一类无穷矩阵变换的刻划

对于一类经典的矢值序列空间,引入了一类重要子集,它包括了该序列空间的全部全有界集和许多非全有界集.利用Antosik-Mikusinski基本矩阵定理和该子集族,获得了一个无穷矩阵收敛定理,进而给出了一类经典无穷矩阵变换的刻划.     

一类矢值序列空间上的矩阵变换定理

对于一类经典的矢值序列空间,文中引入一类重要子集,它包括了该序列空间的全部有界集和许多非有界集.利用Antosik-Mikusinski基本矩阵定理和该子集族,获得了一个无穷矩阵收敛定理,并且给出了一类经典无穷矩阵变换的更强刻画.此结果改进了算子级数序列赋值收敛定理.     

算子级数的序列赋值收敛性

对于巴拿赫空间上的经典矢量值序列空间,引入了一类重要的子集,它包含了该序列空间中的全部金有界集.利用该子集,得到了一个算子级数序列赋值收敛定理.完全去掉了通常对算予的线性约束.它不仅在理论上很重要,而且也增加了应用的可能性.     

Banach空间中关于有界集的同时远达问题的适定性

本文研究Banach空间中关于有界集的同时远达问题的适定性,在集合的Hausdorff距离下,证明了：对自反局部一致凸Banach空间中的闭有界集K,使所有关于K的同时远达问题是适定的紧凸子集A全体在紧凸子集全体中是Gδ型集．     

有界集空间中的几乎Chebyshev子集

研究了有界集关于一般集合的限制Chebyshev中心的存在唯一性。在集合的Hausdorff距离下,引进了有界集空间中的几乎Chebyshev子集的概念。证明了一致凸(自反局部一致凸)Banach空间中的任何闭子集都是关于有界集(紧凸子集)的几乎Chebyshev子集。     

一类二阶微分方程无穷边值问题的可解性

研究了一类无穷区间上非线性二阶微分方程两点边值问题解的存在性.首先在连续函数空间中引入算子T,并证明了T是全连续算子,然后利用Banach空间上全连续算子的不动点定理等方法,得到了这类边值问题存在有界解的一个充分条件,从而证明了一类无穷区间上非线性二阶微分方程两点边值问题的可解性,文末举例说明了定理的可行性.     

由Cantor展式定义的Besicovitch-Eggleston子集

本文研究了由Cantor展式所确定的一类Besicovitch-Eggleston子集.应用Billingsley定理,得到了这类集合的维数.并且表明无穷符号空间和有限符号空间上的Besicovitch-Eggleston子集的性质是有区别的.     

关于Echelon空间无穷矩阵变换集的有界性

无穷矩阵变换是研究序列空间理论的重要工具.研究一个空间到另一个空间无穷矩阵变换的形式,是序列空间理论中的重要内容,并且已有众多工作.本文将进一步研究一般的Echelon空间到空间l^p(1≤p≤∞),c、c₀的无穷矩阵变换集的有界性.所得结果的特例正是Echelon空间到l^p(1≤p≤∞)c、c₀无穷矩阵变换的形式,同时概括了前人的许多结果.     

全变差有界函数列的一致(R)可积性

给出了一致有界单调函数列一致可积性定理 ,由此得出全变差序列有界的收敛函数列的一致可积性 .说明了该结论可判断一些非一致收敛函数列的逐项积分性质 .     

B值随机变量序列的一类局部收敛定理

研究取值于Banach空间随机变量序列的一类局部收敛定理．作为推论,得到了一类B值鞅差序列的极限定理和经典的独立随机变量序列的极限定理,     

Determinant preserving maps: an infinite dimensional version of a theorem of Frobenius

In this paper we investigate the structure of maps on classes of Hilbert space operators leaving the determinant of linear combinations invariant. Our main result is an infinite dimensional version of the famous theorem of Frobenius about determinant preserving linear maps on matrix algebras. In this theorem of ours, we use the notion of (Fredholm) determinant of bounded Hilbert space operators which differ from the identity by an element of the trace class. The other result of the paper describes the structure of those transformations on sets of positive semidefinite matrices which preserve the determinant of linear combinations with fixed coefficients.     

Surjectivity and invertibility properties of totally positive matrices

A new “finite section” type theorem is used to show that the members of an interesting class of bounded totally positive matrices map l_∞ onto l_∞ if and only if their range contains a vector which alternates in sign and has coordinates bounded away from zero. The class of matrices studied contains all banded totally positive matrices, and thus all infinite spline collocation matrices. Connections to related work and extension to matrices which are not sign regular are indicated.     

An Analog of Titchmarsh’s Theorem for the Fourier–Walsh Transform

The space clos(X) of all nonempty closed subsets of an unbounded metric space X is considered. The space clos(X) is endowed with a metric in which a sequence of closed sets converges if and only if the distances from these sets to a fixed point θ are bounded and, for any r, the sequence of the unions of the given sets with the exterior balls of radius r centered at θ converges in the Hausdorff metric. The metric on clos(X) thus defined is not equivalent to the Hausdorff metric, whatever the initial metric space X. Conditions for a set to be closed, totally bounded, or compact in clos(X) are obtained; criteria for the bounded compactness and separability of clos(X) are given. The space of continuous maps from a compact space to clos(X) is considered; conditions for a set to be totally bounded in this space are found.     

Constructing bounded remainder sets and cut-and-project sets which are bounded distance to lattices

For any irrational cut-and-project setup, we demonstrate a natural infinite family of windows which gives rise to separated nets that are each bounded distance to a lattice. Our proof provides a new construction, using a sufficient condition of Rauzy, of an infinite family of non-trivial bounded remainder sets for any totally irrational toral rotation in any dimension.     

Krein Orthogonal Entire Matrix Functions and Related Lyapunov Equations: A State Space Approach

For a class of entire matrix valued functions of exponential type new necessary and sufficient conditions are derived in order that these functions are Krein orthogonal functions. The conditions are stated in terms of certain operator Lyapunov equations. These equations arise by using infinite dimensional state space representations of the entire matrix functions involved. As a corollary, using a recent operator inertia theorem, we give a new proof of the Ellis-Gohberg-Lay theorem which relates the number of zeros of a Krein orthogonal function in the open upper half plane to the number of negative eigenvalues of the corresponding selfadjoint convolution operator.     

ON THE SPH-DISTRIBUTION CLASS

Following up Neuts‘ idea, the SPH-distribution class associated with bounded Q matrices for infinite Markov chains is defined. The main result in this paper is to characterize the SPH class through the derivatives of the distribution functions. Based on the characterization theorem, closure properties, the expansion, uniform approximation,and the matrix representations of the SPH class are also discussed by the derivatives of the distribution functions at origin.Key words Phase type distribution, absorbing Markov chain, operator theory, SPH- distribution, properties     

On the pointwise domination of a function by its maximal function

We show that under rather general circumstances the almost everywhere pointwise inequality \(|f|(x) \le Mf (x)\) is equivalent to a weak form of the conclusion of the Lebesgue density theorem for totally bounded closed sets. We derive both positive and negative results from this characterization.     

Compactness in the spaces of variable integrability and summability

We study totally bounded sets in the spaces of variable integrability and summability. The full characterization of these sets is given. Furthermore, the Sudakov theorem in the setting of the mixed Lebesgue sequence spaces is proven.