Abstract
We obtain new inequalities of different metrics for differentiable periodic functions. In particular, for p, q ∈ (0, ∞], q > p, and s ∈ [p, q], we prove that functions \(x \in L_\infty ^{{\text{ }}r}\) satisfy the unimprovable inequality
where ϕ r is the perfect Euler spline of order r and c s + 1(x) is the constant of the best approximation of the function x in the space L s + 1. By using the inequality indicated, we obtain a new Bernstein-type inequality for trigonometric polynomials τ whose degree does not exceed n, namely,
where k ∈ N, p ∈ (0, 1], and q ∈ [1, ∞]. We also consider other applications of the inequality indicated.
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REFERENCES
B. Sz.-Nagy, “Ñber Integralungleichungen zwischen einer Function und ihrer Ableitung,” Acta Sci. Math. 10, 64-74 (1941).
V. F. Babenko, V. A. Kofanov, and S. A. Pichugov, “Inequalities of Kolmogorov type and some of their applications in approximation theory,” Rend. Circ. Mat. Palermo, Ser. II, Suppl. 52, 223-237 (1998).
V. F. Babenko, V. A. Kofanov, and S. A. Pichugov, “Sz.-Nagy-type inequalities for periodic functions,” in: Abstracts of the International Conference “Approximation Theory and Harmonic Analysis,” Tula (1998), p. 29.
V. F. Babenko, V. A. Kofanov, and S. A. Pichugov, “Sz.-Nagy-type inequalities for periodic functions,” in: Proceedings of the International Scientific Conference “Contemporary Problems in Mathematics” (Chernivtsi) Part 1, Kiev (1998), pp. 9-11.
V. F. Babenko, V. A. Kofanov, and S. A. Pichugov, “Sz.-Nagy-type inequalities for periodic functions,” Dopov. NAN Ukr. No. 4, 7-10 (2000).
V. F. Babenko, V. A. Kofanov, and S. A. Pichugov, “Inequalities for norms of intermediate derivatives of periodic functions and their applications,” East J. Approxim. 3, No. 3, 351-376 (1997).
N. P. Korneichuk, Exact Constants in the Approximation Theory [in Russian], Nauka, Moscow (1987).
N. P. Korneichuk, V. F. Babenko, and A. A. Ligun, Extremal Properties of Polynomials and Splines [in Russian], Naukova Dumka, Kiev (1992).
V. V. Arestov, “On integral inequalities for trigonometric polynomials and their derivatives,” Izv. Akad. Nauk SSSR, Ser. Mat. 45, No. 1, 3-32 (1982).
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Kofanov, V.A. Inequalities of Different Metrics for Differentiable Periodic Functions, Polynomials, and Splines. Ukrainian Mathematical Journal 53, 685–700 (2001). https://doi.org/10.1023/A:1012522115312
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DOI: https://doi.org/10.1023/A:1012522115312