Mathieu Meyer, Elisabeth Werner
Motivated by the Blaschke-Santaló inequality, we define for a convex body K in ${\bf R}^n$ and for $t \in {\bf R}$ the Santaló-regions S(K,t) of K. We investigate properties of these sets and relate them to a concept of Affine Differential Geometry, the affine surface area of K.
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Mahler's conjecture asks whether the cube is a minimizer for the volume product of a body and its polar in the class of symmetric convex bodies in R^n. The corresponding inequality to the conjecture is sometimes called the the reverse Blaschke-Santalo inequality. The conjecture is known in dimension two and in several special cases. In the class of unconditional convex bodies, Saint Raymond confirmed the conjecture, and Meyer and Reisner, independently, characterized the equality case. In this paper we present a stability version of these results and also show that any symmetric convex body, w…
This paper is dedicated to study the sine version of polar bodies and establish the $L_p$-sine Blaschke-Santaló inequality for the $L_p$-sine centroid body. The $L_p$-sine centroid body $Λ_p K$ for a star body $K\subset\mathbb{R}^n$ is a convex body based on the $L_p$-sine transform, and its associated Blaschke-Santaló inequality provides an upper bound for the volume of $Λ_p^{\circ}K$, the polar body of $Λ_p K$, in terms of the volume of $K$. Thus, this inequality can be viewed as the "sine cousin" of the $L_p$ Blaschke-Santaló inequality established by Lutwak and Zhang. As $p\rightarrow \inf…
Regular ellipsoids and a Blaschke-Santaló-type inequality for projections of non-symmetric convex bodies
本文将 Pisier 关于覆盖数正则递减的定理推广至非对称凸体，通过引入关于 Santaló 点位于原点的凸体投影的 Blaschke-Santaló 型不等式作为关键新方法，并探讨了其在各向同性凸体平均范数中的应用。
The Blaschke-Santaló Inequality is the assertion that the volume product of a centrally symmetric convex body in Euclidean space is maximized by (and only by) ellipsoids. In this paper we give a Fourier analytic proof of this fact.
We establish new functional versions of the Blaschke-Santaló inequality on the volume product of a convex body which generalize to the non-symmetric setting an inequality of K. Ball and we give a simple proof of the case of equality. As a corollary, we get some inequalities for $\log$-concave functions and Legendre transforms which extend the recent result of Artstein, Klartag and Milman, with its equality case.
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.
It is shown that each monotone Minkowski endomorphism of convex bodies gives rise to an isoperimetric inequality which directly implies the classical Urysohn inequality. Among this large family of new inequalities, the only affine invariant one - the Blaschke-Santaló inequality - turns out to be the strongest one. A further extension of these inequalities to merely weakly monotone Minkowski endomorphisms is proven to be impossible. Moreover, for functional analogues of monotone Minkowski endomorphisms, a family of analytic inequalities for log-concave functions is established which generalizes…
We present a complete 3-dimensional Blaschke-Santaló diagram for planar convex bodies with respect to the four classical magnitudes inner and outer radius, diameter and (minimal) width in euclidean spaces.
In 1940, Luis Santaló proved a Helly-type theorem for line transversals to boxes in R^d. An analysis of his proof reveals a convexity structure for ascending lines in R^d that is isomorphic to the ordinary notion of convexity in a convex subset of R^{2d-2}. This isomorphism is through a Cremona transformation on the Grassmannian of lines in P^d, which enables a precise description of the convex hull and affine span of up to d ascending lines: the lines in such an affine span turn out to be the rulings of certain classical determinantal varieties. Finally, we relate Cremona convexity to a new c…
We explore an interplay between an analysis of diffusion flows such as Ornstein--Uhlenbeck flow and Fokker--Planck flow and inequalities from convex geometry regarding the volume product. More precisely, we introduce new types of hypercontractivity for the Ornstein--Uhlenbeck flow and clarify how these imply the Blaschke--Santaló inequality and the inverse Santaló inequality, also known as Mahler's conjecture. Motivated the link, we establish two types of new hypercontractivity in this paper. The first one is an improvement of Borell's reverse hypercontractivity inequality in terms of Nelson's…
We present proofs of the reverse Santaló inequality, the existence of M-ellipsoids and the reverse Brunn-Minkowski inequality, using purely convex geometric tools. Our approach is based on properties of the isotropic position.
We prove the Blaschke-Santaló inequality restricted to $n$-gons: the extremal polygons are the affine regular $n$-gons. If either the John or the Löwner ellipse of a planar $o$-symmetric convex body $K$ is the unit circle about $o$, then a sharpening of the Blaschke-Santaló inequality holds: even the aritmetic mean $\left( V(K) + V( K^*) \right) /2 $ is at least $π$. We give stability variants of the Blaschke-Santaló inequality for the plane. If for some $n \ge 3$ the planar convex body $K$ is $n$-fold rotationally symmetric about $o$, then we give the exact maximum of $V(K^*)$, as a function …
A strengthening of the Blaschke-Santaló inequality for $o$-symmetric planar convex bodies
本文加强了$o$-对称平面凸体的Blaschke-Santaló不等式，给出了具有最优阶次误差项的新不等式。
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.
