关于积域上的粗糙奇异积分算子的一点注记

讨论积域上的奇异积分算子：ＴΩｆ（ｘ,ｙ） ＝ ｐ．ｖ．∫Ｒｎ×ＲｍΩ（ｕ,ｖ）｜ｕ｜ｎ｜ｖ｜ｍ ｆ（ｘ － ｕ,ｙ － ｖ）ｄｕｄｖ的Ｌｐ 有界性,及相应的Ｍａｒｃｉｎｋｉｅｗ ｉｃｚ积分的Ｌ２ 有界性． 其中Ω为类似文［４］中引进的函数类．     

一类离散型奇异积分算子

设｛αｋ｝∞ｋ＝－∞为正数缺项序列，满足ｉｎｆｋαｋ＋１／ｄｋ＝α＞１，Ω（ｙ′）为Ｂｅｓｏｖ空间Ｂ０，１１（Ｓｎ－１）上的函数，其中Ｓｎ－１为Ｒｎ（ｎ２）上的单位球面．本文证明：若∫Ｓｎ－１Ω（ｙ′）ｄσ（ｙ′）＝０，则离散型奇异积分ＴΩ（ｆ）（ｘ）＝∑∞ｋ＝－∞∫Ｓｎ－１ｆ（ｘ－αｋｙ′）Ω（ｙ′）ｄσ（ｙ′）和相关的极大算子ＴΩ（ｆ）（ｘ）＝ｓｕｐＮ∑∞ｋ＝Ｎ∫Ｓｎ－１ｆ（ｘ－αｋｙ′）Ω（ｙ′）ｄσ（ｙ′）均在Ｌ２（Ｒｎ）上有界．上述结果推广了Ｄｕｏａｎｄｉｋｏｅｔｘｅａ和ＲｕｂｉｏｄｅＦｒａｎｃｉａ［１］在Ｌ２情形下的一个结果     

关于丢番图方程x^2±2^m=y^n

本文证明了：方程ｘ２＋２ｍ＝ｙｎ，ｘ，ｙ，ｍ，ｎ∈Ｎ，ｇｃｄ（ｘ，ｙ）＝１，ｎ＞２仅有有限多组解（ｘ，ｙ，ｍ，ｎ），而且当（ｘ，ｙ，ｍ，ｎ）≠（５，３，１，３），（１１，５，２，３），（７，３，５，４）时，ｎ是适合ｎ≡７（ｍｏｄ８）以及２３≤ｎ＜８．５·１０６的奇素数，ｍａｘ（ｘ，ｙ，ｍ）＜Ｃ１；方程ｘ２－２ｍ＝ｙｎ，ｘ，ｙ，ｍ，ｎ∈Ｎ，ｇｃｄ（ｘ，ｙ）＝１，ｙ＞１；ｎ＞２仅有有限多组解（ｘ，ｙ，ｍ，ｎ），而且这些解都满足ｎ＜２·１０９炉以及ｍａｘ（ｘ，ｙ，ｍ）＜Ｃ２，这里Ｃ１，Ｃ２是可有效计算的绝对常数．     

半线性抛物型方程组Cauchy问题的一点注记

该文讨论Ｃａｕｃｈｒ问题整体光滑解的存在性，唯一性与渐近性，推广了文［２，３，１１，６，７，８，９］中相应的结果．这里ｕ＝（ｕ１，…，ｕｎ）Ｔ，Ａｉ（ｕ）（ｉ＝１，２，…，Ｎ）为ｎ×ｎ矩阵值函数，Ｄ为可对角化的ｎ×ｎ常数矩阵且其特征根大于０．     

A Restriction Theorem on the Reduced Product Heisenberg Group

§１．　ＩｎｔｒｏｄｕｃｔｉｏｎＬｅｔΩｂｅａｒｅｇｕｌａｒｃｏｎｅｉｎＲｎ,Φ：Ｃｍ×Ｃｍ→Ｃｎ＝Ｒｎ＋ｉＲｎａｎΩ－ｐｏｓｉｔｉｖｅＨｅｒｍｉｔｉａｎｍａｐ．ＴｈｅＳｉｅｇｅｌｄｏｍａｉｎＤΩ,ΦｏｆｔｙｐｅｔｗｏｉｎＣｎ×ＣｍｉｓｄｅｆｉｎｅｄｂｙＤΩ,Φ＝｛（ｚ,ｗ）∈：Ｃｎ×Ｃｍ：Ｉｍｚ－Φ（ｗ,ｗ）∈Ω｝（１）（ｓｅｅ［６］）．Ｓｐｅｃｉａｌｌｙ,ｗｅａｓｓｕｍｅｔｈａｔｎ＝ｍ,Ω＝｛ｔ＝（ｔ１,ｔ２,…,ｔｎ）∈Ｒｎ：ｔｉ＞０,ｉ＝１,２,…,ｎ｝,Φ（ｕ,ｖ）＝ｕ·ｖ＝（ｕ１ｕ…     

