Abstract
We find the decay orders of the Kolmogorov widths of some Besov classes related to \(W^1_1\) (the behavior of the widths for the class \(W^1_1\) remains unknown): \(d_n(B^1_{1,\theta}[0,1],L_q[0,1])\asymp n^{-1/2}\log^{\max\{1/2,1-1/\theta\}}n\) for \(2<q<\infty\) and \(1\le\theta\le\infty\). The proof relies on the lower bound for the width of a product of octahedra in a special norm (maximum of two weighted \(\ell_{q_i}\) norms). This bound generalizes B. S. Kashin’s theorem on the widths of octahedra in \(\ell_q\).
Similar content being viewed by others
References
E. S. Belinskii, “Approximation of periodic functions by a ‘floating’ system of exponentials, and trigonometric widths,” in Studies on the Theory of Functions of Many Real Variables (Yaroslav. Gos. Univ., Yaroslavl, 1984), pp. 10–24 [in Russian].
O. V. Besov, “Continuation of some classes of differentiable functions beyond the boundary of a region,” Proc. Steklov Inst. Math. 77, 37–48 (1967) [transl. from Tr. Mat. Inst. Steklova 77, 35–44 (1965)].
R. A. DeVore and G. G. Lorentz, Constructive Approximation (Springer, Berlin, 1993), Grundl. Math. Wiss. 303.
D. Zung (Dung), “Approximation by trigonometric polynomials of functions of several variables on the torus,” Math. USSR, Sb. 59 (1), 247–267 (1988) [transl. from Mat. Sb. 131 (2), 251–271 (1986)].
D. Dũng, V. Temlyakov, and T. Ullrich, Hyperbolic Cross Approximation (Birkhäuser, Cham, 2018).
E. M. Galeev, “Kolmogorov widths of classes of periodic functions of one and several variables,” Math. USSR, Izv. 36 (2), 435–448 (1991) [transl. from Izv. Akad. Nauk SSSR, Ser. Mat. 54 (2), 418–430 (1990)].
E. M. Galeev, “Widths of the Besov classes \(B^r_{p,\theta }(\mathbb T^d)\),” Math. Notes 69 (5–6), 605–613 (2001) [transl. from Mat. Zametki 69 (5), 656–665 (2001)].
G. Garrigós, A. Seeger, and T. Ullrich, “Basis properties of the Haar system in limiting Besov spaces,” in Geometric Aspects of Harmonic Analysis (Springer, Cham, 2021), Springer INdAM Ser. 45; arXiv: 1901.09117 [math.CA].
D. Haroske and L. Skrzypczak, “Entropy and approximation numbers of embeddings of function spaces with Muckenhoupt weights. I,” Rev. Mat. Complut. 21 (1), 135–177 (2008).
R. S. Ismagilov, “On \(n\)-dimensional diameters of compacts in a Hilbert space,” Funct. Anal. Appl. 2 (2), 125–132 (1968) [transl. from Funkts. Anal. Prilozh. 2 (2), 32–39 (1968)].
B. S. Kashin, “On certain properties of matrices of bounded operators from the space \(\ell _2^n\) into \(\ell _2^m\),” Izv. Akad. Nauk Arm. SSR, Mat. 15 (5), 379–394 (1980).
B. S. Kashin, Yu. V. Malykhin, and K. S. Ryutin, “Kolmogorov width and approximate rank,” Proc. Steklov Inst. Math. 303, 140–153 (2018) [transl. from Tr. Mat. Inst. Steklova 303, 155–168 (2018)].
E. D. Kulanin, “On the diameters of a class of functions of bounded variation in the space \(L^q(0,1)\), \(2<q<\infty \),” Russ. Math. Surv. 38 (5), 146–147 (1983) [transl. from Usp. Mat. Nauk 38 (5), 191–192 (1983)].
G. G. Lorentz, M. von Golitschek, and Y. Makovoz, Constructive Approximation: Advanced Problems (Springer, Berlin, 1996).
Yu. V. Malykhin and K. S. Ryutin, “The product of octahedra is badly approximated in the \(\ell _{2,1}\)-metric,” Math. Notes 101 (1–2), 94–99 (2017) [transl. from Mat. Zametki 101 (1), 85–90 (2017)].
A. S. Romanyuk, “Approximation of the Besov classes of periodic functions of several variables in a space \(L_q\),” Ukr. Math. J. 43 (10), 1297–1306 (1991).
H. Triebel, Theory of Function Spaces. III (Birkhäuser, Basel, 2006), Monogr. Math. 100.
H. Triebel, Function Spaces and Wavelets on Domains (Eur. Math. Soc., Zürich, 2008), EMS Tracts Math. 7.
P. Wojtaszczyk, A Mathematical Introduction to Wavelets (Cambridge Univ. Press, Cambridge, 1997).
Funding
This work was supported by a grant of the Government of the Russian Federation (project no. 14.W03.31.0031).
Author information
Authors and Affiliations
Corresponding author
Additional information
Published in Russian in Trudy Matematicheskogo Instituta imeni V.A. Steklova, 2021, Vol. 312, pp. 224–235 https://doi.org/10.4213/tm4136.
Rights and permissions
About this article
Cite this article
Malykhin, Y.V. Kolmogorov Widths of the Besov Classes \(B^1_{1,\theta}\) and Products of Octahedra. Proc. Steklov Inst. Math. 312, 215–225 (2021). https://doi.org/10.1134/S0081543821010132
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1134/S0081543821010132