with the aid of symbolic computation using quantifier elimination. Additionally, we provide an alternative, but equivalent, parameterized description of the extremal node systems for quadratic Lagrange interpolation which seems to be novel. It is our purpose to bring the computer-assisted solution of the first nontrivial case of optimal Lagrange interpolation to wider attention and to stimulate research of the higher-degree cases. This is why our style of writing is expository. Description: ACM Computing Classification System (1998): G.1.1, G.1.2. URI: http://hdl.handle.net/10525/2430 ISSN: 1312-6555 Appears in Collections: Volume 8 Number 1

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