Abstract
Assume that f ∈ C[−1, 1] belongs to C[−1, 1] and changes its convexity at s > 1 different points y i, \(\overline {1,s} \), from (−1, 1). For n ∈ N, n ≥ 2, we construct an algebraic polynomial P n of order ≤ n that changes its convexity at the same points y i as f and is such that
where ω3(f; t) is the third modulus of continuity of the function f and C(Y) is a constant that depends only on \(\mathop {\min }\limits_{i = 0,...,s} \left| {y_i - y_{i + 1} } \right|,\;\;y_0 = 1,\;\;y_{s + 1} = - 1\), y 0 = 1, y s + 1 = −1.
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Dzyubenko, H.A., Zalizko, V.D. Coconvex Approximation of Functions with More than One Inflection Point. Ukrainian Mathematical Journal 56, 427–445 (2004). https://doi.org/10.1023/B:UKMA.0000045688.71949.44
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DOI: https://doi.org/10.1023/B:UKMA.0000045688.71949.44