Integrability and <Emphasis Type="Italic">L</Emphasis><Superscript>1</Superscript>-convergence of double cosine trigonometric series

We study here L1-convergence of new modified double cosine trigonometric sum and obtain a new necessary and sufficient condition for L1-convergence of double cosine trigonometric series.Also,the results obtained by Moricz[1],[2] are particular cases of ours.     

Fast Wavelet Transform for Toeplitz Matrices and Property Analysis

Fast wavelet transform algorithms for Toeplitz matrices are proposed in this paper. Distinctive from the well known discrete trigonometric transforms, such as the discrete cosine transform （DCT） and the discrete Fourier transform （DFT） for Toeplitz matrices, the new algorithms are achieved by compactly supported wavelet that preserve the character of a Toeplitz matrix after transform, which is quite useful in many applications involving a Toeplitz matrix. Results of numerical experiments show that the proposed method has good compression performance similar to using wavelet in the digital image coding. Since the proposed algorithms turn a dense Toeplitz matrix into a band-limited form, the arithmetic operations required by the new algorithms are O（N） that are reduced greatly compared with O（N log N） by the classical trigonometric transforms.     

On Approximation of Function Classes in Lorentz Spaces with Anisotropic Norm

In this paper, Lorentz space of functions of several variables and Besov＇s class are considered. We establish an exact approximation order of Besov＇s class by partial sums of Fourier＇s series for multiple trigonometric system.     

On the laws of large numbers for double arrays of independent random elements in Banach spaces

For a double array of independent random elements {Vmn,m ≥ 1,n ≥ 1} in a real separable Banach space,conditions are provided under which the weak and strong laws of large numbers for the double sums mi=1 nj=1Vij,m ≥ 1,n ≥ 1 are equivalent.Both the identically distributed and the nonidentically distributed cases are treated.In the main theorems,no assumptions are made concerning the geometry of the underlying Banach space.These theorems are applied to obtain Kolmogorov,Brunk–Chung,and Marcinkiewicz–Zygmund type strong laws of large numbers for double sums in Rademacher type p(1 ≤ p ≤ 2) Banach spaces.     

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.     

On Incomplete Gaussian Sums

In his memior of 1837 on the existence of primes in a given arithmetic pro-gression, Dirichlet introduced what are now called Dirichlet's characters. Thesecharacters are arithmetic functions which are multiplicative and periodic. This paper deals with incomplete sums of the following type     

Optimal error estimates and modified energy conservation identities of the ADI-FDTD scheme on staggered grids for 3D Maxwell’s equations

This paper is concerned with the optimal error estimates and energy conservation properties of the alternating direction implicit finite-difference time-domain(ADI-FDTD) method which is a popular scheme for solving the 3D Maxwell’s equations.Precisely,for the case with a perfectly electric conducting(PEC) boundary condition we establish the optimal second-order error estimates in both space and time in the discrete H 1-norm for the ADI-FDTD scheme,and prove the approximate divergence preserving property that if the divergence of the initial electric and magnetic fields are zero,then the discrete L 2-norm of the discrete divergence of the ADI-FDTD solution is approximately zero with the second-order accuracy in both space and time.The key ingredient is two new discrete modified energy norms which are second-order in time perturbations of two new energy conservation laws for the Maxwell’s equations introduced in this paper.Furthermore,we prove that,in addition to two known discrete modified energy identities which are second-order in time perturbations of two known energy conservation laws,the ADI-FDTD scheme also satisfies two new discrete modified energy identities which are second-order in time perturbations of the two new energy conservation laws.This means that the ADI-FDTD scheme is unconditionally stable under the four discrete modified energy norms.Experimental results which confirm the theoretical results are presented.     

A LAW OF THE ITERATED LOGARITHM FOR NONPARAMETRIC CONDITIONAL DENSITY ESTIMATORS

We establish a law of the itearted logarithm for a triangular array of indepentent random variables, and apply it to obtain sharp pointwise rates of strong consistency for a large class of nonparametric estimators of bivariate density and conditional density. We consider the case of double kernel estimators anal trigonometric series estimators in detail.     

