Generalized Taylor series for the class of functions H(ρ,m)

The nonquasianalytic class of functions H(, m) is constructively described by generalized Taylor series. Nonredundant discrete information in this connection is given with the help of first and second differences.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 42, No. 7, pp. 1007–1009, July, 1990.     

Basics of a generalized Wiman–Valiron theory for monogenic Taylor series of finite convergence radius

In this paper, we develop the basic concepts for a generalized Wiman–Valiron theory for Clifford algebra valued functions that satisfy inside an n + 1-dimensional ball the higher dimensional Cauchy-Riemann system ${\frac{\partial f}{\partial x_0} + \sum_{i=1}^n e_i\frac{\partial f}{\partial x_i}=0}In this paper, we develop the basic concepts for a generalized Wiman–Valiron theory for Clifford algebra valued functions that satisfy inside an n + 1-dimensional ball the higher dimensional Cauchy-Riemann system \frac?f?x₀ + ?_i=1ⁿ e_i\frac?f?x_i=0{\frac{\partial f}{\partial x_0} + \sum_{i=1}^n e_i\frac{\partial f}{\partial x_i}=0} . These functions are called monogenic or Clifford holomorphic inside the ball. We introduce growth orders, the maximum term and a generalization of the central index for monogenic Taylor series of finite convergence radius. Our goal is to establish explicit relations between these entities in order to estimate the asymptotic growth behavior of a monogenic function in a ball in terms of its Taylor coefficients. Furthermore, we exhibit a relation between the growth order of such a function f and the growth order of its partial derivatives.     

Hölder-continuity of certain generalized convex functions

It is proved that for a rationally s-convex function continuity and local s-Hölder - Continuity are equivalent at each interior point of the domain of definition of the function. Furthermore, it is shown that a rationally s-convex function which is bounded on a nonempty open convex set is s-Hölder-continuous on every compact subset of this set.     

Asymptotics of series arising from the approximation of periodic functions by Riesz and Cesàro means

Asymptotic expansions in powers of δ as δ → +∞ of the series $\sum\limits_{k = 0}^\infty {( - 1)^{(\beta + 1)k} \frac{{Q((\delta ^\alpha - (ak + b)^\alpha ) + )}} {{(ak + b)^{r + 1} }}} , $ where β ∈ ?, α, a, b > 0, and r ∈ ?, while Q is an algebraic polynomial satisfying the condition Q(0) = 0, are obtained. In special cases, these series arise from the approximation of periodic differentiable functions by the Riesz and Cesàro means.     

Asymptotics of diagonal Hermite–Padé polynomials for the collection of exponential functions

Mathematical Notes - In the paper, the semigroup of weak limits of the powers of an infinite transformation of rank one of Chacon type is completely described.     

Asymptotics of multipoint Hermite–Padé approximants of the first type for two beta functions

Mathematical Notes - The asymptotic behavior of the Hermite–Padé approximants of the first type for two beta functions are studied. The results are expressed in terms of equilibrium...     

Probability distribution functions of the Grincevi?jus series

Given a sequence (ξn,ηn) of independent identically distributed vectors of random variables we consider the Grincevi?jus series

     

On Taylor’s formula for functions of several variables

Elementary courses in mathematical analysis often mention some trick that is used to construct the remainder of Taylor’s formula in integral form. The trick is based on the fact that, differentiating the difference $f(x) - f(t) - f'(t)\frac{{(x - t)}} {{1!}} - \cdots - f^{(r - 1)} (t)\frac{{(x - t)^{r - 1} }} {{(r - 1)!}} $ between the function and its degree r ? 1 Taylor polynomial at t with respect to t, we obtain $ - f^{(r)} (t)\frac{{(x - t)^{r - 1} }} {{(r - 1)!}} $ , so that all derivatives of orders below r disappear. The author observed previously a similar effect for functions of several variables. Differentiating the difference between the function and its degree r ? 1 Taylor polynomial at t with respect to its components, we are left with terms involving only order r derivatives. We apply this fact here to estimate the remainder of Taylor’s formula for functions of several variables along a rectifiable curve.     

Summation of multiple trigonometric series by generalized methods formulated using δ -like finite functions

We consider the generalized sums of multiple trigonometric series. We investigate the sufficient conditions of convergence of the series obtained by termwise differentiation of the series for Lebesgue integrable functions as well as the errors of approximation of functions by sequences of generalized partial sums of series.     

Uniform convergence of rows of the Padé table for functions with smooth Maclaurin series coefficients

Given a formal power seriesf(z)?∑ _j=0 ^∞ a _j z ^j for which the quantitya _j ?1a _j +1/a _j ² has a prescribed asymptotic behavior asj→∞, we obtain the asymptotic behavior of poles of rows of the Padé table, and the associated Toeplitz determinants. In particular, we can show for large classes of entire functions of zero, finite, and infinite order (including the Mittag-Leffler functions) and forn=1,2,3,..., that the poles of [m/n](z) approach ∞ with ratea _m /a _m+1 asm→∞.     

A relaxed estimate of the degree of approximation by Fourier series in generalized Hölder metric

The aim of the paper is to give a relaxed estimate pertaining to the degree of approximation of the partial sums of Fourier series in a new Banach space of functions introduced by Das, Nath and Ray [2]. Furthermore, applying our new result, we verify, under certain natural conditions, that some classical means have the same approximation degree as the partial sums.     

Localization of Cesaro means of Fourier series for functions of bounded Λ-variation

We consider classes of periodic functions of bounded Λ-variation, where Λ has a power growth rate. We show that this class contains a continuous function whose Cesaro means of the Fourier series (whose order depends on the growth rate of Λ) have no localization property.     

Generalized factorization for a class of non-rational 2×2 matrix functions

In this paper the generalized factorization for a class of 2×2 piecewise continuous matrix functions on is studied. Using a space transformation the problem is reduced to the generalized factorization of a scalar piecewise continuous function on a contour in the complex plane. Both canonical and non-canonical generalized factorization of the original matrix function are studied.Sponsored by J.N.I.C.T. (Portugal) under grant no. 87422/MATM     

Examples of divergent fourier series for classes of functions of bounded Λ-variation

The author has shown earlier that the requirement that a continuous function belong to the class HBV ([?π, π] ^m ) for m ≥ 3 is not sufficient for the convergence of its Fourier series over rectangles. The author gave examples of functions of three and more variables from the Waterman class which are harmonic in the first variable and significantly narrower in the other variables and whose Fourier series are divergent at some point even on cubes. In the present paper, this assertion is strengthened. The main result is that such an example can be constructed even when the class with respect to the first variable is somewhat narrowed. Also the one-dimensional result due to Waterman is refined.     

Some test length bounds for nonrepeating functions in the {&;, ∨} basis

Testing relative to a nonrepeating alternative in a conjunction-disjunction basis is considered. A lower bound on the test length is established for all nonrepeating functions in this basis. A subsequence of easily testable functions is constructed and the corresponding tests are described. Individual lower test length bounds are proved for functions of a special form; minimality of the tests is established for the functions of the constructed subsequence.