On the conjectured capillary Blaschke-Santaló inequality
本文证明当θ∈(0,π/2)时，猜想的毛细Blaschke-Santaló不等式对任何无条件严格凸毛细超曲面成立，并指出当θ∈(π/2,π)时毛细体积乘积无上界。
Narrowing the gaps of the missing Blaschke-Santaló diagrams
本文提出了几个关于平面凸体几何量之间新的精确不等式，缩小了缺失的平面Blaschke-Santaló图间隙，并将部分不等式通过替换几何量扩展至更高维度。
The Santaló point for the Holmes-Thompson boundary area
本文探讨赋范空间中凸体Holmes-Thompson边界面积的Santaló点，在范数为$C^1$及单位球与凸体重合时证明了其存在性与唯一性，并在单位球光滑正曲率时给出对偶Santaló点。
H. Guggenheimer generalized the planar volume product problem for locally convex curves $C$ enclosing the origin $k \ge 2$ times. He conjectured that the minimal volume product $V(C)V(C^*)$ for these curves is attained if the curve consists of the longest diagonals of a regular $(2k+1)$-gon, with centre $0$, these diagonals taken always in the positive orientation. This conjectured minimum is of the form $k^2 + O(k)$. We investigate special cases of this conjecture. We prove it for locally convex $n$-gons with $2k+1 \le n \le 4k$, if the central angles at $0$ of all sides are equal to $2k π/n$…
Jung-type Inequalities and Blaschke-Santaló Diagrams for Different Diameter Variants
本文研究了关于凸体的圆外径与直径的几何不等式，涉及内径和Minkowski不对称性。不同凸体直径定义在非对称度量下会分解，对应于度量的不同对称化方法。
Blaschke--Santaló inequalities with respect to costs
该论文研究内积替换为代价的泛函Blaschke–Santaló不等式，结合卦限不等式与Steiner对称化给出充分条件，推导乘性代价相关的Brascamp–Lieb不等式改进及Fradelizi–Meyer定理的L^p版本，还分析了具体代价的亏缺分解等内容。
A sharp Santaló inequality in a slab with centrally symmetric sections
本文证明了一个尖锐的Santaló型不等式，通过射影对应转化为板条中凸体的体积乘积上界问题，并分类了极值情形，同时给出了一维函数不等式族。
On a Blaschke-Santaló-type inequality for $r$-ball bodies
本文针对 $r$-球体给出 Blaschke-Santaló 型不等式的新证明，并证明了极大值点的唯一性，同时提及应用与相关问题。
On Ball's conjectured Santaló type inequality
本文证明了对对称各向同性凸体K，Ball猜想的关于内积二次矩的Santaló型不等式成立，等号成立当且仅当K为欧氏球，并给出了Blaschke-Santaló不等式的渐近最优稳定性版本。
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…
In this paper, we prove that, if functions (concave) $ϕ$ and (convex) $ψ$ satisfy certain conditions, the $L_ϕ$ affine surface area is monotone increasing, while the $L_ψ$ affine surface area is monotone decreasing under the Steiner symmetrization. Consequently, we can prove related affine isoperimetric inequalities, under certain conditions on $ϕ$ and $ψ$, without assuming that the convex body involved has centroid (or the Santaló point) at the origin.
In 1944, Santaló asked about the average number of normals through a point of a given convex body. Since then, numerous results appeared in the literature about this problem. The aim of this paper is to give a concise summary of these results, with some new, recent developments. We point out connections of this problem to static equilibria of rigid bodies as well as to geometric partial differential equations of surface evolution.
Duality and Heat flow
本研究揭示凸函数勒让德变换与热流演化的关系及其在泛函布拉施克-桑塔洛不等式的应用，并描述了该不等式的局部极大值点。
Sections and projections of the outer and inner regularizations of a convex body
本文建立了比较重心或Santaló点在原点的凸体与其内、外正则化体截面和投影体积的新几何不等式，并推广至对数凹函数，方法依赖于Bizeul和Klartag的最优$M$-估计。
Uncentered Blaschke-Santaló inequalities for the Gaussian measure
本研究探讨高斯测度下广义体积乘积的极大化问题，证明极大化者为凸体，并给出低维精确形式及高维微分方程描述，同时明确欧几里得单位球唯一极大化的参数范围。
A purely analytic proof is given for an inequality that has as a direct consequence the two most important affine isoperimetric inequalities of plane convex geometry: The Blaschke-Santalo inequality and the affine isoperimetric inequality of affine differential geometry.
