
doi: 10.1007/bf01903676
Let \(C[a,b]\) be the space of continuous real-valued functions on \([a,b]\) with uniform norm \(\|\;\|\). For \(f\) in \(C[a,b]\), let \(B_ n(f)\) denote the best uniform approximate from the set of algebraic polynomials of degree \(n\) or less to \(f\). \(E_ n(f)\) is the number of the extremal points of \(f-B_ n(f)\). We define the local Lipschitz constant for \(f\) by \(\lambda^ \ell_ n(f)=\lim_{\delta\to+0}\sup\{\| B_ n(f+\varphi)-B_ n(f)\|/\|\varphi\|;\;0<\|\varphi\|<\delta\}\). Then Angelos, Henry, Kaufman, Kroó and Lenker showed that if \(E_ n(f)=n+2\) for all sufficiently large \(n\), \(\lim^ \lambda_ n(f)=\infty\). The authors study the behavior of \(\lambda^ \ell_ n(f)\) by using Kolushov polynomials. First they characterize \(\lambda^ \ell_ n(f)\) for fixed \(n\) in terms of Kolushov polynomials and second show that \(\lim \lambda^ \ell_ n(f)=\infty\) holds in the more general case.
Approximation by polynomials, local Lipschitz constant, algebraic polynomials, best uniform approximate, Kolushov polynomials
Approximation by polynomials, local Lipschitz constant, algebraic polynomials, best uniform approximate, Kolushov polynomials
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