Approximation by Nörlund means of quadratical partial sums of double Walsh-Fourier series

In this article we discuss the Nörlund means of cubical partial sums of Walsh-Fourier series of a function in L ^p (1 ≤ p ≤ ∞). We investigate the rate of the approximation by this means, in particular, in Lip(α, p), where α > 0 and 1 ≤ p ≤ ∞. In case p = ∞ by L ^p we mean C _W , the collection of the uniformly W-continuous functions. Our main theorems state that the approximation behavior of the two-dimensional Walsh- Nörlund means is so good as the approximation behavior of the one-dimensional Walsh- Nörlund means. As special cases, we get the Nörlund logarithmic means of cubical partial sums of Walsh-Fourier series discussed recently by Gát and Goginava [5] in 2004 and the (C, β)-means of Marcinkiewicz type with respect to double Walsh-Fourier series discussed by Goginava [10]. Earlier results on one-dimensional Nörlund means of the Walsh-Fourier series was given by Móricz and Siddiqi [14].     

Convergence in measure of strong logarithmic means of double Fourier series

Nörlund strong logarithmic means of double Fourier series acting from space L log L \(\left( {\mathbb{T}^2 } \right)\) into space L _p \(\left( {\mathbb{T}^2 } \right)\) , 0 < p < 1, are studied. The maximal Orlicz space such that the Nörlund strong logarithmic means of double Fourier series for the functions from this space converge in two-dimensional measure is found.     

On the Nörlund logarithmic means with respect to Vilenkin system in the martingale Hardy space <Emphasis Type="Italic">H</Emphasis><Subscript>1</Subscript>

We prove and discuss a new divergence result of Nörlund logarithmic means with respect to Vilenkin system in Hardy space H ₁.     

Nörlund and Riesz mean of sequences of fuzzy real numbers

In this article we study some properties of the Nörlund and Riesz mean of sequences of fuzzy real numbers. We establish necessary and sufficient conditions for the Nörlund and Riesz means to transform convergent sequences of fuzzy numbers into convergent sequences of fuzzy numbers with limit preserving.     

Almost Everywhere Convergence of Strong Nörlund Logarithmic Means of Walsh-Fourier Series

In this paper we study the maximal operator for a class of subsequences of strong Nörlund logarithmic means of Walsh-Fourier series. For such a class we prove the almost everywhere strong summability for every integrable function f.     

On the progressive and nörlund means of re-arranged partial sums of a Fourier series

In this paper we give a relation between the progressive and Nörlund means for any non-negative and non-increasing sequence. We prove two generalizations of a theorem of Szàsz and give other parallel results for progressive and Nörlund means.     

On the Nörlund means of Vilenkin-Fourier series

We prove and discuss some new (H _p ,L _p )-type inequalities of weighted maximal operators of Vilenkin-Nörlund means with non-increasing coefficients {q _k : k ? 0}. These results are the best possible in a special sense. As applications, some well-known as well as new results are pointed out in the theory of strong convergence of such Vilenkin-Nörlund means. To fulfil our main aims we also prove some new estimates of independent interest for the kernels of these summability results.     

Uniform and L-convergence of Logarithmic Means of Walsh-Fourier Series

The （NSrlund） logarithmic means of the Fourier series of the integrable function f is： 1/lnn-1∑k=1Sk（f）/n-k, where ln：=n-1∑k=11/k. In this paper we discuss some convergence and divergence properties of this logarithmic means of the Walsh-Fourier series of functions in the uniform, and in the L^1 Lebesgue norm. Among others, as an application of our divergence results we give a negative answer to a question of Móricz concerning the convergence of logarithmic means in norm.     

Some inequalities involving upper bounds for some matrix operators I

In this paper we consider the problem of finding upper bounds of certain matrix operators such as Hausdorff, Nörlund matrix, weighted mean and summability on sequence spaces l _p(w) and Lorentz sequence spaces d(w, p), which was recently considered in [9] and [10] and similarly to [14] by Josip Pecaric, Ivan Peric and Rajko Roki. Also, this study is an extension of some works by G. Bennett on l _p spaces, see [1] and [2].     

Norm summability of Nörlund logarithmic means on unbounded Vilenkin groups

The (Nörlund) logarithmic means of the Fourier series is:

$t_n f = \frac{1}{{l_n }}\sum\limits_{k = 1}^{n - 1} {\frac{{S_k f}}{{n - k}}} , where l_n = \sum\limits_{k = 1}^{n - 1} {\frac{1}{k}} $

. In general, the Fejér (C,1) means have better properties than the logarithmic ones. We compare them and show that in the case of some unbounded Vilenkin systems the situation changes.

