Convergence rate of spherical harmonic expansions of smooth functions

We extend a well-known result of Bonami and Clerc on the almost everywhere (a.e.) convergence of Cesàro means of spherical harmonic expansions. For smooth functions measured in terms of φ-derivatives on the unit sphere, we obtained the sharp a.e. convergence rate of Cesàro means of their spherical harmonic expansions.     

Almost Everywhere Convergence of Orthogonal Expansions of Several Variables

For a weighted L¹ space on the unit sphere of R^d+1, in which the weight functions are invariant under finite reflection groups, a maximal function is introduced and used to prove the almost everywhere convergence of orthogonal expansions in h-harmonics. The result applies to various methods of summability, including the de La Vallée Poussin means and the Cesàro means. Similar results are also established for weighted orthogonal expansions on the unit ball and on the simplex of R^d.     

Two-weight norm inequalities for the Cesàro means of Hermite expansions

An accurate estimate is obtained of the Cesàro kernel for Hermite expansions. This is used to prove two-weight norm inequalities for Cesàro means of Hermite polynomial series and for the supremum of these means. These extend known norm inequalities, even in the single power weight and ``unweighted' cases. An almost everywhere convergence result is obtained as a corollary. It is also shown that the conditions used to prove norm boundedness of the means and most of the conditions used to prove the boundedness of the Cesàro supremum of the means are necessary.

     

On Sign Distribution in Relatively Convergent Series

We study conditions of convergence of series with alternating signs. This problem has already attracted attention of many authors; among the most prominent let us mention Cesàro who first discovered even distributionof positive and negative terms in such series. This observation has been rediscovered and reproved by many authors. One of the goals of this paper is to show that Cesàro's result is indeed the best possible. In order to achieve this we introduce several quite sophisticated constructions of series with desired properties. The other goal is to get an interesting generalization of Cesàro's result by introducing the notion of logarithmic density (and then further generalizing it).     

Convergence rate of Fourier–Laplace series of L-functions

The almost everywhere convergence rates of Fourier–Laplace series are given for functions in certain subclasses of L²(Σ_n−1) defined in terms of moduli of continuity.     

On the Approximation of Bounded Functions with Discontinuities of the First Kind by Generalized Shepard Operators

The authors investigate the approximation of bounded functions with discontinuities of the first kind by generalized Shepard operators. Estimate for the rate of convergence at a continuity point is obtained, while at the points of discontinuity it is shown that the sequence of generalized Shepard operators is almost always divergent. It is also shown that the sequence of Cesàro means of generalized Shepard operators is convergent everywhere for bounded functions which have only discontinuities of the first kind in [0,1].     

Uniqueness for Cesàro summable double Walsh series

We prove a Tauberian theorem for Walsh series of two variables, and use it to obtain several results about uniqueness of Cesàro summable double Walsh series. Namely, we show that up to sets of measure zero, Cesàro summability of double Walsh series is the same as convergence of the square dyadic partial sums and, under a suitable growth condition, that uniqueness holds for Cesàro summable double Walsh series.     

Rate of Cesàro summability of double orthogonal series

Unimprovable estimates (in the class of double orthogonal series) are obtained on the rate of almost everywhere summability of orthogonal expansions of square-integrable functions by Cesàro methods of positive order. The conditions imposed on the coefficients are of classical type.     

The principle of general localization on unit sphere

In this paper we study the general localization principle for Fourier-Laplace series on unit sphere SN⊂RN+1. Weak type (1,1) property of maximal functions is used to establish the estimates of the maximal operators of Riesz means at critical index . The properties Jacobi polynomials are used in estimating the maximal operators of spectral expansions in L₂(SN). For extending positive results on critical line , 1?p?2, we apply interpolation theorem for the family of the linear operators of weak types. The generalized localization principle is established by the analysis of spectral expansions in L₂. We have proved the sufficient conditions for the almost everywhere convergence of Fourier-Laplace series by Riesz means on the critical line.     

Harmonic and Logarithmic Summability of Orthogonal Series are Equivalent up to a Set of Measure Zero

We prove Tauberian theorems from J_p-summability methods of powerseries type to ordinary convergence, respectively M_p-summabilitymethods of weighted means. Particular cases are the Abel andCesàro, as well as logarithmic and harmonic summability.Besides numerical series, we also consider orthogonal serieswith coefficients from L₂. In the latter case, it turns outthat one of our Tauberian conditions is satisfied almost everywhereon the underlying measure space, thereby proving the claim statedin the title.     

On the James constant and B-convexity of Cesàro and Cesàro-Orlicz sequence spaces

The classical James constant and the nth James constants, which are measure of B-convexity for the Cesàro sequence spaces cesp and the Cesàro-Orlicz sequence spaces cesM, are calculated. These investigations show that cesp,cesM are not uniformly non-square and even they are not B-convex. Therefore the classical Cesàro sequence spaces cesp are natural examples of reflexive spaces which are not B-convex. Moreover, the James constant for the two-dimensional Cesàro space is calculated.     

DIFFERENCES OF ERGODIC AVERAGES FOR CESARO BOUNDED OPERATORS

We prove that the weighted differences of ergodic averages,induced by a Cesàro bounded, strongly continuous, one-parametergroup of positive, invertible, linear operators on L^p, 1 <p < , converge almost every where and in the L^p-norm. Weobtain first the boundedness of the ergodic maximal operatorand the convergence of the averages.     

On the degree of approximation of functions belonging to a Lipschitz class by Hausdorff means of its fourier series

In a recent paper Lal and Yadov [4] obtained a theorem on the degree of approximation for a function belonging to the Lipschitz class Lipα using the product of the Cesàro and Euler means of order one of its Fourier series. In this paper we extend this result to any regular Hausdorff matrix for the same class of functions.     

The surprising almost everywhere convergence of Fourier-Neumann series

For most orthogonal systems and their corresponding Fourier series, the study of the almost everywhere convergence for functions in L^p requires very complicated research, harder than in the case of the mean convergence. For instance, for trigonometric series, the almost everywhere convergence for functions in L² is the celebrated Carleson theorem, proved in 1966 (and extended to L^p by Hunt in 1967).In this paper, we take the system

     

On the Libera operator

We show that the Libera operator, L, on some spaces of analytic functions is a continuous extension of the conjugate of the Cesàro operator. Results on L acting on various spaces are obtained. In particular, L maps the Bloch space into BMOA. We also prove some results on the best approximation by polynomials in Hardy and Bergman spaces.     

Complete convergence and Cesàro summation for i.i.d. random variables

Summary Various results generalizing summation methods for divergent series of real numbers to analogous results for independent, identically distributed random variables have appeared during the last two decades. The main result of this paper provides necessary and sufficient conditions for the complete convergence of the Cesàro means of i.i.d random variables.     

Convergence in measure of logarithmic means of quadratical partial sums of double Walsh-Fourier series

The main aim of this paper is to prove that the logarithmic means of quadratical partial sums of the double Walsh-Fourier series does not improve the convergence in measure. In other words, we prove that for any Orlicz space, which is not a subspace of LlnL(I²), the set of the functions having logarithmic means of quadratical partial sums of the double Walsh-Fourier series convergent in measure is of first Baire category.