Evgenii Safronenko
This paper is devoted to measures of symmetry based on distance between centroid and one of the centers of John and Lowner ellipsoid. The author proves the accuracy of the derived upper bounds for the considered measures of symmetry.
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A convex body K has associated with it a unique circumscribed ellipsoid CE(K) with minimum volume, and a unique inscribed ellipsoid IE(K) with maximum volume. We first give a unified, modern exposition of the basic theory of these extremal ellipsoids using the semi-infinite programming approach pioneered by Fritz John in his seminal 1948 paper. We then investigate the automorphism groups of convex bodies and their extremal ellipsoids. We show that if the automorphism group of a convex body K is large enough, then it is possible to determine the extremal ellipsoids CE(K) and IE(K) exactly, usin…
We prove new Alexandrov-Fenchel type inequalities and new affine isoperimetric inequalities for mixed $p$-affine surface areas. We introduce a new class of bodies, the illumination surface bodies, and establish some of their properties. We show, for instance, that they are not necessarily convex. We give geometric interpretations of $L_p$ affine surface areas, mixed $p$-affine surface areas and other functionals via these bodies. The surprising new element is that not necessarily convex bodies provide the tool for these interpretations.
Abstract In this paper, we study affine bodies of revolution. This will allow us to prove that a convex body all whose orthogonal $n$-projections are affinely equivalent is an ellipsoid, provided $n\equiv 0,1, 2$ mod $4$, $n>1$ with the possible exemption of $n=133$. Our proof uses convex geometry and topology of compact Lie groups. AMS classification subject: 22E10, 52A05
We give geometric interpretations of certain affine invariants of convex bodies. The affine invariants are the p-affine surface areas introduced by Lutwak. The geometric interpretations involve generalizations of the Santaló-bodies introduced by the authors in a previous paper.
Extremal sections and projections of certain convex bodies: a survey
本文综述了$\ell_p$球等凸体在低维子空间上截面与投影体积的极值估计，回顾了源于数的几何的概率与分析方法的进展。
Extremal affine surface areas in a functional setting
本文在函数空间中引入极值仿射表面积，建立其对偶公式，证明其与函数积分幂成正比，从而推广并改进了凸体情形的相关结果。
The affine subspace concentration inequality for centered convex bodies
本文针对中心对称凸体建立了Wu提出的线性子空间集中不等式的仿射版本，将Wu等人关于多胞体的结果推广到了凸体。
New approach to affine Moser-Trudinger inequalities via Besov polar projection bodies
本文利用 Besov 极投影体的仿射不变量，将 $W^{s,p}$ 函数的仿射不等式推广至 $p\geq n/s$，得到更强的 Moser-Trudinger 与 Morrey 型结果，并建立相应 BBM 不等式。
Extending Blaschke and Lebesgue's classical result in the Euclidean plane, it has been recently proved in spherical and the hyperbolic cases, as well, that Reuleaux triangles have the minimal area among convex domains of constant width $D$. We prove an essentially optimal stability version of this statement in each of the three types of surfaces of constant curvature. In addition, we summarize the fundamental properties of convex bodies of constant width in spaces of constant curvature, and provide a characterization in the hyperbolic case in terms of horospheres.
This paper is dedicated to the Orlicz-Petty bodies. We first propose the homogeneous Orlicz affine and geominimal surface areas, and establish their basic properties such as homogeneity, affine invariance and affine isoperimetric inequalities. We also prove that the homogeneous geominimal surface areas are continuous, under certain conditions, on the set of convex bodies in terms of the Hausdorff distance. Our proofs rely on the existence of the Orlicz-Petty bodies and the uniform boundedness of the Orlicz-Petty bodies of a convergent sequence of convex bodies. Similar results for the nonhomog…
We prove sharp inequalities for the average number of affine diameters through the points of a convex body $K$ in ${\mathbb R}^n$. These inequalities hold if $K$ is either a polytope or of dimension two. An example shows that the proof given in the latter case does not extend to higher dimensions.
