最佳逼近与Fourier系数的等价关系

探讨最佳逼近E_n(f)与函数的Fourier系数\!$\hat{f}(n)\in {\bf C},n=0,\pm 1,\pm 2,\ldots$, 在\!$\{\hat{f}(n)\}_{n=0}^{\infty }\linebreak\in $MVBVS^*和$\{\hat{f}(n)+f\left( -n\right) \}_{n=0}^{\infty }\in$ MVBVS^*条件下的等价关系问题, 此地MVBVS^*为所称的强均值有界变差(strong mean value bounded variation)数列的集合.     

和的乘积的重对数律

设{X,X_n,n≥1}是独立的或φ -混合的或 ρ -混合的正的平稳随机变量序列，或$\{X,X_n,n≥1}$是正的随机变量序列使得{X_n-EX,n≥1\} 是平稳遍历的鞅差序列，记S_n=\sum\limitsⁿ_{j=1}X_j, n≥1 . 该文在条件EX=μ> 0 及0 Var(X)<∞下，证明了部分和的乘积$\prod\limits^n_{j=1}S_j/n!\mu^n$在合适的正则化因子下的某种重对数律.     

对于轮和完全图的 Ramsey 数的渐近上界

该文给出:对于偶数m≥4当n→ ∞时 r(W_m,K_n)≤l(1+o(1))C₁(m) (n/logn ) ^(2m-2)/(m-2)对于奇数m≥5当n→∞时r(W_m,K_n)≤(1+o(1))C₂(m) (n^2m/_m+1/^{_{log n)}(m+1)/(m-1)} .特别地,C₂(5)=12. 以及 c(ⁿ/_logn)^5/2≤r(K₄,K_n)≤ (1+o(1)) ^n3_/(logn)².此外,该文还讨论了轮和完全图的 Ramsey 数的一些推广.     

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.     

具有缺项系数的几类解析函数族的性质

S*表示所有在单位圆盘 D 内解析且满足条件 f(0)=f′ (0)-1=0的星形函数族, K 表示所有在 D内解析且满足条件 f(0)=f′ (0)-1=0 的凸函数族, P 表示所有在 D 内解析且满足条件p(0)=1, Rep(z)>0 的函数族. 设P_n={p(z): p(z)=1+a_nzⁿ+a_n+1zⁿ⁺¹+…∈ P}, S*_n={f (z): f(z)=z+a_nzⁿ+a_n+1zⁿ⁺¹+…∈ S*}, K_n={f (z): f (z)=z+a_nzⁿ+a_n+1zⁿ⁺¹+…∈ K}. L_Sn*={g(z)=ln f(z)/z, f ∈ S_n*}, 其中对数函数取使得ln1=0的那个单值解析分支. 该文研究了函数族S_n^*, K_n和L_Sn*的性质, 找出了解析函数族L_Sn*的极值点与支撑点,并对S*_n与K_n的极值点和支撑点作了一些探讨.     

四元数射影空间中的全实极小2维球面

设HPⁿ是具有常四元数截面曲率4的四元数射影空间, 则局部上存在HPⁿ的3个复结构{I,J,K},满足IJ=-JI=K, JK=-KJ=I, KI=-IK=J. 曲面MÌHPⁿ称为全实的, 如果对每一点p∈M,切平面T_pM垂直于I(T_pM), J(T_pM)及K(T_pM). 已知任意曲面MÌ RPⁿ Ì HPⁿ 是全实的, 这里 RPⁿ Ì HPⁿ 是实射影空间在HPⁿ 中由包含映射R Ì H诱导的标准嵌入映射, 还知道在HPⁿ中存在不属于这种情形的全实曲面. 证明了HPⁿ中任意全实极小2维球面等距于RP^2m Ì CPⁿ Ì HPⁿ 中一个满的极小2维球面, 这里2m ≤ n. 作为推论, 证明了RP^2m (m≥1) 中的Veronese曲面是四元数射影空间中仅有的具常曲率的全实极小2维球面.     

四阶椭圆方程基态解的集中性态

该文分析了四阶椭圆方程△^２u=|x|^au^p-1,x∈Ω; u=\Delta u=0 , x ∈аΩ, (Ω表示Rⁿ中以原点为中心的球)基态解的集中性态,并证明了当p趋近于 2^*=\frac{2n}{n-4} (n>4)时基态解u_p集中在Ω的边界附近.     

