THE SINGULARLY PERTURBED BOUNDARY VALUE PROBLEMS FOR HIGHER ORDER SEMILINEAR ELLIPTIC EQUATIONS

Considerasingularlyperturbedproblemforhigherorderselnilinearequationswhereeisasmallpositiveparameter,ndenotesaboundedregioninRe,whereonsignifiesasmoothboundaryofn,misaintegerandjk,gi,k,j=0,',in--1,aresufficientlysmoothfunctionswithregardtotheirvariablesincorrespondenceranges.Modealwiththesingularperturbationforthesecondorder'ellipticequations[1],[2],thefourthorderequations[3]l[4]andaclassofhigherorderequations[5].Inthispaperttheauthorsconsiderthesingularperturbationforevenmoregeneralhigheror…     

Sine transform based preconditioners for elliptic problems

We consider applying the preconditioned conjugate gradient (PCG) method to solving linear systems Ax = b where the matrix A comes from the discretization of second-order elliptic operators with Dirichlet boundary conditions. Let (L + Σ)Σ⁻¹(L^t + Σ) denote the block Cholesky factorization of A with lower block triangular matrix L and diagonal block matrix Σ. We propose a preconditioner M = (Lˆ + Σˆ)Σˆ⁻¹(Lˆ^t + Σˆ) with block diagonal matrix Σˆ and lower block triangular matrix Lˆ. The diagonal blocks of Σˆ and the subdiagonal blocks of Lˆ are respectively the optimal sine transform approximations to the diagonal blocks of Σ and the subdiagonal blocks of L. We show that for two-dimensional domains, the construction cost of M and the cost for each iteration of the PCG algorithm are of order O(n² log n). Furthermore, for rectangular regions, we show that the condition number of the preconditioned system M⁻¹A is of order O(1). In contrast, the system preconditioned by the MILU and MINV methods are of order O(n). We will also show that M can be obtained from A by taking the optimal sine transform approximations of each sub-block of A. Thus, the construction of M is similar to that of Level-1 circulant preconditioners. Our numerical results on two-dimensional square and L-shaped domains show that our method converges faster than the MILU and MINV methods. Extension to higher-dimensional domains will also be discussed. © 1997 John Wiley & Sons, Ltd.     

A Fully Nonlinear Boundary value Problem for the Laplace Equation in Dimension Two

We study the regularity up to the boundary of solutions to the boundary value problem:[math001] in D, ∣?u∣= g on &;pardD, where D is the unit disc. This problem finds its application in the study of geophysical and geomagnetic surveys. If g?C^,[math001](D) and is strictly positive, we prove that uis in the Holder class C1,α(D). An example shows that this is no longer true if g has some zeroes on ?D. In this case u isproved to be of class C¹(D)     

A Comparison of Splittings and Integral Equation Solvers for a Nonseparable Elliptic Equation

Iterative numerical schemes for solving the electrostatic partial differential equation with variable conductivity, using fast and high-order accurate direct methods for preconditioning, are compared. Two integral method schemes of this type, based on previously suggested splittings of the equation, are proposed, analyzed, and implemented. The schemes are tested for large problems on a square. Particular emphasis is paid to convergence as a function of geometric complexity in the conductivity. Differences in performance of the schemes are predicted and observed in a striking manner. AMS subject classification (2000) 31A10, 35C15, 65R20.Received May 2004. Accepted September 2004. Communicated by Anders Szepessy.Johan Helsing: This work was supported by the Swedish Science Research Council under contract 621-2001-2799.     

非线性椭圆型偏微分方程弱解的存在性

在W1,p(x)空间框架下研究了具有p(x)增长条件的椭圆型偏微分方程:-d iva(x,u,D u) g(x,u,u)=f,得到了在W10,p(x)空间中弱解的存在性,推广了Boccardo等关于在Sobo lev空间中弱解的相应结论.     

高阶拟线性椭圆型方程奇摄动问题

本文利用微分不等式和多重尺度，研究了一个高阶椭圆型偏微分方程摄动边值问题，并得到了一致有效的渐近展开式。     

一类拟线性偏微分方程组的Laplace空间解的形式相似性

本作研究了一类拟线性偏微分方程组在不同的外边界条件(无穷大外边界，封闭外边界，定值外边界)和随机时间变化的内边界条件下的初值问题在Laplace空间的解的形式相似性，它能很好地帮助我们认识模型遵从的内在规律及设计相应的应用软件．     

如何不用复数讲解常系数线性微分方程

在高等数学课程中,复指数函数及其导数知识的严格讲解,通常要比微分方程知识的讲解晚很多.这使得微分方程的教学在逻辑上有些不足.用复值函数解的复系数线性组合推导出实值函数解,在教学实践中,学生经常感到迷惑.不以复数的任何知识作为前提,给出了常系数微分方程的一种自然的讲解方法.     

SHARP UPPER BOUNDS FOR THE DEGREE OF REGULARITY OF THE SOLUTIONS TO AN ELLIPTIC EQUATION

ABSTRACT

We show that regularity of solutions to the well known Serrin equation is governed by that of particular ones, that we call principal solutions.     

The strengthened C.B.S. inequality constant for second order elliptic partial differential operator and for hierarchical bilinear finite element functions

We estimate the constant in the strengthened Cauchy-Bunyakowski-Schwarz inequality for hierarchical bilinear finite element spaces and elliptic partial differential equations with coefficients corresponding to anisotropy (orthotropy). It is shown that there is a nontrivial universal estimate, which does not depend on anisotropy. Moreover, this estimate is sharp and the same as for hierarchical linear finite element spaces.This research was supported by the Grant Agency of Czech Republic under the contract No. 201/02/0595.     

共振情形下次线性椭圆偏微分方程的解

研究了共振下的微分方程Δｕ＋λ_１ｕ＋ｇ（ｘ,ｕ）＝０,ｘ∈?Ω;ｕ｜_?Ω＝０．在ｇ（ｘ,ｕ）关于ｕ次线性的情形,证明了解的存在性,从而部分地回答了Ｆｉｇｕｅｉｒｅｄｏ ａｎｄ Ｍａｓｓａｂｉ的一个问题．     

On the robustness of the BPX-preconditioner with respect to jumps in the coefficients

We determine the worst case behavior of the standard BPX-preconditioner for elliptic problems with arbitrary coefficient jumps along the boundaries of the coarsest partition. The counterexamples are also useful for other problems.

     

Concentrating solutions of some singularly perturbed elliptic equations

We study singularly perturbed elliptic equations arising from models in physics or biology, and investigate the asymptotic behavior of some special solutions. We also discuss some connections with problems arising in differential geometry.      

FINITE ELEMENT AND DISCONTINUOUS GALERKIN METHOD FOR STOCHASTIC HELMHOLTZ EQUATION IN TWO- AND THREE-DIMENSIONS

In this paper, we consider the finite element method and discontinuous Galerkin method for the stochastic Helmholtz equation in R^d （d = 2, 3）. Convergence analysis and error estimates are presented for the numerical solutions. The effects of the noises on the accuracy of the approximations are illustrated. Numerical experiments are carried out to verify our theoretical results.