Convergence of the Neumann Series in Higher Norms

Abstract

Natural conditions on an operator A are given so that the Neumann series for (Id + A)^?1 converges in higher norm topologies.     

On the coefficients of Neumann series of Bessel functions

Recently Pogány and Süli (Proc. Amer. Math. Soc. 137 (7) (2009) 2363-2368) derived a closed-form integral expression for Neumann series of Bessel functions. In this note we precisely characterize the class of functions α that generate the integral representation of a Neumann series of Bessel functions in the sense that the restriction αN_|=(αn) of a function α to the set N of all positive integers is the sequence of coefficients of the initial Neumann series.     

On the computation of highly oscillatory multivariate integrals with stationary points

We consider two types of highly oscillatory bivariate integrals with a nondegenerate stationary point. In each case we produce an asymptotic expansion and two kinds of quadrature algorithms: an asymptotic method and a Filon-type method. Our results emphasize the crucial role played by the behaviour at the stationary point and by the geometry of the boundary of the underlying domain. In memory of Germund Dahlquist (1925–2005). AMS subject classification (2000) Primary 65D32     

On Von Neumann Regular Rings of Skew Generalized Power Series

In this paper we introduce a construction called the skew generalized power series ring R[[S, ω]] with coefficients in a ring R and exponents in a strictly ordered monoid S which extends Ribenboim's construction of generalized power series rings. In the case when S is totally ordered or commutative aperiodic, and ω(s) is constant on idempotents for some s ∈ S?{1}, we give sufficient and necessary conditions on R and S such that the ring R[[S, ω]] is von Neumann regular, and we show that the von Neumann regularity of the ring R[[S, ω]] is equivalent to its semisimplicity. We also give a characterization of the strong regularity of the ring R[[S, ω]].     

On Quadrature Methods for Highly Oscillatory Integrals and Their Implementation

The main theme of this paper is the construction of efficient, reliable and affordable error bounds for two families of quadrature methods for highly oscillatory integrals. We demonstrate, using asymptotic expansions, that the error can be bounded very precisely indeed at the cost of few extra derivative evaluations. Moreover, in place of derivatives it is possible to use finite difference approximations, with spacing inversely proportional to frequency. This renders the computation of error bounds even cheaper and, more importantly, leads to a new family of quadrature methods for highly oscillatory integrals that can attain arbitrarily high asymptotic order without computation of derivatives. AMS subject classification (2000) Primary 65D30, secondary 34E05.Received June 2004. Accepted October 2004. Communicated by Lothar Reichel.     

基于修正的Magnus方法的高振荡动力系统的数值积分方法

基于建立于一般线性动力系统上的Magnus数值积分方法,针对随时间而高频率振荡的二阶动力系统,给出了有效的修正Magnus数值积分算法．首先,将二阶动力系统重新表示为一阶系统的形式,通过引进新变量进行参考坐标变换,使动力系统的高振荡性质保留在新形式内;进而基于局部线性化技术用修正的Magnus方法求解新形式下的系统方程;最后,通过一系列数值实验说明了文中方法的有效性．     

On the numerical quadrature of highly-oscillating integrals II: Irregular oscillators

In this paper we set out to understand Filon-type quadratureof highly-oscillating integrals of the form ₀¹ f(x) e^ig(x) dx,where g is a real-valued function and >> 1. Employingad hoc analysis, as well as perturbation theory, we demonstratethat for most functions g of interest the moments behave asymptoticallyaccording to a specific model that allows for an optimal choiceof quadrature nodes. Filon-type methods that employ such quadraturenodes exhibit significantly faster decay of the error for highfrequencies . Perhaps counterintuitively, as long as optimalquadrature nodes are used, rapid oscillation leads to significantlymore precise and more affordable quadrature.     

一类时滞双曲方程的振动准则

本文考虑一类滞量为连续分布型的双曲偏泛函微分方程解的振动性质，给出了这类方程在三类边值条件下解的振动准则．     

Adiabatic Integrators for Highly Oscillatory Second-Order Linear Differential Equations with Time-Varying Eigendecomposition

Numerical integrators for second-order differential equations with time-dependent high frequencies are proposed and analysed. We derive two such methods, called the adiabatic midpoint rule and the adiabatic Magnus method. The integrators are based on a transformation of the problem to adiabatic variables and an expansion technique for the oscillatory integrals. They can be used with far larger step sizes than those required by traditional schemes, as is illustrated by numerical experiments. We prove second-order error bounds with step sizes significantly larger than the almost-period of the fastest oscillations.AMS subject classification (2000) 65L05, 65L70.Received February 2004. Accepted February 2005. Communicated by Syvert Nørsett.     