△^2u=λu＋N＋4／N—4＋μf（x）的多解存在性

讨论了非齐次双调和方程边值问题｛△＾２ｕ＝λｕ＋Ｎ＋４／ｕＮ－４＋ｕｆ（ｘ）,ｘ∈Ωｎ＝△ｕ｜ｎ＝０,的两个正解的存在性和非存在性,这里Ω是Ｒ＾Ｎ内有界光滑区域,Ｎ〉４,λ∈Ｒ＾１,μΠ０,ｆ（ｘ）是非负连续函数。     

一类椭圆方程很弱解关于区域的连续性

本文讨论了二阶椭圆型方程－Δｕ＝ｆ（ｘ,ｕ）,ｘ∈Ω的Ｄｉｒｉｃｈｌｅｔ问题ｕ｜Ω＝０的很弱解ｕ∈Ｗ０１,ｒ（Ω）（１＜ｒ＜２）关于区域Ω的连续性及很弱边值问题的很弱解的唯一性．     

多维非线性拟双曲方程外初边值问题

本文利用Ｌａｐｌａｃｅ方程解的正则性定理，建立一般非线性拟双曲型方程，Ｌ［ｕ］＝ｕｔｔ－Δｕｔ－ｎ／Σｉｊ＝１ａｉｊ（ｕＤｘｔｕ）Ｕｘｉｘｊ＋ｂ（ｕ，Ｄｘｔｕ）＝０的一个能量不等式和叠代格式，然后利用Ｓｏｂｏｌｅｘ空间中的弱紧性原理，证明方程（１）的外初边值问题古典整体解存在唯一性和衰减性质。     

一类n阶拟线性奇异摄动边值问题的一致有效渐近展开

本文研究一类ｎ阶拟线性奇异摄动边值问题：εｙ（ｎ）＝ｆ（ｔ，ε，ｙ，…，ｙ（ｎ－２）ｙ（ｎ－１）＋ｇ（ｔ，ε，ｙ，…，ｙ（ｎ－２），ｐｊ（ε）ｙ（ｊ）（０，ε）－ｑｊ（ε）ｙ（ｊ＋１）（０，ε）＝αｊ（ε）（０≤ｊ≤ｎ－２），ｂ１（ε）ｙ（ｎ－２）（１，ε）＋ｂ２（ε）ｙ（ｎ－１）（１，ε）＝β（ε），其中ε＞０为小参数．在较一般的条件之下，应用Ｂａｎａｃｈ／Ｐｉｃａｒｄ不动点定理证明了摄动解的存在性及局部唯一性，并给出了摄动解直到ｎ阶导函数的一致有效渐近展开式，推广和改进了已有的结果［１－５］．     

Volterra型积分微分方程非线性边值问题解的存在性和唯一性

本文利用上下解方法得到了带Ｖｏｌｔｅｒｒａ型积分算子的非线性边值问题，ｕ＾ｎ＝ｆ（ｔ，ｕ，ｕ′，Ｔｕ），ａ１ｕ（０）－ａ２ｕ′（０）＝Ａ，ｂ１ｕ（１）＋ｂ２ｕ′（１）＝Ｂ解的存在性和唯一性。     

The Mechanical Quadrature Methods and Their Extrapolation for Solving BIE of Steklov Eigenvalue Problems

By means of the potential theory Steklov eigenvalue problems are transformed into general eigenvalue problems of boundary integral equations (BIE) with the logarithmic singularity.Using the quadrature rules, the paper presents quadrature methods for BIE of Steklov eigenvalue problem, which possess high accuracies O(h^3) and low computing complexities. Moreover, an asymptotic expansion of the errors with odd powers is shown. Using h^3-Richardson extrapolation, we can not only improve the accuracy order of approximations, but also derive a posterior estimate as adaptive algorithms. The efficiency of the algorithm is illustrated by some examples.     

Shifted rectangular quadrature rule approximations to Dawson's integral F(x)

This paper investigates the relationship between some rapidly convergent series of exponential functions for computing Dawson's integral. These series are the result of approximating a certain improper integral by a shifted rectangular quadrature rule. Dawson's original method and a more recent expansion due to Rybicki are shown to be special cases of our quadrature approach. An error bound is derived to compare the accuracy of the resulting approximations.     

输运方程特征值问题的高精度求积方法

<正>1引言考虑平板各向异性散射和裂变的输运方程:其中,2a为平板厚度.-a≤x≤a,-1≤μ,μ′≤1,V是临界特征值.如何求解输运方程的最大的简单特征值问题是一个重要课题[1].关于它的存在性已     

A Certain Class of Weighted Approximations for Integrable Functions and Applications

A certain class of weighted approximations, which extends the results of Masjed-Jamei [6] is introduced for integrable functions and some of upper bounds are obtained for the absolute value of the errors of such approximations in two L¹[a, b] and L^∞[a, b] spaces. As the main motivation for introducing the aforesaid class, it is shown that many new inequalities can be generated from the given error bounds. Some illustrative examples are presented in this sense. Moreover, by using the obtained error bounds, a nonstandard type of three-point weighted quadrature rules is introduced and its error bounds are computed.     