同分布 ρ 混合序列的最大值不等式及其应用

设X_n,n≥1是同分布的ρ混合序列, 记S_n=∑ⁿ_{i=1 Xi}. 该文讨论了$\max\limits_{1\leq i\leq n}\frac{|S_i|}{i}$ $(n\geq1)$的分布函数的上界. 作为应用,获得了随机变量$\sup\limits_{n\geq1}\frac{|S_n|}{n}$的1阶矩及$p(>1)$阶矩分别存在有限的充分必要条件,这是一个与独立同分布场合相一致的结果.     

交比和Poincare度量在平面拟共形映射下的偏差

研究(1)若f是 R²到 R²上的k -拟共形映射, 则对任意x₁,x₂,x₃,x_4∈R²有16^{\frac1k-1}(|(x₁,x_2, x₃,x₄)|+1)^{\frac1k}&;\leq&; \left|\left(f(x_1), f(x_2),f(x_3),f(x_4)\right)\right|+1\\&; \leq&; 16^{k-1}\left(|(x_1,x_2,x_3,x_4)|+1\right)^{k}; \end{eqnarray*}(2)若f是R²到R²上的k -拟共形映射, D是R²中的任一真子域,则对任意x₁,x₂∈D有\begin{eqnarray*}\frac1k\lambda_D(x_1,x_2)+4(\frac1k-1)\log2&;\leq&; \lambda_{f(D)} (f(x_1),f(x_2))\\&;\leq &;k\lambda_D(x_1,x_2)+4(k-1)\log2.\end{eqnarray*}了交比和Poincar\'e度量在平面拟共形映射下的偏差估计, 得到了如下两个结果.     

Hilbert空间上线性算子广义逆A(2)T,S的存在性及其表示式

设H₁和H₂是两个Hilbert空间, B(H₁,H₂)表示从H₁到H₂的所有有界线性算子的集合, T和S分别是H₁和H₂的两个闭子空间. 如果存在线性算子X ∈ B(H₂,H₁)满足XAX=X, R(X)=T, N(X)=S,则称X为线性算子$A$的具有指定像空间T和零空间S的外逆,记为A⁽²⁾_T,S. 该文进一步研究了线性算子广义逆A⁽²⁾_T,S存在的若干等价条件及其性质,建立了算子广义逆A⁽²⁾_T,S的表示形式.     

An existence theorem for the complementarity problem

LetC be a pointed, solid, closed and convex cone in then-dimensional Euclidean spaceE ⁿ ,C* its polar cone,M:C→E ⁿ a map, andq a vector inE ⁿ . The complementarity problem (q|M) overC is that of finding a solution to the system $$(q|M) x \varepsilon C, M(x) + q \varepsilon C{^*} , \left\langle {x, M(x) + q} \right\rangle = 0.$$ It is shown that, ifM is continuous and positively homogeneous of some degree onC, and if (q|M) has a unique solution (namely,x=0) forq=0 and for someq=q ₀ ∈ intC*, then it has a solution for allq ∈E ⁿ .     

一类反对称正交反对称矩阵逆特征值问题

设P为一给定的对称正交矩阵,记AARnP={A∈Rn×n‖AT=-A,(PA)T=-PA}.讨论了下列问题:问题给定X∈Cn×m,Λ=diag(λ1,λ2,…,λm).求A∈AARPn使AX=XΛ.问题设A~∈Rn×n,求A*∈SE使‖A~-A*‖=infA∈SE‖A~-A‖,其中SE为问题的解集合,‖.‖表示Frobenius范数.研究了AARPn中元素的通式,给出了问题解的一般表达式,证明了问题存在唯一逼近解A*,且得到了此解的具体表达式.     

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.     

On the Discontinuous Infinite-Dimensional Generalized Quasivariational Inequality Problem

In this paper, we deal with the following generalized quasivariational inequality problem: given a real normed space E with topological dual E* and two multifunctions G: X→2 ^X and F: X→2 ^E*, find $\left( {\hat x,\hat \phi } \right)$ ∈X × E* such that $\hat x \in G\left( {\hat x} \right),{\text{ }}\hat \phi \in F\left( {\hat x} \right),{\text{ }}\left\langle {\hat \phi ,\hat x - y} \right\rangle \leqslant 0,{\text{for all }}y \in G\left( {\hat x} \right).$ We extend to such infinite-dimensional setting some existence results which have been obtained recently for the special case where E is finite dimensional. In particular, our assumptions do not imply any kind of continuity for the multifunction F.     