On the Implementation of the Method of Magnus Series for Linear Differential Equations

The method of Magnus series has recently been analysed by Iserles and Nørsett. It approximates the solution of linear differential equations y = a(t)y in the form y(t) = e ^(t) y ₀, solving a nonlinear differential equation for by means of an expansion in iterated integrals of commutators. An appealing feature of the method is that, whenever the exact solution evolves in a Lie group, so does the numerical solution.The subject matter of the present paper is practical implementation of the method of Magnus series. We commence by briefly reviewing the method and highlighting its connection with graph theory. This is followed by the derivation of error estimates, a task greatly assisted by the graph-theoretical connection. These error estimates have been incorporated into a variable-step fourth-order code. The concluding section of the paper is devoted to a number of computer experiments that highlight the promise of the proposed approach even in the absence of a Lie-group structure.     

Regularity for Fully Nonlinear Elliptic Equations with Neumann Boundary Data

We obtain local C ^α, C ^1,α, and C ^2,α regularity results up to the boundary for viscosity solutions of fully nonlinear uniformly elliptic second order equations with Neumann boundary conditions.     

求解二维不可压缩Navier-Stokes方程的混合型微分求积法

微分求积法（ＤＱＭ）能以较少的网格点求得微分方程的高精度数值解,但采用单纯的微分求积法求解二维不可压缩Ｎａｖｉｅｒ＿Ｓｔｏｋｅｓ 方程时,只能对低雷诺数流动获得较好的数值解,当雷诺数较高时会导致数值解不收敛·　为此,提出了一种微分求积法与迎风差分法混合求解二维不可压缩Ｎａｖｉｅｒ＿Ｓｔｏｋｅｓ 方程的预估＿校正数值格式,用伪时间相关算法以较少的网格点获得了较高雷诺数流动的数值解·　作为算例,对１∶１ 和１∶２ 驱动方腔内的流动进行了计算,得到了较好的数值结果·     

p-Laplace方程Neumann边值问题的可解性

主要讨论了一维p-Laplace方程(φp(u′))′=f(t,u,u′),t∈(0,1))在Neumann边值条件u′(0)=0,u′(1)=0下边值问题解的存在性,其中φp(s)=|s|p-2s,s≠0.文中通过使用Leray-Schauder度原理,在适当的条件下,建立了对于p-Laplace方程在共振情形下Neumann边值问题解的存在性的充分条件.     

高阶泛函微分方程的振动性质*

本文借助于Lebesgue测度等工具研究了一类高阶非线性泛函微分方程的振动性质.文中指出.在一定条件下,方程的非振动解仅有两类,而且给出了每一类非振动解存在的必要条件,同时也建立了方程振动的若干充分判据.     

On the Neumann problem for elliptic equations involving the p-Laplacian

The aim of this paper is to establish the existence of an unbounded sequence of weak solutions to a Neumann problem for elliptic equations involving the p-Laplacian.     

一类偏差分方程的振动性

主要研究了偏差分方程pu_(m+2),n+u_(m,n+2)+qu_(m+1,n)-u_(m,n+1)+ru_(m,n)=0,解的振动性,其中参数p,q,r是实数,m,n为非负整数.     

一阶中立型时滞微分方程的振动性

通过构造适当的变换及有效函数,研究了一阶中立型时滞微分方程[x(t)-c(t)x(t-r)]′+p(t)f(x(t-τ))+∑ni=1qi(t)}f(x(t-σi))=0的振动性,获得了此方程所有解振动的n族充分条件.     

Hessian型方程Neumann边值问题的梯度估计

通过构造辅助函数,利用基本对称函数的性质以及函数在极大值点的性质,得到Hessian型方程S_k(D~2u-A(x,u,Du))=B(x,u)的梯度内估计,构造不同的辅助函数,分近边、边界和内部3种情形讨论该方程Neumann边值问题,进而得到全局梯度估计.     

负系数差分方程的振动性质

研究了一类负系数差分方程的振动性质,得到了这类差分方程振动的判据.     

一类非线性中立型时滞差分方程的振动性

考虑变形数中立型时滞差分方程△（ｘｎ－∑ｔｉ＝１ｑｉ,ｎｆｉ（ｘｎ－ｍｉ）＝０,ｎ＝０,１,２,…建立了此方程所有解振动的一个充分条件。