An integral method for solving nonlinear eigenvalue problems

We propose a numerical method for computing all eigenvalues (and the corresponding eigenvectors) of a nonlinear holomorphic eigenvalue problem that lie within a given contour in the complex plane. The method uses complex integrals of the resolvent operator, applied to at least k column vectors, where k is the number of eigenvalues inside the contour. The theorem of Keldysh is employed to show that the original nonlinear eigenvalue problem reduces to a linear eigenvalue problem of dimension k. No initial approximations of eigenvalues and eigenvectors are needed. The method is particularly suitable for moderately large eigenvalue problems where k is much smaller than the matrix dimension. We also give an extension of the method to the case where k is larger than the matrix dimension. The quadrature errors caused by the trapezoid sum are discussed for the case of analytic closed contours. Using well known techniques it is shown that the error decays exponentially with an exponent given by the product of the number of quadrature points and the minimal distance of the eigenvalues to the contour.     

A fast algorithm for Gaussian type quadrature formulae with mixed boundary conditions and some lumped mass spectral approximations

After studying Gaussian type quadrature formulae with mixed boundary conditions, we suggest a fast algorithm for computing their nodes and weights. It is shown that the latter are computed in the same manner as in the theory of the classical Gauss quadrature formulae. In fact, all nodes and weights are again computed as eigenvalues and eigenvectors of a real symmetric tridiagonal matrix. Hence, we can adapt existing procedures for generating such quadrature formulae. Comparative results with various methods now in use are given. In the second part of this paper, new algorithms for spectral approximations for second-order elliptic problems are derived. The key to the efficiency of our algorithms is to find an appropriate spectral approximation by using the most accurate quadrature formula, which takes the boundary conditions into account in such a way that the resulting discrete system has a diagonal mass matrix. Hence, our algorithms can be used to introduce explicit resolutions for the time-dependent problems. This is the so-called lumped mass method. The performance of the approach is illustrated with several numerical examples in one and two space dimensions.

     

Discrete approximations to spherically symmetric distributions

Summary We consider the approximation of spherically symmetric distributions in ^d by linear combinations of Heaviside step functions or Dirac delta functions. The approximations are required to faithfully reproduce as many moments as possible. We discuss stable methods of computing such approximations, taking advantage of the close connection with Gauss-Christoffel quadrature. Numerical results are presented for the distributions of Maxwell, Bose-Einstein, and Fermi-Dirac.Dedicated to Fritz Bauer on the occasion of his 60th birthdayWork supported in part by the National Science Foundation under Grant MCS-7927158A1     

Computing Fresnel integrals via modified trapezium rules

In this paper we propose methods for computing Fresnel integrals based on truncated trapezium rule approximations to integrals on the real line, these trapezium rules modified to take into account poles of the integrand near the real axis. Our starting point is a method for computation of the error function of complex argument due to Matta and Reichel (J Math Phys 34:298–307, 1956) and Hunter and Regan (Math Comp 26:539–541, 1972). We construct approximations which we prove are exponentially convergent as a function of \(N\) , the number of quadrature points, obtaining explicit error bounds which show that accuracies of \(10^{-15}\) uniformly on the real line are achieved with \(N=12\) , this confirmed by computations. The approximations we obtain are attractive, additionally, in that they maintain small relative errors for small and large argument, are analytic on the real axis (echoing the analyticity of the Fresnel integrals), and are straightforward to implement.     

Fourier–Taylor Approximation of Unstable Manifolds for Compact Maps: Numerical Implementation and Computer-Assisted Error Bounds

We develop and implement a semi-numerical method for computing high-order Taylor approximations of unstable manifolds for hyperbolic fixed points of compact infinite-dimensional maps. The method can follow folds in the embedding and describes precisely the dynamics on the manifold. In order to ensure the accuracy of our computations in spite of the many truncation and round-off errors, we develop a posteriori error bounds for the approximations. Deliberate control of round-off errors (using interval arithmetic) in conjunction with explicit analytical estimates leads to mathematically rigorous computer-assisted theorems describing precisely the truncation errors for our approximation of the invariant manifold. The method is applied to the Kot-Schaffer model of population dynamics with spatial dispersion.     

Nonlinear Filtering of Diffusion Processes in Correlated Noise: Analysis by Separation of Variables

Abstract. An approximation to the solution of a stochastic parabolic equation is constructed using the Galerkin approximation followed by the Wiener chaos decomposition. The result is applied to the nonlinear filtering problem for the time-homogeneous diffusion model with correlated noise. An algorithm is proposed for computing recursive approximations of the unnormalized filtering density and filter, and the errors of the approximations are estimated. Unlike most existing algorithms for nonlinear filtering, the real-time part of the algorithm does not require solving partial differential equations or evaluating integrals. The algorithm can be used for both continuous and discrete time observations. \par