Affine chord Sobolev inequalities and radial mean bodies for functions
本文通过仿射弦Sobolev不等式推导出函数径向平均体的仿射等周不等式，并推广了几何径向平均体的单调性性质。
John-type decompositions for affinely-optimal positions of convex bodies
本文提出了一种约翰型分解，用于确定凸体在仿射最优位置下的必要条件，并应用于Banach-Mazur距离的优化问题。
We show that the Banach-Mazur distance between the parallelogram and the affine-regular hexagon is $\frac{3}{2}$ and we conclude that the diameter of the family of centrally-symmetric planar convex bodies is just $\frac{3}{2}$. A proof of this fact does not seem to be published earlier. Asplund announced this without a proof in his paper proving that the Banach-Mazur distance of any planar centrally-symmetric bodies is at most $\frac{3}{2}$. Analogously, we deal with the Banach-Mazur distances between the parallelogram and the remaining affine-regular even-gons.
Affine Isoperimetric Inequalities for Higher-Order Projection and Centroid Bodies
本文将Schneider的m阶差分体思想推广至投影体、质心体和径向平均体，证明多类仿射等周不等式，并给出有界变差函数的m阶仿射Sobolev不等式。
Random polytopes in convex bodies: Bridging the gap between extremal containers
本研究探讨块β分布族中随机点凸包构成的随机多面体的渐近性质，建立面期望数量的显式增长率，分析均匀分布下任意维度面的期望数量及体积差，揭示其插值性质以弥合两类凸容器中随机多面体行为的差距。
We extend the definition of the centroid body operator to an Orlicz--Lorentz centroid body operator on the star bodies in $\mathbb R^n$, and establish the sharp affine isoperimetric inequality that bounds (from below) the volume of the Orlicz--Lorentz centroid body of any convex body containing the origin in its interior by the volume of this convex body.
The Orlicz-Brunn-Minkowski theory receives considerable attention recently, and many results in the $L_p$-Brunn-Minkowski theory have been extended to their Orlicz counterparts. The aim of this paper is to develop Orlicz $L_ϕ$ affine and geominimal surface areas for single convex body as well as for multiple convex bodies, which generalize the $L_p$ (mixed) affine and geominimal surface areas -- fundamental concepts in the $L_p$-Brunn-Minkowski theory. Our extensions are different from the general affine surface areas by Ludwig (in Adv. Math. 224 (2010)). Moreover, our definitions for Orlicz $…
Extremal Banach-Mazur distance between a symmetric convex body and an arbitrary convex body on the plane
本文证明在平面上，若对称凸体与另一凸体的Banach-Mazur距离达到极值2，则该凸体必为三角形。
The Alexandrov-Fenchel inequality, a far-reaching generalization of the classical isoperimetric inequality to arbitrary mixed volumes, lies at the heart of convex geometry. The characterization of its extremal bodies is a long-standing open problem that dates back to Alexandrov's original 1937 paper. The known extremals already form a very rich family, and even the fundamental conjectures on their general structure, due to Schneider, are incomplete. In this paper, we completely settle the extremals of the Alexandrov-Fenchel inequality for convex polytopes. In particular, we show that the extre…
Let K be a convex body in $R^d$. A random polytope is the convex hull $[x_1,...,x_n]$ of finitely many points chosen at random in K. $\Bbb E(K,n)$ is the expectation of the volume of a random polytope of n randomly chosen points. I. Bárány showed that we have for convex bodies with $C^3$ boundary and everywhere positive curvature $$ c(d)\lim_{n \to \infty} \frac {vol_d(K)-\Bbb E(K,n)}{(\frac{vol_d(K)}{n})^{\frac{2}{d+1}}} =\int_{\partial K} κ(x)^{\frac{1}{d+1}}dμ(x) $$ where $κ(x)$ denotes the Gauß-Kronecker curvature. We show that the same formula holds for all convex bodies if $κ(x)$ denotes…
In this paper, we introduce several mixed $L_p$ geominimal surface areas for multiple convex bodies for all $p\neq -n$. Our definitions are motivated from an equivalent formula for the mixed $p$-affine surface area. Some properties, such as the affine invariance, for these mixed $L_p$ geominimal surface areas are proved. Related inequalities, such as, Alexander-Fenchel type inequality, Santaló style inequality, affine isoperimetric inequalities, and cyclic inequalities are established. Moreover, we also study some properties and inequalities for the $i$-th mixed $L_p$ geominimal surface areas …
This paper aims to develop basic theory for the dual Orlicz $L_ϕ$ affine and geominimal surface areas for star bodies, which belong to the recent dual Orlicz-Brunn-Minkowski theory for star bodies. Basic properties for these new affine invariants will be provided. Moreover, related Orlicz affine isoperimetric inequality, cyclic inequality, Santaló style inequality and Alexander-Fenchel type inequality are established.
