On simultaneous approximation to a differentiable function and its derivative by Pál-type interpolation polynomials (Q1912656)

Let \(Q_n= Q_n (f, x)\) be the unique degree \(2n-1\) Pál type interpolating polynomial of a given function \(f\in \mathbb{C}^r\) over \([ -1,1 ]\). The first author [Chin. Ann. Math., Ser. B 9, No. 3, 315-321 (1988; Zbl 0672.41002)] improved an earlier estimate for \(f- Q_n\) due to \textit{S. A. N. Eneduanya} [Anal. Math. 11, 13-22 (1985; Zbl 0576.41005)]. A similar question for the derivative of \(f- Q_n\) is answered in the paper.