Kolmogorov-type inequalities for functions with asymmetric restrictions on the highest derivative

V.A. Kofanov (Oles Honchar Dnipro National University), https://orcid.org/0000-0003-0392-2257

Abstract


For $$$k, r\in {\rm \bf N}$$$, $$$k<r$$$; $$$q\ge 1$$$, $$$p>0$$$; $$$\alpha, \beta>0$$$ and for functions $$$x\in L_{\infty}^r({\rm\bf R})$$$ inequalities that estimate the norm $$$\|x_{\pm }^{(k)}\|_{L_q[a,b]}$$$ on an arbitrary segment $$$[a,b] \subset {\rm\bf R}$$$ such that $$$\;x^{(k)}(a)=x^{(k)}(b)=0$$$ via a local norm of the function $$$|||x^{\uparrow \downarrow}|||_p :=\sup \left\{ E_0(x)_{L_p[a,b]}: \; \pm x'(t) > 0 \; \forall t\in (a,b), \;\; a,b\in \rm \bf R \right\},$$$ and the asymmetric norm $$$\|\alpha^{-1}x_+^{(r)}+\beta ^{-1}x_-^{(r)}\| _{\infty}$$$ of its highest derivative are proved, where $$$E_0(x)_{L_p([a,b])}:= \inf \{\|x - c\|_{L_p([a,b])}: c \in {\rm \bf R }\}$$$.
As a consequence, generalizations of a number of well-known Kolmogorov-type inequalities are obtained.


Keywords


sharp Kolmogorov-type inequality; asymmetric case; local norm

MSC 2020


41A17; 41A44; 42A05; 41A15

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References


Babenko V.F. "Researches of Dnipropetrovsk mathematicians on inequalities for derivatives of periodic functions and their applications", Ukrainian Math. J., 2000, 52(1): pp. 9-29. doi:10.1007/BF02514133

Kwong M.K., Zettl A. "Norm inequalities for derivatives and differences", Lecture notes in mathematics, Berlin: Springer-Verlag, 1993.

Babenko V.F., Kofanov V.A., Pichugov S.A. "Comparison of exact constants in inequalities for derivatives of functions defined on the real axis and a circle", Ukrainian Math. J., 2003; 55(5): pp. 699-711. doi:10.1023/B:UKMA.0000010250.39603.d4

Kofanov V.A. "Sharp inequalities of Bernstein and Kolmogorov type", East J. Approx., 2005; 11(2): pp. 131-145.

Kofanov V.A. "On sharp inequalities of Bernstein type for splines", Ukrainian Math. J., 2006; 58(10): pp. 1357-1367. doi:10.1007/s11253-006-0152-z

Kofanov V.A., Miropolskiy V.E. "On the best constants in inequalilies of Kolmogorov-type", East J. Approx., 2007; 13(4): pp. 455-466.

Ligun A.A. "Inequalities for upper bounds of functionals", Analysis Math., 1976; 2(1): pp. 11-40. doi:10.1007/BF02079905

Kofanov V.A. "Inequalities for derivatives in $$$L_p$$$ spaces", Ukrainian Math. J., 2008; 60(10): pp. 1338-1349. doi:10.1007/s11253-009-0152-x

Kofanov V.A. "Inequalities of various metrics for differentiable periodic functions", Ukrainian Math. J., 2015; 67(2): pp. 202-212. doi:10.1007/s11253-015-1076-2

Kofanov V.A. "Inequalities for derivatives of functions on the axis with asymmetrically bounded higher derivatives", Ukrainian Math. J., 2012; 64(5): pp. 721-736. doi:10.1007/s11253-012-0674-5

Kofanov V.A. "Bojanov–Naidenov problem for functions with asymmetric restrictions for the higher derivative", Ukrainian Math. J., 2019; 71(3): pp. 419-434. doi:10.1007/s11253-019-01655-2

Babenko V.F., Kofanov V.A. "Nonsymmetric approximation of classes of differentiable functions by algebraic polynomials in the mean", Analys. Math., 1988; 14(3): pp. 193-217. doi:10.1007/BF01906847

Kofanov V.A., Sydorovych K.D. "Strengthening the Comparison Theorem and Kolmogorov Inequality in the Asymmetric Case", Res. Math,, 2022; 30(1): pp. 30-38. doi:10.15421/242204

Kofanov V.A., Zhuravel A.V. "A sharp Remez type inequalities for the functions with asymmetric restrictions on the oldest derivative", Res. Math., 2023; 31(1): pp. 40-51. doi:10.15421/242304

Pinkus A., Shisha O. "Variations on the Chebyshev and $$$L^q$$$-Theories of Best Approximation", Journal of Approx. Theory, 1982; 35(2): pp. 148-168. doi:10.1016/0021-9045(82)90033-8

Hörmander L. "A new proof and a generalization of an inequality of Bohr", Math. Scand., 1954; 2: pp. 33-45. doi:10.7146/math.scand.a-10392

Ligun A.A. "On inequalities between norms of derivatives of periodic functions", Math. Notes, 1983; 33(3): pp. 196-199. doi:10.1007/BF01686326


Korneichuk N.P., Babenko V.F., Kofanov V.A., Pichugov S.A. Inequalities for derivatives and their applications, Naukova dumka, 2003.

Kofanov V.A. "Inequalities for norms of derivatives of non-periodic functions with non-symmetric constraints on higher derivatives", Res. Math., 2012; 20: pp. 99-105.

Babenko V.F. "Asymmetric extremal problems in approximation theory", Dokl. AN sssr, 1983; 269(3): pp. 521-524.

Korneichuk N.P., Babenko V.F., Ligun A.A. Extremum properties of polynomials and splines, Naukova dumka, 1992.

Kofanov V.A. "On sharp inequalities of Kolmogorov and Bernstein type", Pratsі Ukrajins'kogo matematychnogo kongresu (Approximation theory and Fourier analysis), 2001, Kyiv, 2002; pp. 84-99.




DOI: https://doi.org/10.15421/242421

  

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