scholarly journals On multidimensional Jackson's theorem

2021 ◽  
pp. 30
Author(s):  
S.A. Pichugov
Keyword(s):  
Modulus Of Continuity ◽  
Periodic Functions ◽  
Linear Polynomial ◽  
Multiple Variables ◽  
Polynomial Methods ◽  
Methods Of Approximation

We have found the best linear polynomial methods of approximation of continuous periodic functions of multiple variables in uniform metric with concave modulus of continuity.

APPROXIMATIVE PROPERTIES OF ABEL–POISSON-TYPE OPERATORS ON THE GENERALIZED HÖLDER CLASSES

2021 ◽  
Vol 1 ◽  
pp. 76-83
Author(s):  
Yuri I. Kharkevich ◽  
◽  
Alexander G. Khanin ◽  
Keyword(s):  
Modulus Of Continuity ◽  
Applied Mathematics ◽  
Continuous Functions ◽  
Elliptic Type ◽  
Periodic Functions ◽  
French Mathematician ◽  
First Order ◽  
Function Classes ◽  
In The Beginning ◽  
Poisson Type

The paper deals with topical issues of the modern applied mathematics, in particular, an investigation of approximative properties of Abel–Poisson-type operators on the so-called generalized Hölder’s function classes. It is known, that by the generalized Hölder’s function classes we mean the classes of continuous -periodic functions determined by a first-order modulus of continuity. The notion of the modulus of continuity, in turn, was formulated in the papers of famous French mathematician Lebesgue in the beginning of the last century, and since then it belongs to the most important characteristics of smoothness for continuous functions, which can describe all natural processes in mathematical modeling. At the same time, the Abel-Poisson-type operators themselves are the solutions of elliptic-type partial differential equations. That is why the results obtained in this paper are significant for subsequent research in the field of applied mathematics. The theorem proved in this paper characterizes the upper bound of deviation of continuous -periodic functions determined by a first-order modulus of continuity from their Abel–Poisson-type operators. Hence, the classical Kolmogorov–Nikol’skii problem in A.I. Stepanets sense is solved on the approximation of functions from the classes by their Abel–Poisson-type operators. We know, that the Abel–Poisson-type operators, in partial cases, turn to the well-known in applied mathematics Poisson and Jacobi–Weierstrass operators. Therefore, from the obtained theorem follow the asymptotic equalities for the upper bounds of deviation of functions from the Hölder’s classes of order from their Poisson and Jacobi–Weierstrass operators, respectively. The obtained equalities generalize the known in this direction results from the field of applied mathematics.

scholarly journals Approximation by algebraic polynomials in metric spaces $L_{\psi}$

2013 ◽  
Vol 21 ◽  
pp. 3
Author(s):  
T.A. Agoshkova
Keyword(s):  
Modulus Of Continuity ◽  
Metric Spaces ◽  
Jackson Inequality ◽  
Algebraic Polynomials ◽  
Periodic Functions ◽  
Jackson Theorem ◽  
Approximation By Algebraic Polynomials

In the space $L_{\psi}[-1;1]$ of non-periodic functions with metric $\rho(f,0)_{\psi} = \int\limits_{-1}^1 \psi(|f(x)|)dx$, where $\psi$ is a function of the type of modulus of continuity, we study Jackson inequality for modulus of continuity of $k$-th order in the case of approximation by algebraic polynomials. It is proved that the direct Jackson theorem is true if and only if the lower dilation index of the function $\psi$ is not equal to zero.

scholarly journals The degree of approximation by positive operators on compact connected abelian groups

1982 ◽  
Vol 33 (3) ◽  
pp. 364-373 ◽  
Author(s):  
Walter R. Bloom ◽  
Joseph F. Sussich
Keyword(s):  
Rate Of Convergence ◽  
Modulus Of Continuity ◽  
Abelian Groups ◽  
Degree Of Approximation ◽  
Linear Operators ◽  
Test Functions ◽  
Periodic Functions ◽  
Quantitative Version ◽  
Approximation By Positive Operators ◽  
Korovkin’S Theorem