The Solvability Conditions for the Inverse Problem of Matrices Positive Semidefinite on a Subspace

Inverseproblemsforrealsymmetricmatricesandsymmetricnonnegativedefinitematriceshavebeenstudiedin[1],[2].Theconditionsfortheexistenceofasolutiontheexpressionofthegeneralsolutionandoptimalapproximatesolutionhavebeengiven.Thispaperstudiestheinverseproblemofonekindofmatricesbetweentheabovetwokindsofmatrices-matricespositivesemidefiniteonasubspace.Theconditionsfortheexistenceofasolution,theexpressionofthegeneralsolutionandtheoptimalapproximatesolutionaregiven'Inthispaper9Rnxmdenotesthesetofallrealn…     

Boundary distortion and variation of the module under an extension of a doubly connected domain

Theorem 2

Let f(z) ∈ $\mathcal{F}(\rho ,r)$ , f(z) ≠ e^iα f(z;pr), α ∈ ?, and let ?(t) be a strictly convex monotone function of t>0. Then $$\int\limits_0^{2\pi } {\Phi (|f'(e^{i\theta } )|)d\theta< } \int\limits_0^{2\pi } {\Phi (|f'(e^{i\theta } ;\rho ,r)|)d\theta } $$ . The proof of this theorem is based on the Golusin-Komatu equation. If E is a continuum in the disk U_R={z:|z|<R}, then M (R, E) denotes the conformal module of the doubly connected component of U_R/E; let $\varepsilon (m) = \{ E:\overline U _r \subset E \subset U_1 , M(1,E) = M^{ - 1} \} $ .

Problem 3

Find the maximum of M(R, E), R>1, and the minimum of cap E over all E in ε(m). This problem was posed by V. V. Kozevnikov in a lecture to the Seminar on Geometric Function Theory at the Kuban University in 1980, and by D. Gaier (see [2]). The solution of this problem is given by the following theorem.

Theorem 3

Let $E^* = \underline U _m \cup [m,s]$ . If R>1; E, E^* ∈ ε(m) and E ≠ e^iα E*, α ∈ ?, then M(R, E)<M(R, E^*), capE^*<capE. A similar statement is also proved for continua lying in the half-plane. Bibliography: 7 titles.     

L^p -uniqueness for Dirichlet operators with singular potentials

We study the problem of strong uniqueness in L^p for the Dirichlet operator perturbed by a singular complex-valued potential. First we construct the generator -H_p of a C₀-semigroup in L^p, with H_p extending the restriction of the perturbed Dirichlet operator to the set of smooth functions. The corresponding sesquilinear form in L² is not assumed to be sectorial. Then we reveal sufficient conditions on the logarithmic derivative # of the measure rdx \rho dx and the potential q which ensure that -H_p is the only extension of D+b·?-q \upharpoonright_C0^￥ \Delta +\beta \cdot \nabla -q \upharpoonright_{C_0^{\infty}} which generates a C₀-semigroup on L^p. The method of a priori estimates of solutions to corresponding differential equations is employed.     

On approximation theorems for controllability of non-linear parabolic problems

^** Email: anil{at}math.iitb.ac.in^*** Email: mcj{at}math.iitb.ac.in^**** Email: akp{at}math.iitb.ac.in In this paper, we consider the following control system governedby the non-linear parabolic differential equation of the form: [graphic: see PDF] where A is a linear operator with dense domain and f(t, y)is a non-linear function. We have proved that under Lipschitzcontinuity assumption on the non-linear function f(t, y), theset of admissible controls is non-empty. The optimal pair (u^*,y^*) is then obtained as the limit of the optimal pair sequence{(u_n^*, y_n^*)}, where u_n^* is a minimizer of the unconstrainedproblem involving a penalty function arising from the controllabilityconstraint and y_n^* is the solution of the parabolic non-linearsystem defined above. Subsequently, we give approximation theoremswhich guarantee the convergence of the numerical schemes tooptimal pair sequence. We also present numerical experimentwhich shows the applicability of our result.