一种Cauchy型主值积分的求积公式的一致收敛性

该文首先给出Cauchy型主值积分φ(wf,x)的一种求积公式φ_m^*(wf,x),然后证明序列$φ_m^*(wf,x)}_m=2^∞在整个闭区间[-1,1]上是一致收敛到Cauchy型主值积分φ(wf,x)的,同时给出它的误差界.     

定义在迭代函数系统吸引子上的动力系统的平衡态

在该文中, 令E表示一个迭代函数系统(X,T₁,…, T_m). 的吸引子. 定义连续自映射 f : E→E为f(x)=T^-1_j(x), x∈ T_j(E), j=1, …, m . 给定Given ψ ∈C_R(E), 令 K_ψ(δ, n = sup{∣∑^n-1_k=0[ψ(f ^kx)-ψ(f ^ky)]|:y ∈ B_x (δ, n)}, 这里B_x(δ, n) 表示Bowen球. 取一个扩张常数 ε, 记K_ψ=sup_n K_ψ(ε, n) , 定义ν(E)={ψ : K_ψ < ∞}. 对f : E → E, 作为Ruelle的一个定理^{[3, 定理2.1]}的一个应用, 我们证明每个ψ ∈ν(E)具有惟一的平衡态. 此结果推广了文献[12]中的主要结果.     

二阶超线性差分方程周期解与次调和解的存在性

应用临界点理论, 为研究差分方程周期解与次调和解的存在性和多重性提供了一种新方法. 对二阶差分方程 D²x_n-1+f (n, x_n)=0, 当f(t, z)在0点及无穷远点为超线性增长时, 上述问题得到某些新结果.     

极大单调算子的一个新的近似邻近点算法

研究集值映射方程0 T (z)的求解问题, 其中T是极大单调算子.对于给定的x^k及β _k>0, 大部分已有的近似邻近点算法取x^k+1= 满足 x^k +e^k +β_kT(x^k ), ||e^k||≤h_k||x_k- x^k ||, 其中{h^k}为非负可加数列. 新方法中不取 x^k+1 = x^k , 而将新的迭代点取为 x^k+1 = P_Ω [x^k-e^k], 其中Ω 是T的定义域,P_Ω (&#8729;) 表示Ω上的投影算子. 在supk>0h^k < 1这样宽松的条件下给出了收敛性证明.     

带强迫项的二阶非线性椭圆方程的区域振动准则

对二阶非线性椭圆型方程∑ _i,j=1ⁿ D_i[A_ij(x)D_jy]+∑_i=1ⁿ b_i(x)D_iy+q(x)f(y)=e(x)建立了若干新的振动准则, 所得结果仅依赖于方程在外区域Ω С Rⁿ的一个子区域序列的信息而有别于已知的大多数结论.     

一类修正的Navier-Stokes方程的长时间性态

该文主要讨论,Rⁿ上一类修正的 Navier-Stokes 方程弱解的长时间性态, 通过进一步改进Fourier分解方法, 得到了当初速度u_0∈ L² ∩L¹时其弱解在L² 范数下的最优衰减率为 (1+t)^n/4 同时该文也给出了修正的Navier-Stokes 方程与经典Navier-Stokes 方程的误差估计.     

一类带权函数的拟线性椭圆方程

该文利用变分方法讨论了方程 -△_p u=λa(x)(u⁺)^p-1-μa(x)(u^-)^p-1+f(x, u), u∈W₀^1,p(\Omega)在(λ, μ)\not\in ∑_p和(λ, μ) ∈ ∑_p 两种情况下的可解性, 其中\Omega是 R^N(N≥3)中的有界光滑区域, ∑_p为方程 -△_p u=α a(x)(u⁺)^p-1-βa(x)(u^-)^p-1, u∈ W₀^1,p(\Omega)的Fucik谱, 权重函数a(x)∈ L^r(\Omega) (r≥ N/p)$且a(x)>0 a.e.于\Omega, f满足一定的条件.     

拟齐性偏微分方程的多项式解

设p是Rⁿ上具C^∞系数的线性偏微分算子,关于拟相似变换δ_τ(x)=(τ>0)是m次拟齐性的,m>0,如果a₁,a₂,…,a_n全为正有理数或m∈M={α·a,α∈Iⁿ₊},则方程p[u]=0的多项式解空间必为无穷维的.     

偶数阶Sturm-Liouville边值问题的多个正解

该文讨论了偶数阶边值问题 (-1)^m y^(2m)₌f(t,y), 0≤t≤1,a_i+1y⁽²ⁱ⁾ (0)-β_i+1y ⁽²ⁱ⁺¹⁾ (0)=0, γ_i+1y⁽²ⁱ⁾ (1)+δ_i+1y⁽²ⁱ⁺¹⁾ (1)=0,0≤i ≤m-1正解的存在性.借助于Leggett-Williams 不动点定理,建立了该问题存在三个及任意奇数个正解的充分条件.     

