Birkhoff遍历定理的推广

设(X,F,P)是一个概率空间,T:X→X 为保测变换,Bikhoff 遍历是定理指出:对任意 f∈L′(X,F,P),都存在 f~*∈L′(X,F,P)使得(?)并且 f~*(?)T=f~*α.e,α.e,(?)f*(x)dP=(?)f*(x)dP.J.P.con-(?)并且(?)ze 与 A.Bellow 分别在[1]、[2]中讨论了对任意一串严格增的正整数 κ=(k_n)m>0,部分和 T~N,kf(x)=1/N sum from n≤N f(T?)当 N→∞时的收敛性。本文中,我们要从另外的角度来讨     

评《关于膨胀算子不动点定理的注记》一文

在文献[1]中,于挺同志证明了下述定理: 定理1设(X,d)是紧度量空间,T是X→X的连续映射,如果存在h>0,对任意x,y∈X,有 d(TX,TY)≥hd(x,y) (1)则T在X中有唯一不动点x_*,且对任意x_0∈X,x_n=TX_(n-1)(n=1,2,…),有=x_*。 我们可以证明: 当X至少有两个点时,满足定理1条件的映射不存在。 证明 用反证法,设存在映射T满足定理1的条件。由X至少有两个不同的点及(1)式易知T≠Ⅰ(Ⅰ是X→X的恒等映射)。     

关于结合环上的微商

设R为结合环,d为其上的可加变换,且对任意x,y∈R都有 d(xy)=d(x)y xd(y)则说d是R的一个微商。 Herstein在文[1]中证明了一个有名的定理,设R是特征数不为2的质环,d是R的一个微商,且对任意x,y∈R有 d(x)d(y)=d(y)d(x) 则d为零变换或者R为可换环。 本文用相当明了的方法给出微商变换的一个重要性质,它把上述Herstein定理在两个方向上做了推广。     

一个新的压缩型映象的不动点定理

设X是完备的度量空间,T:X→X是连续映象,若存在X×X上对称实函数φ(x,y).使T满足φ(Tx,Ty)≤aφ(x,y), x,y∈X及d(Tx,Ty)≤cd(x,y)+φ(x,y), x,y∈X,其中d是X上的度量,两个常数a,c满足0≤a<1,0≤c<1.本文证明了映象T有唯一的不动点x_*,且 x∈X,有T_x~n→x_*(n→∞).在φ(x,x)=0,φ是一元连续的条件下,证明了在X上一定存在一个拓扑等价的度量d~*使T关于d~*是X上的Banach压缩映象.     

共振下一类常微分方程组周期解的唯一存在性

设 X,Y 是 Banach 空间,其中范数不加区分地都记作‖·‖。首先我们给出 Hada-mard 大范围隐函数定理新的证明,这个证明比较初等,它并不涉及覆盖空间和提升等概念。定理1 (Hadamard)。设 T∶X→Y 是连续 Fréchet 可微映射,假定对一切 x∈X,T 的 Fréchet 微商 T′(x)都是 X 到 Y 上的线性同胚。令ζ(R)(?)(?)(1/‖[T′(x)]~(-1)‖),如果 integral from 0 to ∞ ζ(R)dR= ∞,那么 T 是 X 到 Y 上的同胚。     

全变换半群的极大半传递幺半群(英文)

对任一个非空集X,X上的全变换半群T(X)的一个子幺半群M被称为半传递,如果M为非传递,且对每个序对(x,y)∈X×X,存在∈M使x=y或y=x.本文刻画了全变换半群T(X)的所有极大半传递子幺半群;对T(X)的每个极大半传递子幺半群M,相关秩r(T(X),M)被证明为1.对有限集X,给出T(X)的极大半传递子幺半群的个数,且T(X)的最大基数的半传递子幺半群被刻画.     

