ON THE BERLINSKII'S THEOREM FOR CUBIC SYSTEMS

1 IntroductionIn [1]-[31, the Berlinskii's theorem of the distribution of critical pointsfor quadratic differential systems is extended to the general n--th differentialsystems with nZ finite critical points. For cubic systems with 9 critical pointswhich must be all elementary, i.e., saddles or antisaddles, there are possiblysix kinds of distributions of critical points, such as 6 -- 3, 5 -- 4, 5 -- 3 1, 4 4 1, 4 -- 3 2 and 3 -- 3 3. For example, "5 -- 3 1" means that 5 outmostcriti…     

COMBINED LEGENDRE SPECTRAL-FINITE ELEMENT METHOD FOR THE TWO-DIMENSIONAL UNSTEADY NAVIER-STOKES EQUATION

1.IntroductionThereismuchliteratureconcerningnumericalsolutionsofNavier-Stokesequations,e.g.,see[1--4].FOrsemi-periodicproblems,someauthorusedcombinedFOurierspectralfinitedifferenceandFOurierspectral--finiteelementapproximations(see[5--8]).Influiddyn...     

GLOBAL CONVERGENCE OF QPFTH METHOD FOR LARGE-SCALE NONLINEAR SPARSE CONSTRAINED OPTIMIZATION

1.IntroductionIn[6],aQPFTHmethodwasproposedforsolvingthefollowingnonlinearprogrammingproblemwherefunctionsf:R"-- RIandgi:R"-- R',jeJaretwicecontinuouslydifferentiable.TheQPFTHalgorithmwasdevelopedforsolvingsparselarge-scaleproblem(l.l)andwastwo-stepQ-quadraticallyandR-quadraticallyconvergent(see[6]).Theglobalconvergenceofthisalgorithmisdiscussedindetailinthispaper.Forthefollowinginvestigationwerequiresomenotationsandassumptions.TheLagrangianofproblem(1.1)isdefinedbyFOundationofJiangs…     

A NEW EXTENSION OF THE HIGH-ORDER VIRASORO ALGEBRA

1 IntroductionVirasoro algebra and W algebra have been widely investigated by both physicists andmahematicians. Virasoro algebra can be thought of as the central extended algebra Of diffeOmorphisms Di$S') on the circle S1. In Ref[1], ftaPpat et al. extended the notion ofloop algebra g(S') to algebra g(M), M being a closed surface with dim M > 1, and gave thefolowing commutation relations:c,[Lk,l, L.,.] = [mp(k -- T) -- ftO(l -- 8)]Lk .,l , ti ll ghO(k -- j) -- fl0(l -- j)lok .,O8l ,,…     

三角中存在性问题的求解策略

解决存在性问题,对观察、联想、类比、猜测、抽象、概括诸方面有较高要求,高考题中一般对这类问题有如下方法:(1)直接求解;(2)观察--猜测--证明;(3)数形结合;(4)联想类比;(5)特殊--一般--特殊.现就三角中存在性问题选解几例.……     

拟半(E,F)}——凸函数及拟半(E,F)——凸规划的性质

简、胡及唐等(Int. J. Pure Appl. Math., 2004, 14(4): 439-454)于2004年提出了拟半(E,F)--凸函数的概念. 本文进一步深入讨论拟半(E,F)--凸函数及与之相应的拟半(E,F)--凸规划的一些重要性质, 建立了此类广义凸性的若干重要结论.     

怎样促进学生建构变化率概念的意义——对两节变化率课的反思

1 引言 <普通高中数学课程标准(实验)>把"导数"安排在选修系列1中,基本的指导思想是"强调对导数本质的认识,不仅作为一种规则,更作为一种重要的思想、方法来学习"[1],为了体现这种思想,课程不是按照传统的极限--连续--导数--微分--积分的逻辑链条呈现,而是以变化率--导数--积分的顺序编排.     

含有中间幂等元满足同余条件的◇-富足半群

本文引入了--格林关系和--富足半群,研究了满足同余条件含有中间幂等元的--富足半群.利用具有中间幂等元的由幂等元生成的正则半群和◇-拟恰当半群建立了满足同余条件含有中间幂等元的◇-富足半群的结构.     

Some extremal properties of the integral of legendre polynomials

1. Introduction and Main ResultsDenote by Pn the set of algebraic polynomials of degree not exceeding n. LetX = {X = (xl,xz,...,x.). 1 = xl > xz >' > xtL--l > xtL = --l}, n 2 2and let for X E X.Erd6s in [21 raised the question of determining Y E X such thatReceived July 21, 1999.also conjectured that Y = Z satisfyingw,,(Z, x) = c1' l" Pt.--1 (x) dx,j-- 1 Pt.-- 1 (x) dx,1 .2>where P,--1 stands for the (n -- 1)th Legendre polynomial normalized by Pn--1 (1) = l. Thiscolljecture was di…     

PERIODIC SOLUTIONS OF DELAY DIFFERENTIAL EQUATIONS WITH TWO DELAY VIA BI-HAMILTONIAN SYSTEMS

1 Illtroduction and Statement of the Main ResultIn this paper, we shall study the existence of periodic solutions for the twofOllowing differential delay equationsX'(t) = --f(x(t -- r1))g(x(t -- r2)) -- f(x(t -- r2))g(x(t -- r1)), (1)andX'(t) = f(x(t -- rl))g(x(t -- r2)) f(x(t -- r2))g(x(t -- rl)), (2)where ri (i = l,2) are positive constants. When the function g(x) = 1,equations (1) and (2) become respectivelyIn 1974, Kaplan and Yorke (see [101) proved the existence of periodic so1utions…     