AbstractIn 1953 P. P. Korovkin proved that if (Tn) is a sequence of positive linear operators defined on the space C of continuous real 2 π-periodic functions and lim Tnf = f uniformly for f = 1, cos and sin, then lim Tnf = f uniformly for all f ∈ C. Quantitative versions of this result have been given, where the rate of convergence is given in terms of that of the test functions 1, cos and sin, and the modulus of continuity of f. We extend this result by giving a quantitative version of Korovkin's theorem for compact connected abelian groups.

scholarly journals Best Multiplier Approximation of Unbounded Periodic Functions in L_(p,∅_n ) (B),B=[0,2π] Using Discrete Linear Positive Operators

2020 ◽  
Vol 17 (3) ◽  
pp. 0882
Author(s):  
Saheb AL- Saidy ◽  
Naseif AL-Jawari ◽  
Ali Hussein Zaboon
Keyword(s):  
Modulus Of Continuity ◽  
Positive Operators ◽  
Periodic Functions ◽  
Linear Positive Operators

The purpose of this paper is to find the best multiplier approximation of unbounded functions in    –space by using some discrete linear positive operators. Also we will estimate the degree of the best multiplier approximation in term of modulus of continuity and the averaged modulus.

scholarly journals Inequalities of Jackson-Stechkin type for $B^2$-almost periodic functions

2012 ◽  
Vol 20 ◽  
pp. 60
Author(s):  
V.F. Babenko ◽  
S.V. Savela
Keyword(s):  
Modulus Of Continuity ◽  
Almost Periodic Functions ◽  
Generalized Modulus Of Continuity ◽  
Almost Periodic ◽  
Periodic Functions

We obtain sharp inequalities of the Jackson-Stechkin type for approximation of $B^2$-almost periodic functions, containing the generalized modulus of continuity.

scholarly journals Estimation of deviation of continuous $2\pi$-periodic functions from corresponding trigonometric polynomials of S.N. Bernstein's type

2021 ◽  
pp. 43
Author(s):  
N.Ya. Yatsenko
Keyword(s):  
Periodic Function ◽  
Trigonometric Polynomial ◽  
Modulus Of Continuity ◽  
Trigonometric Polynomials ◽  
Periodic Functions

We have established the estimation of deviation of continuous $2\pi$-periodic function $f(x)$ from the trigonometric polynomial of S.N. Bernstein's type that corresponds to it, by the modulus of continuity of the function $f(x)$.

scholarly journals Direct and strong converse inequalities for approximation with Fejér means

2020 ◽  
Vol 53 (1) ◽  
pp. 80-85
Author(s):  
Jorge Bustamante
Keyword(s):  
Modulus Of Continuity ◽  
Periodic Functions ◽  
Lebesgue Spaces ◽  
Fejér Means ◽  
Strong Converse ◽  
Approximation Of Periodic Functions

AbstractWe present upper and lower estimates of the error of approximation of periodic functions by Fejér means in the Lebesgue spaces {L}_{2{\pi }}^{p}. The estimates are given in terms of a K-functional for 1\le p\le \infty and in terms of the first modulus of continuity in the case 1\lt p\lt \infty . We pay attention to the involved constants.

scholarly journals Estimates of the error of interval quadrature formulas on some classes of differentiable functions

2020 ◽  
Vol 28 (1) ◽  
pp. 12
Author(s):  
V.P. Motornyi ◽  
D.A. Ovsyannikov
Keyword(s):  
Quadrature Formula ◽  
Modulus Of Continuity ◽  
Quadrature Formulas ◽  
Periodic Functions ◽  
Differentiable Functions ◽  
The Given

The exact value of error of interval quadrature formulas$$\int_0^{2\pi}f(t)dt -\frac{\pi}{nh}\sum_{k=0}^{n-1}\int_{-h}^hf(t+\frac {2k\pi}{n})dt = R_n(f;\vec{c_0};\vec{x_0};h)$$obtained for the classes $W^rH^{\omega} (r=1,2,...)$ of differentiable periodic functions for which the modulus of continuity of the  $r -$th derivative is majorized by the given modulus of continuity $\omega(t)$. This interval quadrature formula coincides with the rectangles formula for the Steklov functions $f_h(t)$ and is optimal for some important classes of functions.

Sign in / Sign up

Export Citation Format

Share Document