局部化单调原理及应用

以下我们总假定(X,d)表度量空间,简记为X,T为X的自映象,B:X?R_+~0=[0,+∞)。我们称X满足广义TCS收敛条件,若存在一点x_0∈X使得{B(T~nx_0)}收敛,蕴含{T~nx_0}有一个收敛子列。称σ(x,T)={x,T_x,T~2x,…,T~nx,…}为x的T轨道。称函数B(x)在p∈X点轨道连续,若{x_n}?σ(x,T),x_n→p,有B(x_n)?B(p)。若B(x)在X内每一点轨道连续,称B(x)在X上轨道连续。我们有如下结果。     

Banach空间上有界可逆线性变换逆变换的结构

Fillmore在[1]中得到一个定理:设A,T是Banach空间X上的线性变换,A有界,若Lat(A) Lat(T)且AT=TA,则T是A的多项式.在本文里,以此作为引理,讨论了Banach空间上可逆线性变换A在什么情况下,A-1可表示为A的多项式.本文最主要的结论是定理3.4:设X是Banach空间,A是X上的有界线性变换,且可逆,则A-1是A的多项式当且仅当A-1是A的局部多项式.     

关于(1)-(25)类压缩映象的等价性问题及某些不动点定理

设(X,d)是一完备度量空间,T 是映 X 到 X 的连续映象,各种类型的压缩映象类中,最基础的是(1)—(25)类的压缩映象,其他类型的压缩映象都是由它们引伸和发展起来的.弄清(1)—(25)类压缩映象间的关系是很有意义的,许多压缩映象尽管形式上各不相同,但在拓扑等价度量意义下是 Banach 型的压缩映象。Rhoades 张石生……等人对这一问题作了系统的研究.本文进一步的得出了 T 在 X 上凝聚,且(?)x∈X,轨道O(x,T)有界,(1)—(25)类压缩映象在拓扑等价度量意义下是相互等价的.另外Rhoades 在文提出了若 T∈(25),在 X 上连续,对某个 x_0∈X,{T~n x_0}有一个聚点,T 存在不动点吗?若答案是否定的,那么对 X 或 T 应加什么条件才能保证不动点的存在?     

函数|f(x)|和f(|x|)的周期性

本文讨论连续的周期函数f(x)分别与函数|f(x)|、f(|x|)之间的周期性和最小正周期的关系,其中f(x)(?)c(常数)。 定理1.若f(x)为非常数的连续周期函数,则|f(x)|也是连续的周期函数。 证明:显然f(x)与|f(x)|有相同的定义域X.f(x)(?)c,则连续的周期函数f(x)必有最小正周期T(证明可见参考资料[1])。     

On quantitative versions of theorems due to F.E. Browder and R. Wittmann

This paper is another case study in the program of logically analyzing proofs to extract new (typically effective) information (‘proof mining’). We extract explicit uniform rates of metastability (in the sense of T. Tao) from two ineffective proofs of a classical theorem of F.E. Browder on the convergence of approximants to fixed points of nonexpansive mappings as well as from a proof of a theorem of R. Wittmann which can be viewed as a nonlinear extension of the mean ergodic theorem. The first rate is extracted from Browder's original proof that is based on an application of weak sequential compactness (in addition to a projection argument). Wittmann's proof follows a similar line of reasoning and we adapt our analysis of Browder's proof to get a quantitative version of Wittmann's theorem as well. In both cases one also obtains totally elementary proofs (even for the strengthened quantitative forms) of these theorems that neither use weak compactness nor the existence of projections anymore. In this way, the present article also discusses general features of extracting effective information from proofs based on weak compactness. We then extract another rate of metastability (of similar nature) from an alternative proof of Browder's theorem essentially due to Halpern that already avoids any use of weak compactness. The paper is concluded by general remarks concerning the logical analysis of proofs based on weak compactness as well as a quantitative form of the so-called demiclosedness principle. In a subsequent paper these results will be utilized in a quantitative analysis of Baillon's nonlinear ergodic theorem.     

真拟弱几乎周期点和拟正则点

T为紧致度量空间X上的连续映射,M（X）为X上所有Borel概率测度.设x∈X,记Mx（T）为概率测度序列{1n∑n 1i=0δTi（x）}在M（X）中的极限点的集合,其中δx表示支撑集是{x}的点测度.记W（T）和QW（T）分别为T的弱几乎周期点和拟弱几乎周期点集.本文证明,如果（X,T）非平凡且满足specifcation性质,则存在x,y∈QW（T）／W（T）（称为真拟弱几乎周期点）,分别满足μ∈Mx（T）,x∈Supp（μ）和ν∈My（T）,y∈/Supp（ν）,回答了周作领等提出的公开问题.Mx（T）在弱拓扑中是紧致连通集,所以,要么是单点集,要么是不可数集.如果x∈QW（T）／W（T）,则Mx（T）是不可数集.一个自然的问题是,怎么刻画M x（T）是单点集的点x（这时x称为拟正则点）.本文给出M x（T）是单点集的充要条件.     