It is proved that if $C$ is a convex body in ${\Bbb R}^n$ then $C$ has an affine image $\widetilde C$ (of non-zero volume) so that if $P$ is any 1-codimensional orthogonal projection, $$|P\widetilde C| \ge |\widetilde C|^{n-1\over n}.$$ It is also shown that there is a pathological body, $K$, all of whose orthogonal projections have volume about $\sqrt{n}$ times as large as $|K|^{n-1\over n}$.
Tightening Inequalities on Volume Extremal $k$-Ellipsoids Using Asymmetry Measures
本文利用 John 不对称性统一并加强了关于低维椭球体积上下界的两类不等式，证明其在大维度、平面及任意不对称性凸体（含交叉多胞形、平行多胞形和单纯形）中的紧性，并给出与 Banach-Mazur 距离相关的推论。
A stability version of the Blaschke-Santaló inequality and the affine isoperimetric inequality for convex bodies of dimension n>2 is proved. The first step is the reduction to the case when the convex body is o-symmetric and has axial rotational symmetry. This step works for related inequalities compatible with Steiner symmetrization. Secondly, for these convex bodies, a stability version of the characterization of ellipsoids by the fact that each hyperplane section is centrally symmetric is established.
The $L_p$-floating area, curvature entropy, and isoperimetric inequalities on the sphere
该研究将欧氏几何中的$L_p$-仿射表面积等概念推广到球面空间，引入球面凸体的$L_p$-浮动面积与曲率熵，证明相关等周不等式、对偶公式与单调性，并推广到非负常曲率空间形式。
We prove that the reciprocal of the volume of the polar bodies, about the Santaló point, of a {\em shadow system} of convex bodies $K_t$, is a convex function of $t$. Thus extending to the non-symmetric case a result of Campi and Gronchi. The case that the reciprocal of the volume is an affine function of $t$ is also investigated and is characterized under certain conditions. We apply these results to prove exact reverse Santaló inequality for polytopes in $\rd{d}$ that have at most $d+3$ vertices.
A classification of SL$(n)$ contravariant, continuous function valued valuations on convex bodies is established. Such valuations are natural extensions of SL$(n)$ contravariant $L_p$ Minkowski valuations, the classification of which characterized $L_p$ projection bodies, which are fundamental in the $L_p$ Brunn-Minkowski theory, for $p \geq 1$. Hence our result will help to better understand extensions of the $L_p$ Brunn-Minkowski theory. In fact, our results characterize general projection functions which extend $L_p$ projection functions ($p$-th powers of the support functions of $L_p$ proj…
Anisotropic symmetrization, convex bodies, and isoperimetric inequalities
本文利用各向异性等周不等式、Sobolev 函数精细性质及 Brunn-Minkowski 理论，给出各向异性 Pólya-Szegö 型不等式无需逼近论证的新证明，并实现对极值函数的刻画。
Floating bodies for ball-convex bodies
本文在球凸体类中引入浮动体，通过其体积右导数定义相对仿射表面积，并证明该量为刚体运动不变量及上半连续赋值。
The Fourier transform of planar convex bodies and discrepancy over intervals of rotations
本文研究了平面凸体特征函数在仿射变换下平均的Fourier变换，建立了基于几何性质的上下界，并给出了仿射二次偏差渐近行为的精确结果，回答了Bilyk和Mastrianni的公开问题。
New fiber and graph combinations of convex bodies
本文提出凸体的三种新组合（$L_p$ 纤维、弦和图组合），推广 Steiner 对称化，证明 Brunn-Minkowski 型不等式及广义仿射表面积的凹凸性，并推导 Minkowski 第一不等式。
Floating bodies and duality in spaces of constant curvature
该研究在d维球面、双曲、de Sitter等常曲率空间中构造p-仿射表面积的自然类似物，证明其为对偶共轭非欧凸体浮动体的体积导数，建立了由常曲率控制的实解析统一框架，揭示了其与欧氏空间两类曲率测度的关联。
On star-convex bodies with rotationally invariant sections
本文证明，满足光滑边界且所有过原点超平面截面为仿射旋转体的原点对称星凸体，自身必为仿射旋转体，从而肯定回答了一个近期提出的问题。
Small perturbations of polytopes
本文研究凸体无穷小扰动的泛函分析刻画，完整描述了多胞体情形下的可实现扰动集合，并由此给出迷向常数多胞体极大化子的必要条件。
In this paper we formulate and solve extremal problems in the d-dimensional Euclidean space and further in hypergraphs, originating from problems in stoichiometry and elementary linear algebra. The notion of affine simplex is the bridge between the original problems and the presented extremal theorem on set systems. A function related to Sperners theorem and the YBLM inequality is also considered and its relation to hypergraph Turan problems is discussed.