关于单位圆内解析系数的线性微分方程的复振荡理论

该文研究了线性微分方程L(f)=f^(k)+A_k-1(z)f^(k-1)+ ^… +A₀(z)f=F(z) (k∈ N)的复振荡理论, 其中系数A_j(z) (j=0, ^… , k-1)和F(z)是单位圆△={z:|z|<1}内的解析函数. 作者得到了几个关于微分方程解的超级, 零点的超收敛指数以及不动点的精确估计的定理.     

An additive Schwarz method for the h-p version of the boundary element method for hypersingular integral equations in R3

We study a preconditioner for the h-p version of the boundaryelement method for hypersingular integral equations in threedimensions. The preconditioner is based on a three-level decompositionof the underlying ansatz space, the levels being piecewise bilinearfunctions on a coarse grid, piecewise bilinear functions ona fine grid, and piecewise polynomials of high degree on thefine grid. We prove that the condition number of the preconditionedlinear system is bounded by max_j (1 + log H_jp_j/h_j)² where H_jis the diameter of an element _j of the coarse grid, h_j is thesize of the elements of the fine grid on _j, and p_j is the maximumof the polynomial degrees used in _j. Numerical results supportingour theory are reported. Received 9 March 1999. Accepted 19 July 1999.     

On the numerical quadrature of highly-oscillating integrals I: Fourier transforms

Highly-oscillatory integrals are allegedly difficult to calculate.The main assertion of this paper is that that impression isincorrect. As long as appropriate quadrature methods are used,their accuracy increases when oscillation becomes faster andsuitable choice of quadrature points renders this welcome phenomenonmore pronounced. We focus our analysis on Filon-type quadratureand analyse its behaviour in a range of frequency regimes forintegrals of the form ₀^h f(x)e^{i x} w(x)d x, where h>0 issmall and | | large. Our analysis is applied to modified Magnus methods for highly-oscillatoryordinary differential equations. Received 6 June 2003. Revised 14 October 2003.     

Extrapolation algorithms for solving nonlinear boundary integral equations by mechanical quadrature methods

We study the numerical solution procedure for two-dimensional Laplace’s equation subjecting to non-linear boundary conditions. Based on the potential theory, the problem can be converted into a nonlinear boundary integral equations. Mechanical quadrature methods are presented for solving the equations, which possess high accuracy order O(h ³) and low computing complexities. Moreover, the algorithms of the mechanical quadrature methods are simple without any integration computation. Harnessing the asymptotical compact theory and Stepleman theorem, an asymptotic expansion of the errors with odd powers is shown. Based on the asymptotic expansion, the h ³ −Richardson extrapolation algorithms are used and the accuracy order is improved to O(h ⁵). The efficiency of the algorithms is illustrated by numerical examples.     

On the Local and Superlinear Convergence of Quasi-Newton Methods

This paper presents a local convergence analysis for severalwell-known quasi-Newton methods when used, without line searches,in an iteration of the form to solve for x^* such that Fx^* = 0. The basic idea behind theproofs is that under certain reasonable conditions on x_o, Fand x_o, the errors in the sequence of approximations {H_k} toF'(x^*)^–1 can be shown to be of bounded deterioration inthat these errors, while not ensured to decrease, can increaseonly in a controlled way. Despite the fact that H_k is not shownto approach F'(x^*)^–1, the methods considered, includingthose based on the single-rank Broyden and double-rank Davidon-Fletcher-Powellformulae, generate locally Q-superlinearly convergent sequences{x_k}.     

A Note on a Maximal Function Over Arbitrary Sets of Directions

Let M_S be the universal maximal operator over unit vectors ofarbitrary directions. This operator is not bounded in L²(R²).We consider a sequence of operators over sets of finite equidistributeddirections converging to M_S. We provide a new proof of N. Katz'sbound for such operators. As a corollary, we deduce that M_Sis bounded from some subsets of L² to L². These subsets arecomposed of positive functions whose Fourier transforms havea logarithmic decay or which are supported on a disc. 1991 MathematicsSubject Classification 42B25.     

Mechanical quadrature methods and their extrapolation for solving first kind Abel integral equations

This paper presents high accuracy mechanical quadrature methods for solving first kind Abel integral equations. To avoid the ill-posedness of problem, the first kind Abel integral equation is transformed to the second kind Volterra integral equation with a continuous kernel and a smooth right-hand side term expressed by weakly singular integrals. By using periodization method and modified trapezoidal integration rule, not only high accuracy approximation of the kernel and the right-hand side term can be easily computed, but also two quadrature algorithms for solving first kind Abel integral equations are proposed, which have the high accuracy O(h²)$\mathrm{O}(h^2)$ and asymptotic expansion of the errors. Then by means of Richardson extrapolation, an approximation with higher accuracy order O(h³)$\mathrm{O}(h^3)$ is obtained. Moreover, an a posteriori error estimate for the algorithms is derived. Some numerical results show the efficiency of our methods.