A simple proof of some ergodic theorems

Some ideas of T. Kamae’s proof using nonstandard analysis are employed to give a simple proof of Birkhoff’s theorem in a classical setting as well as Kingman’s subadditive ergodic theorem.     

Uniformity seminorms on ℓ<Superscript>∞</Superscript> and applications

A key tool in recent advances in understanding arithmetic progressions and other patterns in subsets of the integers is certain norms or seminorms. One example is the norms on ℤ/Nℤ introduced by Gowers in his proof of Szemerédi’s Theorem, used to detect uniformity of subsets of the integers. Another example is the seminorms on bounded functions in a measure preserving system (associated to the averages in Furstenberg’s proof of Szemerédi’s Theorem) defined by the authors. For each integer k ≥ 1, we define seminorms on ℓ^∞(ℤ) analogous to these norms and seminorms. We study the correlation of these norms with certain algebraically defined sequences, which arise from evaluating a continuous function on the homogeneous space of a nilpotent Lie group on a orbit (the nilsequences). Using these seminorms, we define a dual norm that acts as an upper bound for the correlation of a bounded sequence with a nilsequence. We also prove an inverse theorem for the seminorms, showing how a bounded sequence correlates with a nilsequence. As applications, we derive several ergodic theoretic results, including a nilsequence version of the Wiener-Wintner ergodic theorem, a nil version of a corollary to the spectral theorem, and a weighted multiple ergodic convergence theorem.     

反正切相加定理的一种新证法

利用微分方程给出了反正切相加定理的一种新证法,该方法可直接确定反正切相加定理中函数ε(x,y)的连续域以及函数在域内的取值.     

The central limit theorem and chaos

Let X be a compact metric space studies some relationships between stochastic and f ： X→ X be a continuous map. This paper and topological properties of dynamical systems. It is shown that if f satisfies the central limit theorem, then f is topologically ergodic and / is sensitively dependent on initial conditions if and only if / is neither minimal nor equicontinuous.     

The the uniform mean-square ergodic theorem for wide sense stationary processes

It is shown that the uniform mean-square ergodic theorem holds for the family of wide sense stationary sequences, as soon as the random process with orthogonal increments, which corresponds to the orthogonal stochastic measure generated by means of the spectral representation theorem, is of bounded variation and uniformly continuous at zero in a mean-square sense. The converse statement is also shown to be valid, whenever the process is sufficiently rich. The method of proof relies upon the spectral representation theorem, integration by parts formula, and estimation of the asymptotic behaviour of total variation of the underlying trigonometric functions. The result extends and generalizes to provide the uniform mean-square ergodic theorem for families of wide sense stationary processes     

一个微分中值命题条件的弱化

讨论一个微分中值命题条件的弱化,将条件“f′（x）g′（x）〉0”弱化为“f（a）≠f（b）”,利用介值定理和柯西中值定理给出证明,以扩大命题的适用范围,并举出实例予以说明．     

A rapidly-converging lower bound for the joint spectral radius via multiplicative ergodic theory

We use ergodic theory to prove a quantitative version of a theorem of M.A. Berger and Y. Wang, which relates the joint spectral radius of a set of matrices to the spectral radii of finite products of those matrices. The proof rests on a structure theorem for continuous matrix cocycles over minimal homeomorphisms having the property that all forward products are uniformly bounded.     

奇异二阶泛函微分方程积分边值问题的正解

通过锥拉伸与压缩定理讨论了如下二阶泛函微分方程积分边值问题正解的存在性,其中m：（0,T）→[0,＋∞）连续,并且0〈∫_0~Tm（s）ds〈1;h：（0,T）→[0,＋∞）连续,可在t=0和t=T处奇异且0〈∫_0~Th（s）ds〈＋∞.