一类常宽"等腰梯形"

本文由对角线等于底边长的等腰梯形构造了一类新的常宽“等腰梯形”, 而著名的常宽凸集圆盘与Reuleaux 三角形为退化的特例. 我们还证明了关于这类常宽“等腰梯形” 面积的Blaschke-Lebesgue定理.     

平面常宽凸域的不对称性度量

通过引入刻画平面常宽凸域的不对称性函数,证明了在平面常宽凸域中,圆域 是最对称的,而Reuleaux三角形是最不对称的．     

平面常宽凸体的构造

该文首先定义了一类平面曲线"杠杆轮"与它的臂函数,并利用臂函数给出杠杆轮的参数表示.其次,证明了杠杆轮是平面常宽曲线的一种等价刻画.最后,表明Reuleaux多边形是臂函数为分段常函数的一类杠杆轮,进而构造出偶数边的Reuleaux多边形.     

凸集的广义Reuleaux三角形

常宽凸集的面积最小者为Reulaux三角形，而非常宽凸集的面积最小者为何呢？它就是本文将给出的广义Reuleaux三角形△R。     

$\varOmega$-凸集的组合与结构性质[英文]

本文研究$\varOmega$-凸集的组合性质和结构性质. 在一定条件下, 证明关于$\varOmega$-凸集的Randon型定理, Helly型定理. Caratheodory型定理以及Minkowski型定理, 并举例说明对一般的$\varOmega$-凸集这些定理不一定成立. 文中所得结果是关于凸集的这些类型定理的推广, 同时也为有关$\varOmega$-凸函数的研究提供了理论工具.     

广义凸拓扑线性空间集值优化的ε-强有效解

在Hausdorff局部凸拓扑线性空间中考虑约束集值优化问题(VP)的ε-强有效性.在内部锥类凸假设下,利用凸集分离定理,分别建立了关于ε-强有效解的标量化定理和ε-Lagrange乘子定理.     

集值映象的不动点定理

本文讨论了定义在仿紧凸集上的集值映象的有关性质,并由此得到了集值映象的平衡点和不动点存在性的若干充分条件,推广了一些已有的结果.     

关于上半连续性和Kakutani不动点定理

本文给出了集值映象的弱上半连续而非准上半连续的例子,证明了对于闭凸的集值映象弱上半连续和准上半连续等价,并把Kakutani不动点定理推广到非闭凸的弱上半连续的情形.     

拓扑线性空间中的Drop定理与Drop性质

给出了拓扑线性空间中的一个Drop定理.利用此Drop定理,证明了拓扑线性空间中的每个序列紧凸集具有Drop性质;每个可数紧闭凸集具有拟Drop性质.而且结出了拓扑线性空间中Drop性质和拟Drop性质的序列流特征.也讨论了Drop性质和拟Drop性质与泛函取极值之间的联系.     

集值映射全局真有效次梯度下的Moreau-Rockafellar定理

本文研究了集值映射的Moreau-Rockafellar型定理的问题.利用集值映射弱次梯度的Moreau-Rockafellar定理,在内部(锥)-凸条件下,获得了集值映射关于全局真有效性的Moreau-Rockafellar型定理结果,推广了集值映射在锥-凸假设下的Moreau-Rockafellar型定理的结果,所得结论深化和丰富了最优化理论的内容.     

On convex bodies of constant width

We present an alternative proof of the following fact: the hyperspace of compact closed subsets of constant width in Rn is a contractible Hilbert cube manifold. The proof also works for certain subspaces of compact convex sets of constant width as well as for the pairs of compact convex sets of constant relative width. Besides, it is proved that the projection map of compact closed subsets of constant width is not 0-soft in the sense of Shchepin, in particular, is not open.     

A characterization of the Euclidean ball in terms of concurrent sections of constant width

We prove that the Euclidean ball is the unique convex body with the property that all its sections through a fixed point are convex bodies of constant width. Furthermore, we characterize those convex bodies which are sections of convex bodies of constant width.Research supported by the Alexander von Humboldt-Foundation.     

Some Computational Aspects of Geodesic Convex Sets in a Simple Polygon

In this article, we deal with some computational aspects of geodesic convex sets. Motzkin-type theorem, Radon-type theorem, and Helly-type theorem for geodesic convex sets are shown. In particular, given a finite collection of geodesic convex sets in a simple polygon and an “oracle,” which accepts as input three sets of the collection and which gives as its output an intersection point or reports its nonexistence; we present an algorithm for finding an intersection point of this collection.     

A surjectivity theorem for differential operators on spaces of regular functions

In this article we show that it is possible to construct a Koszul-type complex for maps given by suitable pairwise commuting matrices of polynomials. This result has applications to surjectivity theorems for constant coefficients differential operators of finite and infinite order. In particular, we construct a large class of constant coefficients differential operators which are surjective on the space of regular (or monogenic) functions on open convex sets.     

The Convexity and the Gaussian Curvature Estimates for the Level Sets of Harmonic Functions on Convex Rings in Space Forms

In this paper, we first establish a constant rank theorem for the second fundamental form of the convex level sets of harmonic functions in space forms. Applying the deformation process, we prove that the level sets of the harmonic functions on convex rings in space forms are strictly convex. Moreover, we give a lower bound for the Gaussian curvature of the convex level sets of harmonic functions in terms of the Gaussian curvature of the boundary and the norm of the gradient on the boundary.     

On Some Generalized Polyhedral Convex Constructions

Generalized polyhedral convex sets, generalized polyhedral convex functions on locally convex Hausdorff topological vector spaces, and the related constructions such as sum of sets, sum of functions, directional derivative, infimal convolution, normal cone, conjugate function, subdifferential are studied thoroughly in this paper. Among other things, we show how a generalized polyhedral convex set can be characterized through the finiteness of the number of its faces. In addition, it is proved that the infimal convolution of a generalized polyhedral convex function and a polyhedral convex function is a polyhedral convex function. The obtained results can be applied to scalar optimization problems described by generalized polyhedral convex sets and generalized polyhedral convex functions.     

Stability for the Minkowski measure of convex domains of constant width

In 1988, H. Groemer gave a stability theorem for the area of convex domains of constant width. In this paper, we obtain a stability theorem for the well-known Minkowski measure of asymmetry for convex domains of constant width.     

On evolutoids of planar convex curves

There are many interesting curves which we can associate with a given convex curve, however, in this work we are especially interested in studying the relations between the given curve and its evolutoids: that is, the curve obtained as the envelope of lines making a fixed angle with the normal line at every point of the curve. The first result is an inequality between the area enclosed by the given curve and the area enclosed by its evolutoid. Also, we proved that a convex curve is of constant width (centrally symmetric) if and only if its evolutoid for a fixed angle is of constant width (centrally symmetric).     

Power-law estimates for the central limit theorem for convex sets

We investigate the rate of convergence in the central limit theorem for convex sets established in [B. Klartag, A central limit theorem for convex sets, Invent. Math., in press. [8]]. We obtain bounds with a power-law dependence on the dimension. These bounds are asymptotically better than the logarithmic estimates which follow from the original proof of the central limit theorem for convex sets.