The affine quermassintegrals associated to a convex body in $\mathbb{R}^n$ are affine-invariant analogues of the classical intrinsic volumes from the Brunn-Minkowski theory, and thus constitute a central pillar of affine convex geometry. They were introduced in the 1980's by E. Lutwak, who conjectured that among all convex bodies of a given volume, the $k$-th affine quermassintegral is minimized precisely on the family of ellipsoids. The known cases $k=1$ and $k=n-1$ correspond to the classical Blaschke-Santaló and Petty projection inequalities, respectively. In this work we confirm Lutwak's c…
Let $K$ be a convex body in ${\bf R}^n$ and $B$ be the Euclidean unit ball in ${\bf R}^n$. We show that $$\mbox{lim}_{t\rightarrow 0} \frac{|K| -|K_t|}{|B| - |B_t|}= \frac{as(K)}{as(B)},$$ where $as(K)$ respectively $as(B)$ is the affine surface area of $K$ respectively $B$ and $\{K_t\}_{t\geq 0}$, $\{B_t\}_{t\geq 0}$ are general families of convex bodies constructed from $K$, $B$ satifying certain conditions. As a corollary we get results obtained in [M-W], [Schm],[S-W] and[W].
We prove a conjecture of B. Grünbaum stating that the set of affine invariant points of a convex body equals to the set of points invariant under all affine linear symmetries of the convex body. As a consequence we give a short proof on the fact that the affine space of affine linear points is infinite dimensional. In particular, we show that the set of affine invariant points with no dual is of second category. We investigate extremal cases for a class of symmetry measures. We show that the center of the John and Löwner ellipsoid can be far apart and we give the optimal order for the extremal…
It is proved that every convex body in the plane has a point such that the union of the body and its image under reflection in the point is convex. If the body is not centrally symmetric, then it has, in fact, three affinely independent points with this property.
On Sections of Convex Bodies in John's Position and of Generalised $B_p^n$ Balls
本文通过结合几何Brascamp-Lieb不等式与广义Parseval型恒等式，改进了K.Ball的论证，为约翰位置下凸体截面体积提供了精确估计，并推广了Meyer-Pajor和Koldobsky关于$B_p^n$球体极值截面的经典估计。
In this paper, the isodiametric problem for centrally symmetric convex bodies in the Euclidean d-space R^d containing no interior non-zero point of a lattice L is studied. It is shown that the intersection of a suitable ball with the Dirichlet-Voronoi cell of 2L is extremal, i.e., it has minimum diameter among all bodies with the same volume. It is conjectured that these sets are the only extremal bodies, which is proved for all three dimensional and several prominent lattices.
Convex bodies with all characteristics planar
该研究针对辛空间ℝ²ⁿ（n>1）中的光滑强凸体，证明了满足所有特征线或所有外弹子球轨迹为平面这一条件的凸体，均为球的仿射辛映像。
In this note we prove a more general (and topological) version of Grünbaum's conjecture about affine invariant points. As an application of our result we show that, if we consider the action of the group of similarities, Grünbaum's conjecture remains valid in other families of convex sets (not necessarily convex bodies).
Negative moments of the support function and applications to isotropic convex bodies
本文通过支撑函数的负矩估计和球冠论证，研究各向同性凸体的随机投影内半径等几何量，得到多项式偏差估计并证明立方体在无条件类中的极值性，同时给出混合旋转-投影定理和体积剖面的尖锐结果。
All upper semicontinuous and SL(n) invariant valuations on convex bodies containing the origin in their interiors are completely classified. Each such valuation is shown to be a linear combination of the Euler characteristic, the volume, the volume of the polar body, and the recently discovered Orlicz surface areas.
