序列的一致分布及其与泛函分析的相互作用
Uniform Distribution of Sequences and its interplay with Functional Analysis
AI总结:
本文将序列一致分布理论应用于泛函分析,证明了Banach空间及其对偶空间中关于闭凸包子集的Cesàro可和性与弱*收敛性定理,并借此推广了一致分布理论中关于有界变差函数的经典定理。
摘要:
在本文中,我们将序列一致分布理论的思想应用于泛函分析,并从所得结果中汲取灵感,进而研究一致分布本身的概念与结果。设 $E$ 为一个 Banach 空间。我们证明:\\(a) 若 $F$ 是 $E$ 的有界子集且 $x \in \overline{\co}(F)$(即 $F$ 的闭凸包),则存在一个序列 $(x_n) \subseteq F$ Cesàro 可和至 $x$。\\(b) 若 $E$ 是可分的,$F \subseteq E^*$ 有界且 $f \in \overline{\co}^{w^*}(F)$,则存在序列 $(f_n) \subseteq F$,其算术平均序列 $\frac{f_1+\dots+f_N}{N}$($N \ge 1$)弱$^*$ 收敛于 $f$。借助 Krein-Milman 定理,(a) 和 (b) 对于 $E$ 中满足 $Ω=\overline{\co}(\ex Ω)$ 的闭、凸且有界子集 $Ω$,以及 $E^*$ 中的弱$^*$ 紧且凸的子集,具有有趣的推论。特别令人感兴趣的是 $Ω=B_{C(K)^*}$ 的情况,其中 $K$ 是紧度量空间。通过进一步扩展上述思想与结果,我们能够推广一致分布的一个经典定理,该定理原本对满足 $φ(0)=0$ 和 $φ(1)=1$ 的递增函数 $φ:I=[0,1] \rightarrow \mathbb{R}$ 成立,推广至 $I$ 上满足 $φ(0)=0$ 且全变差 $V_0^1 φ=1$ 的有界变差函数 $φ$。
英文摘要:
In this paper we apply ideas from the theory of Uniform Distribution of sequences to Functional Analysis and then drawing inspiration from the consequent results, we study concepts and results in Uniform Distribution itself. So let $E$ be a Banach space. Then we prove:\\ (a) If $F$ is a bounded subset of $E$ and $x \in \overline{\co}(F)$ (= the closed convex hull of $F$), then there is a sequence $(x_n) \subseteq F$ which is Cesàro summable to $x$.\\ (b) If $E$ is separable, $F \subseteq E^*$ bounded and $f \in \overline{\co}^{w^*}(F)$, then there is a sequence $(f_n) \subseteq F$ whose sequence of arithmetic means $\frac{f_1+\dots+f_N}{N}$, $N \ge 1$ weak$^*$-converges to $f$. By the aid of the Krein-Milman theorem, both (a) and (b) have interesting implications for closed, convex and bounded subsets $Ω$ of $E$ such that $Ω=\overline{\co}(\ex Ω)$ and for weak$^*$ compact and convex subsets of $E^*$. Of particular interest is the case when $Ω=B_{C(K)^*}$, where $K$ is a compact metric space. By further expanding the previous ideas and results, we are able to generalize a classical theorem of Uniform Distribution which is valid for increasing functions $φ:I=[0,1] \rightarrow \mathbb{R}$ with $φ(0)=0$ and $φ(1)=1$, for functions $φ$ of bounded variation on $I$ with $φ(0)=0$ and total variation $V_0^1 φ=1$.
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