An Extension of the Turan Inequality in L_p-space for 0

周颂平 《数学研究与评论》1986,(2)

On quasi-convex mappings of orderαin the unit ball of a complex Banach space Dedicated to Professor Sheng GONG on the occasion of his 75th birthday

In this paper, a class of biholomorphic mappings named quasi-convex mapping of order a in the unit ball of a complex Banach space is introduced. When the Banach space is confined to Cn, we obtain the relation between this class of mappings and the convex mappings. Furthermore, the growth and covering theorems of this class of mappings are given on the unit ball of a complex Banach space X. Finally, we get the second order terms coefficient estimations of the homogeneous expansion of quasi-convex mapping of order a defined on the polydisc in Cn and on the unit ball in a complex Banach space, respectively.     

Double trigonometric series with positive coefficients

We present necessary and sufficient conditions for double sine, sinecosine, cosine-sine and double cosine series in terms of coefficients that their sums belong to double Lipschitz classes. Some classical results on single trigonometric series and some new results of Fülöp [2] on double trigonometric series are extended.     

Trigonometric sums over one-dimensional quasilattices of arbitrary codimension

A new class of one-dimensional quasilattices parametrized by the translations of the torus is introduced. For this class, parameter-dependent trigonometric sums over points of quasilattice are considered. Nontrivial estimates of the trigonometric sums under consideration are obtained. For a number of trigonometric sums of special form, asymptotic formulas are derived. It is proved that the distribution of points of quasilattices is uniform modulo h for almost all h. Earlier similar results were obtained in the particular case of quasilattices parametrized by the rotations of the circle.     

An extension of Vietoris's inequalities

We establish a best possible extension of a famous Theorem of Vietoris about the positivity of a general class of cosine sums. Our result refines and sharpens several earlier generalizations of this Theorem, and settles some open questions regarding the possibility of further improvement of it. Some new inequalities for trigonometric sums are given. We show that our results have applications within the context of positive sums of Gegenbauer polynomials and quadrature methods. We also obtain some existing estimates for the location of zeros of certain trigonometric polynomials under a weakened condition on their coefficients. 2000 Mathematics Subject ClassificationPrimary—42A05; Secondary—42A32,26D05, 26D15, 33B15, 33C45 Dedicated to Richard Askey on the occasion of his 70th birthday     

Consistent Riccati expansion for finding interaction solutions of (2+1)‐dimensional modified dispersive water‐wave system

A consistent Riccati expansion (CRE) is proposed to solve the (2+1)‐dimensional modified dispersive water‐wave (MDWW) system. It is proved that the MDWW system is CRE solvable. Furthermore, new exact interaction solutions, namely, soliton‐trigonometric waves, trigonometric waves‐soliton, soliton‐cosine periodic waves, and soliton‐cnoidal waves are explicitly derived.     

On Exponential Summability of Rectangular Partial Sums of Double Trigonometric Fourier Series

In this paper, we study the a.e. exponential strong summability problem for the rectangular partial sums of double trigonometric Fourier series of functions in L logL.     

Estimates from above of certain double trigonometric sums

In this paper we consider double trigonometric sums. Expressions of this type appear in some problems of quantum chaos and number theory. We are interested in rotation numbers of bounded type. We prove a uniform linear bound on double trigonometric sums along the subsequence of denominators of the continued fraction. The proof uses elementary techniques and the analysis of cancellations in sums of certain oscillatory functions over rotations. We also include a proof of a result on discrepancy for rotations of bounded type and in the Appendix we give an elementary proof of a result by Hardy and Littlewood.     

Trigonometric integrals over one-dimensional quasilattices of arbitrary codimension

The class of one-dimensional quasilattices parametrized by translations of the torus is studied. The trigonometric integrals averaging the moduli of trigonometric sums related to quasilattices are considered for this class. Nontrivial estimates of such integrals are obtained. The relationship between trigonometric integrals and several problems in the theory of Diophantine approximations is discussed.     

Double trigonometric sums and their application in approximating rational sums

Inequalities for double trigonometric sums are derived. These inequalities are used to obtain new estimates of incomplete rational trigonometrical sums with denominators equal to powers of rational numbers.Translated from Matematicheskie Zametki, Vol. 6, No. 1, pp. 25–34, July, 1969.     

Classes Lip(<Emphasis Type="Italic">α, p</Emphasis>) for double trigonometric series with monotone coefficients

The paper is devoted to the study of a connection between behavior of coefficients of double trigonometric series and the smoothness of their sums in the spaces L _p in the case when coefficients monotone decrease in each direction.