     

On generalized functional Nörlund methods

We discuss the relations between the convergence fields of the functional Nörlund methods (N, p, q, π) and (N, πr+ρp+p*r,q, πρ) in the ordinary and absolute case,p, q, r being suitable Lebesgue integrable functions and π, ρ∈?.     

On the divergence of Nörlund logarithmic means of Walsh-Fourier series

It is well known in the literature that the logarithmic means 1/logn ^n-1∑k=1 Sk（f）/k of Walsh or trigonometric Fourier series converge a.e. to the function for each integrable function on the unit interval. This is not the case if we take the partial sums. In this paper we prove that the behavior of the so-called NSrlund logarithmic means 1/logn ^n-1∑k=1 Sk（f）/n-k is closer to the properties of partial sums in this point of view.     

Zur Definition der Nörlundschen Hauptlösung von Differenzengleichungen

φ: R→R. Nörlund [4] defined the principal solution f_N of the difference equation $$V (x, y) \varepsilon R \times R_ + : \frac{1}{y}\left[ {g(x + y, y) - g(x, y)} \right] = \phi (x)$$ by V (x, y) ? [b, ∞) ×R₊: $$f_N (x, y) : = \mathop {\lim }\limits_{s \to 0 + } ( \int\limits_a^\infty {\phi (t) e^{ - st} dt} - y \sum\limits_{\nu = 0}^\infty { \phi (x + \nu y) e^{ - s(x + \nu y )} } )$$ with suitable a,bεR and proved the existence of f_N under certain restrictions onφ. In this paper, another way of defining a principal solution of the difference equation above, which includes Nörlund's, is gone. As an application, we construct in an easy manner a class of limitation methods for getting a principal solution, generalizing results from Nörlund [5].¹)     

Limitation theorems for absolute Nörlund summability

A limitation theorem concerning absolute Nörlund summability was proved recently. In the present paper limitation theorems concerning |N, p, q| summability are proved and corresponding theorems for |E, δ|, |C, α|, |C, α, β|, \(\left| {\bar N,p_n } \right|\) , |N, p _n ^α| methods are deduced as special cases.     

Integrals of weighted maximal logarithmic kernels on bounded Vilenkin groups

The integrals of maximal Riesz and Nörlund kernels are infinite, so we have to use some weight function to “pull them back” to the finite. In this paper we give necessary and sufficient conditions for the weight function to get a finite integral on bounded Vilenkin groups. For our motivation we refer the readers to [4], [5], [6].     

Summability of Laguerre series at the pointx=0

In this paper, the authors prove a theorem on matrix summability of Laguerre series at the point x=0. Various results on Casàro, Nörlund and generalized Nörlund summability method have been deduced.     

On the integral of the product of four and more Bernoulli polynomials

In 1958, L.J. Mordell provided a formula for the integral of the product of two Bernoulli polynomials. He also remarked: “The integrals containing the product of more than two Bernoulli polynomials do not appear to lead to simple results.” In this paper, we provide explicit formulas for the integral of the product of r Bernoulli polynomials, where r is any positive integer. Many results in this direction, including those by Nörlund, Mordell, Carlitz, Agoh, and Dilcher, are special cases of the formulas given in this paper.     

Riesz transforms and multipliers for the Grushin operator

We show that Riesz transforms associated to the Grushin operator G = ?Δ ? |x|²～ _t ² are bounded on L ^p (? ⁿ⁺¹). We also establish an analogue of the Hörmander-Mihlin Multiplier Theorem and study Bochner-Riesz means associated to the Grushin operator. The main tools used are Littlewood-Paley theory and an operator-valued Fourier multiplier theorem due to L. Weis.     

On the uniform Nörlund summability of Fourier series

A general theorem on uniform Nörlund summability of Fourier series has been derived. Some known results become its special cases.     

Matrix summability of a factored Fourier series

This paper reports a result for proving a triangular matrix summability of a factored Fourier series by extending the theorem on Nörlund summability of a factored Fourier series att =x when ?(t)∈B.V in (0, π) due to Singh [4] (Indian J. Math. 9 227–236). The result generalizes the theorem of Varshney [5] (Proc. Am. Math. Soc. 10, 784–789) and that of Singh.