Abstract
LetE n (f) denote the sup-norm-distance (with respect to the interval [−1, 1]) betweenf and the set of real polynomials of degree not exceedingn. For functions likee x, cosx, etc., the order ofE n (f) asn→∞ is well known. A typical result is
It is shown in this paper that 2n−1 n!E n−1(e x) possesses a complete asymptotic expansion. This result is contained in the more general result that for a wide class of entire functions (containing, for example, exp(cx), coscx, and the Bessel functionsJ k (x)) the quantity
possesses a complete asymptotic expansion (providedn is always even (resp. always odd) iff is even (resp. odd)).
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Communicated by Edward B. Saff.
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Fiedler, H. On the asymptotic behavior of the bestL ∞-approximation by polynomials. Constr. Approx 3, 377–388 (1987). https://doi.org/10.1007/BF01890576
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DOI: https://doi.org/10.1007/BF01890576