
The problem of finding the polynomial with minimal uniform norm on \({\mathcal E}_ r\) among all polynomials of degree at most \(n\) and normalized to be 1 at \(c\) is considered. Here \({\mathcal E}_ r\) is a given ellipse with both foci on the real axis and \(c\) is a given real point not contained in \({\mathcal E}_ r\). \textit{A. J. Clayton} [UKAEA Memorandum, AEEW, M 348 (1963)] proved that the unique optimal polynomial \(p_ n(z,r,c)\) is just the polynomial \((t_ n(z,c)=T_ n(z)/T_ n(c)\), where \(T_ n(z)\) denotes the \(n\)-th Chebyshev polynomial. The author shows that the normalized Chebyshev polynomials \(t_ n\) are not always optimal and hence Clayton's result is not true in general. Moreover, sufficient conditions which guarantee that Chebyshev polynomials are optimal are given.
Best approximation, Chebyshev systems, constrained approximation problem, Mathematics(all), Numerical Analysis, Approximation by polynomials, Applied Mathematics, optimal polynomial, Chebyshev polynomial, Analysis
Best approximation, Chebyshev systems, constrained approximation problem, Mathematics(all), Numerical Analysis, Approximation by polynomials, Applied Mathematics, optimal polynomial, Chebyshev polynomial, Analysis
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