This text is a somewhat reformatted (e.g., some statements that were not as such in the original paper, are given the names "Corollary" or "Theorem.") translation of the old and practically inaccessible paper: P. Kuchment, On the question of the affine-invariant points of convex bodies, (in Russian), Optimizacija No. 8(25) (1972), 48--51, 127. MR0350621. There partial solutions of some old problems of B. Grünbaum concerning affine-invariant points of convex bodies were obtained. The main restriction, due to which the solution was incomplete, was the compactness restriction on the group of line…
We prove that for any compact set B in R^d and for any epsilon >0 there is a finite subset X of B of |X|=d^{O(1/epsilon^2)} points such that the maximum absolute value of any linear function ell: R^d --> R on X approximates the maximum absolute value of ell on B within a factor of epsilon sqrt{d}. We also discuss approximations of convex bodies by projections of spectrahedra, that is, by projections of sections of the cone of positive semidefinite matrices by affine subspaces.
On the Fourier Mean Bodies of a Convex Body
本文引入凸体K的傅里叶p次平均体F_pK，通过傅里叶变换连接径向p次平均体R_pK，证明傅里叶反演公式，并研究其仿射几何性质、凸性范围及与相交体的关系。
We study a new construction of bodies from a given convex body in $\mathbb{R}^{n}$ which are isomorphic to (weighted) floating bodies. We establish several properties of this new construction, including its relation to $p$-affine surface areas. We show that these bodies are related to Ulam's long-standing floating body problem which asks whether Euclidean balls are the only bodies that can float, without turning, in any orientation.
Elementary equivalence of convex bodies in affine and projective languages
研究紧致凸体在仿射和射影语言下的初等等价性，通过可定义紧致度量族等方法证明任意维度凸体在\(L_{\mathrm{aff}}\)中初等等价当且仅当仿射等价，还发展了\(L_B\)演算及得出相关结果并分类非紧致例子。
We investigate the weighted $L_p$ affine surface areas which appear in the recently established $L_p$ Steiner formula of the $L_p$ Brunn Minkowski theory. We show that they are valuations on the set of convex bodies and prove isoperimetric inequalities for them. We show that they are related to $f$ divergences of the cone measures of the convex body and its polar, namely the Kullback-Leibler divergence and the Rényi-divergence.
We carry out a systematic investigation on floating bodies in real space forms. A new unifying approach not only allows us to treat the important classical case of Euclidean space as well as the recent extension to the Euclidean unit sphere, but also the new extension of floating bodies to hyperbolic space. Our main result establishes a relation between the derivative of the volume of the floating body and a certain surface area measure, which we called the floating area. In the Euclidean setting the floating area coincides with the well known affine surface area, a powerful tool in the affine…
An $r^{\an}$-center of a compact body $\Om$ in an $n$ dimensional Euclidean space is a point that gives an extremal value of the regularized Riesz potential, which is the (Hadamard regularization of) integration on $\Om$ of the distance from the point to the power $\an$. We show that for any real number $\la$ if a compact body is sufficiently close to a ball in the sense of asphericity then the $r^{\an}$-center is unique. We also study the regularized potentials of a unit ball.
In 1978, Makai Jr. established a remarkable connection between the volume-product of a convex body, its maximal lattice packing density and the minimal density of a lattice arrangement of its polar body intersecting every affine hyperplane. Consequently, he formulated a conjecture that can be seen as a dual analog of Minkowski's fundamental theorem, and which is strongly linked to the well-known Mahler-conjecture. Based on the covering minima of Kannan & Lovász and a problem posed by Fejes Tóth, we arrange Makai Jr.'s conjecture into a wider context and investigate densities of lattice arrange…
Empirical forms of the Petty projection inequality
本文从随机视角重新审视Petty投影不等式，建立了其多种经验形式，并针对随机凸集的混合投影体与混合体积等泛函推导出尖锐极值不等式。
On Bezdek's conjecture for high-dimensional convex bodies with an aligned center of symmetry
本文在高维空间中验证了Bezdek猜想，假设通过固定点的截面具有反射轴，且互补不变子空间平行于固定超平面，证明了在正交和仿射设置中成立。
The Extremals of Minkowski's Quadratic Inequality
本文通过将任意凸体的混合体积表示为与高度退化椭圆算子相关联的Dirichlet形式，利用算子的定量刚性性质，完全解决了Minkowski二次不等式的极值问题并证实了R. Schneider的猜想。
We discuss the notions of circumradius, inradius, diameter, and minimum width in generalized Minkowski spaces (that is, with respect to gauges), i.e., we measure the "size" of a given convex set in a finite-dimensional real vector space with respect to another convex set. This is done via formulating some kind of containment problem incorporating homothetic bodies of the latter set or strips bounded by parallel supporting hyperplanes thereof. The paper can be seen as a theoretical starting point for studying metrical problems of sets in generalized Minkowski spaces.
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