We obtain exact Jackson-type inequalities in terms of the best approximations and averaged values of the generalized moduli of smoothness in the spaces \( {\mathcal{S}}^p \). For classes of periodic functions defined by certain conditions imposed on the average values of the generalized moduli of smoothness, we determine the exact values of the Kolmogorov, Bernstein, linear, and projective widths in the spaces \( {\mathcal{S}}^p \).
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F. Abdullayev, S. Chaichenko, and A. Shidlich, “Direct and inverse approximation theorems of functions in the Musielak–Orlicz type spaces,” Math. Inequal. Appl., 24, No. 2, 323–336 (2021).
F. G. Abdullayev, P. Özkartepe, V. V. Savchuk, and A. L. Shidlich, “Exact constants in direct and inverse approximation theorems for functions of several variables in the spaces \( {\mathcal{S}}^p \),” Filomat, 33, No. 5, 1471–1484 (2019).
N. Ainulloev, “Value of widths of some classes of differentiable functions in L2,” Dokl. Akad. Nauk Tadzh. SSR, 29, No. 8, 415–418 (1984).
V. F. Babenko and S. V. Konareva, “Jackson–Stechkin-type inequalities for the approximation of elements of Hilbert spaces,” Ukr. Mat. Zh., 70, No. 9, 1155–1165 (2018); English translation: Ukr. Math. J., 70, No. 9, 1331–1344 (2019).
J. Boman and H. S. Shapiro, “Comparison theorems for a generalized modulus of continuity,” Ark. Mat., 9, 91–116 (1971).
J. Boman, “Equivalence of generalized moduli of continuity,” Ark. Mat., 18, 73–100 (1980).
S. B. Vakarchuk, “Jackson-type inequalities and exact values of widths of classes of functions in the spaces Sp, 1 ≤ p < ∞,” Ukr. Mat. Zh., 56, No. 5, 595–605 (2004); English translation: Ukr. Math. J., 56, No. 5, 718–729 (2004).
S. B. Vakarchuk and A. N. Shchitov, “On some extremal problems in the theory of approximation of functions in the spaces Sp, 1 ≤ p < ∞,” Ukr. Mat. Zh., 58, No 3, 303–316 (2006); English translation: Ukr. Math. J., 58, No 3, 340–356 (2006).
S. B. Vakarchuk, “Jackson-type inequalities with generalized modulus of continuity and exact values of the n-widths for the classes of (ψ, β)-differentiable functions in L2. I,” Ukr. Mat. Zh., 68, No 6, 723–745 (2016); English translation: Ukr. Math. J., 68, No 6, 823–848 (2016).
S. N. Vasil’ev, “Jackson–Stechkin inequality in L2[−π, π],” in: Proc. of the Institute of Mathematics and Mechanics, Ural Division of the Russian Academy of Sciences, 7, No. 1, 75–84 (2001).
V. R. Voitsekhivs’kyi, “Jackson-type inequalities in the approximation of functions from the space Sp by Zygmund sums,” in: Proc. of the Institute of Mathematics, National Academy of Sciences of Ukraine, 35 (2002), pp. 33–46.
M. G. Esmanbetov, “Widths of the classes from L2[0, 2π] and minimization of exact constants in Jackson-type inequalities,” Mat. Zametki, 66, No. 6, 816–820 (1999).
A. I. Kozko and A.V. Rozhdestvenskii, “On the Jackson inequality in L2 with generalized modulus of continuity,” Mat. Sb., 195, No. 8, 3–46 (2004).
A. Pinkus, n-Widths in Approximation Theory, Springer, Berlin (1985).
V. V. Savchuk and A. L. Shidlich, “Approximation of functions of several variables by linear methods in the space Sp,” Acta Sci. Math. (Szeged), 80, No. 3-4, 477–489 (2014).
A. S. Serdyuk, “Widths in the space Sp of classes of functions defined by the moduli of continuity of their ψ-derivatives” in: Proc. of the Institute of Mathematics, National Academy of Sciences of Ukraine, 46 (2003), pp. 229–248.
A. I. Stepanets, “Approximating characteristics of the spaces \( {S}_{\varphi}^p \),” Ukr. Mat. Zh., 53, No. 3, 392–416 (2001); English translation: Ukr. Math. J., 53, No. 3, 446–475 (2001).
A. I. Stepanets, Methods of Approximation Theory, VSP, Leiden (2005).
A. I. Stepanets, “Problems of approximation theory in linear spaces,” Ukr. Mat. Zh., 58, No. 1, 47–92 (2006); English translation: Ukr. Math. J., 58, No. 1, 54–102 (2006).
A. I. Stepanets and A. S. Serdyuk, “Direct and inverse theorems in the theory of approximation of functions in the space Sp,” Ukr. Mat. Zh., 54, No. 1, 106–124 (2002); English translation: Ukr. Math. J., 54, No. 1, 126–148 (2002).
M. D. Sterlin, “Exact constants in inverse theorems of the approximation theory,” Dokl. Akad. Nauk SSSR, 202, No. 3, 545–547 (1972).
L. V. Taikov, “Inequalities containing best approximations and the modulus of continuity of functions from L2,” Mat. Zametki, 20, No. 3, 433–438 (1976).
L. V. Taikov, “Structural and constructive characteristics of functions from L2,” Mat. Zametki, 25, No. 2, 217–223 (1979).
V. M. Tikhomirov, Some Problems of Approximation Theory [in Russian], Moscow University, Moscow (1976).
M. F. Timan, Approximation and Properties of Periodic Functions [in Russian], Naukova Dumka, Kiev (2009).
N. I. Chernykh, “On the best approximation of periodic functions by trigonometric polynomials in L2,” Mat. Zametki, 2, No. 2, 513–522 (1967).
V. V. Shalaev, “Widths in L2 of classes of differentiable functions defined by higher-order moduli of continuity,” Ukr. Mat. Zh., 43, No. 1, 125–129 (1991); English translation: Ukr. Math. J., 43, No. 1, 104–107 (1991).
H. S. Shapiro, “A Tauberian theorem related to approximation theory,” Acta Math., 120, 279–292 (1968).
Kh. Yussef, “On the best approximations of functions and the values of widths of the classes of functions in L2,” in: Applications of Functional Analysis to the Approximation Theory, Proc. of the Tver Gos. Univ. (1988), pp. 100–114.
Kh. Yussef, “Widths of the classes of functions in the space L2(0, 2π),” in: Application of Functional Analysis to the Approximation Theory, Proc. of the Kalinin Gos. Univ. (1990), pp. 167–175.
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Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 73, No. 6, pp. 723–737, June, 2021. Ukrainian DOI: 10.37863/umzh.v73i6.6432.
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Abdullayev, F.G., Serdyuk, A.S. & Shidlich, A.L. Widths of Functional Classes Defined by the Majorants of Generalized Moduli of Smoothness in the Spaces \( {\mathcal{S}}^p \). Ukr Math J 73, 841–858 (2021). https://doi.org/10.1007/s11253-021-01963-6
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DOI: https://doi.org/10.1007/s11253-021-01963-6