ASYMPTOTIC ERROR EXPANSION AND DEFECT CORRECTION FOR SOBOLEV AND VISCOELASTICITY TYPE EQUATIONS

1.IntroductionLetObearectangulardomain.WeareconcernedwiththeRichardsonextrapolationanddefectcorrectionofthefiniteelementapproximationstothesolutionsofthefollowingsimpleSobolevtypeequationandviscoelasticitytypeequationTheextrapolationtechniqueusedforthefin…     

EXTRAPOLATION AND DEFECT CORRECTION FOR DIFFUSION EQUATIONS WITH BOUNDARY INTEGRAL CONDITIONS

1IntroductionIn[8],we11avestudiedparabolicintegrodifferentialequationswithhomogeneousboundaryconditionsbyextrapolatiollandcorrectionmethods,andderivedGalerkinapproximationsofthirdorder.Nowweturntodiffusionequationswithboundaryintegralconditions.Letfibearectangulardomain.Weareconcernedwitlltheapproximationtothesolutionofthemodelproblemwheren(x,y)=(m(x,y),"Z(x,y))istheouter--normaldirectiononoff.2GlobalExtrapolationFirstofall,wediscussextrpolationfortheproblem(1.l).Throughouttilepaper,weassum…     

特征值问题的三角形二次元的展开式及其外推

我们考虑利用三角形二次元来求解特征值问题,并给出特征值的误差展开式,以此为基础进行外推获得高精度.     

Extrapolation of Mixed Finite Element Approximations for the Maxwell Eigenvalue Problem

In this paper,a general method to derive asymptotic error expansion formulas for the mixed finite element approximations of the Maxwell eigenvalue problem is established.Abstract lemmas for the error of the eigenvalue approximations are obtained.Based on the asymptotic error expansion formulas,the Richardson extrapolation method is employed to improve the accuracy of the approximations for the eigenvalues of the Maxwell system from θ(h2) to θ(h4) when applying the lowest order Nédé1ec mixed finite element and a nonconforming mixed finite element.To our best knowledge,this is the first superconvergence result of the Maxwell eigenvalue problem by the extrapolation of the mixed finite element approximation.Numerical experiments are provided to demonstrate the theoretical results.     

外推瀑布多网格法(EXCMG)——-大规模求解椭圆问题的新算法

基于有限元的渐近展开式,导出了新的外推公式,它们更精确地逼近密网上的有限元解(而不是微分方程的解).提出了新的外推瀑布型多网格法(EXCMG),采用新外推公式及其二次插值提供密网上的好初值.数值实验表明,新方法有很高的精度和效率.最后在PC机上求解了大规模二维椭圆问题.     

Extrapolation of the Stochastic Theta Numerical Method for Stochastic Differential Equations

ABSTRACT

The stochastic theta method is a family of implicit Euler methods for approximating solutions to Itô stochastic differential equations. It is proved that the weak error for the stochastic theta numerical method is of the correct form to apply Richardson extrapolation. Several computational examples illustrate the improvement in accuracy of the approximations when applying extrapolation.     

On the extrapolation of Galerkin methods for parabolic problems

Summary The use of Richardson extrapolation in conjunction with several discrete-time Galerkin methods for the approximate solution of parabolic initialboundary value problems is investigated. It is shown that the extrapolation of certain two- and three-level Galerkin approximations which arep ^th order correct in time yields an improvement ofp orders of accuracy in time per extrapolation, wherep=1, 2. Both linear and quasilinear problems are considered.This research was supported in part by NSF Grant GP-36561.     

解平面弹性力学问题的边界积分方程的机械求积方法及其外推

１．引 言 考虑平面弹性力学内或外位移边值问题和内或外应力边值问题这里Ω是平面有界开集,Ωｃ是闭包Ω的补集,Γ是Ω或Ωｃ的边界,ｕ＝（ｕ１,ｕ２）是位移,ｎ＝（ｎ１,ｎ２）是Γ的外法向单位向量,δｉｊ＝（ｕｉ,ｊ＋ｕｊ,ｉ）／２是应变张量,λ和μ是Ｌａｍｅ常数,并且按张量计算规则：重复下标蕴含对该下标从１到２的求和． 使用直接边界元方法（１．１）与（１．２）皆可被转换为边界积分方程组这里αｉｊ（ｙ）是取决于ｙ∈Γ的常数,当ｙ是Γ的光滑点时,;式中是ｋｅｌｖｉｎ基本解,有以下表达式［５,７］这里ｒ＝…     

On improving the absolute stability of local extrapolation

Summary A widely used technique for improving the accuracy of solutions of initial value problems in ordinary differential equations is local extrapolation. It is well known, however, that when using methods appropriate for solving stiff systems of ODES, the stability of the method can be seriously degraded if local extrapolation is employed. This is due to the fact that performing local extrapolation on a low order method is equivalent to using a higher order formula and this high order formula may not be suitable for solving stiff systems. In the present paper a general approach is proposed whereby the correction term added on in the process of local extrapolation is in a sense a rational, rather than a polynomial, function. This approach allows high order formulae with bounded growth functions to be developed. As an example we derive anA-stable rational correction algorithm based on the trapezoidal rule. This new algorithm is found to be efficient when low accuracy is requested (say a relative accuracy of about 1%) and its performance is compared with that of the more familiar Richardson extrapolation method on a large set of stiff test problems.     

Asymptotic Expansions for Approximate Eigenvalues of Integral Operators with Nonsmooth Kernels

We consider approximation of eigenvalues of integral operators with Green's function kernels using the Nyström method and the iterated collocation method and obtain asymptotic expansions for approximate eigenvalues. We show that the Richardson extrapolation is applicable to find eigenvalue approximations of higher order and illustrate our results by numerical examples.