Negative result in pointwise 3-convex polynomial approximation

• Date: 2009
• Main Authors: Bondarenko, A. V., Gilewicz, J., Бондаренко, А. В., Гилевич, Я. Я.
• Format: Article
• Language: Russian; English
• Published: Institute of Mathematics, NAS of Ukraine 2009
• Online Access: https://umj.imath.kiev.ua/index.php/umj/article/view/3040
• Journal Title: Ukrains’kyi Matematychnyi Zhurnal

Let $Δ^3$ be the set of functions three times continuously differentiable on $[−1, 1]$ and such that $f'''(x) ≥ 0,\; x ∈ [−1, 1]$. We prove that, for any $n ∈ ℕ$ and $r ≥ 5$, there exists a function $f ∈ C^r [−1, 1] ⋂ Δ^3 [−1, 1]$ such that $∥f (r)∥_{C[−1, 1]} ≤ 1$ and, fo...