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 …
On the polar of Schneider's difference body
本文证明了Schneider差体极体的体积由椭球最大化，推广了Blaschke-Santaló不等式，并渐近证明了Schneider猜想。
Minimization of the inradius of convex bodies for prescribed diameter and circumradius in Minkowski spaces
研究任意维Minkowski空间中内径、外接半径和直径的Blaschke-Santaló图，通过四个线性不等式和一个更复杂的不等式描述边界，分析填充边界的凸体及范数类型导致边界退化为单点的情况。
In this paper a Blaschke-Santaló diagram involving the area, the perimeter and the elastic energy of planar convex bodies is considered. More precisely we give a description of set $$\mathcal{E}:=\left\{(x,y)\in \R^2, x=\frac{4πA(Ω)}{P(Ω)^2},y=\frac{E(Ω)P(Ω)}{2π^2},\,Ω\mbox{convex} \right\},$$ where $A$ is the area, $P$ is the perimeter and $E$ is the elastic energy, that is a Willmore type energy in the plane. In order to do this, we investigate the following shape optimization problem: $$\min_{Ω\in\mathcal{C}}\{E(Ω)+μA(Ω)\},$$ where $\mathcal{C}$ is the class of convex bodies with fixed peri…
We find that for any n-dimensional, compact, convex subset K of R^{n+1} there is an affinely-spherical hypersurface M in R^{n+1} with center at the relative interior of K, such that the disjoint union of M and K is the boundary of an (n+1)-dimensional, compact, convex set. This so-called affine hemisphere M is uniquely determined by K up to affine transformations, it is of elliptic type, is associated with K in an affinely-invariant manner, and it is centered at the Santalo point of K.
We explore connections furnished by the Funk metric, a relative of the Hilbert metric, between projective geometry, billiards, convex geometry and affine inequalities. We first show that many metric invariants of the Funk metric are invariant under projective transformations as well as projective duality. These include the Holmes-Thompson volume and surface area of convex subsets, and the length spectrum of their boundary, extending results of Holmes-Thompson and Álvarez Paiva on Schäffer's dual girth conjecture. We explore in particular Funk billiards, which generalize hyperbolic billiards in…
A new trick for for Santalo's integral geometric proof of the strong Bonnesen inequality
本文通过引入“平均技巧”平衡被积函数的正负区域，证明了Bonnesen泛函在最小宽度圆环内外半径区间上非负，从而为强Bonnesen不等式提供了新的积分几何证明，并应用于曲线缩短流的最终形状分析。
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。
Let $K$ be a convex body in $\mathbb R^n$. We prove that in small codimensions, the sections of a convex body through the centroid are quite symmetric with respect to volume. As a consequence of our estimates we give a positive answer to a problem posed by M. Meyer and S. Reisner regarding convex intersection bodies.
It is well known that any planar convex body $A$ permits to inscribe an affine-regular hexagon $H_A$. We prove that the centroid of $A$ belongs to the homothetic image of $H_A$ with ratio $\frac{4}{21}$ and the center in the center of $H_A$. This ratio cannot be enlarged.
We show that there is a constant $D \approx 0.2016$ such that for every $n$, every convex body $K\subset \mathbb R^n$, and every hyperplane $H\subset \mathbb R^n$, the distance between the projection of the centroid of $K$ onto $H$ and the centroid of the projection of $K$ onto $H$ is at most $D$ times the width of $K$ in the direction of the segment connecting the two points. The constant $D$ is asymptotically sharp.
In this paper, we introduce the $L_p$ geominimal surface area for all $-n\neq p<1$, which extends the classical geominimal surface area ($p=1$) by Petty and the $L_p$ geominimal surface area by Lutwak ($p>1$). Our extension of the $L_p$ geominimal surface area is motivated by recent work on the extension of the $L_p$ affine surface area -- a fundamental object in (affine) convex geometry. We prove some properties for the $L_p$ geominimal surface area and its related inequalities, such as, the affine isoperimetric inequality and a Santaló style inequality. Cyclic inequalities are established to…
Let $K \subset \mathbb R^n$ be a convex body with barycenter at the origin. We show there is a simplex $S \subset K$ having also barycenter at the origin such that $\left(\frac{vol(S)}{vol(K)}\right)^{1/n} \geq \frac{c}{\sqrt{n}},$ where $c>0$ is an absolute constant. This is achieved using stochastic geometric techniques. Precisely, if $K$ is in isotropic position, we present a method to find centered simplices verifying the above bound that works with very high probability. As a consequence, we provide correct asymptotic estimates on an old problem in convex geometry. Namely, we show that th…
Given any real numbers $1<p<q$, we study the norm ratio (i.e. the ratio between the $q$-norm and the $p$-norm) of marginals of centered convex bodies. We first show that some marginal of the simplex maximizes said ratio in the class of $n$-dimensional centered convex bodies. We then pass to the dimension independent (i.e. log-concave) case where we find a 1-parameter family of random variables in which the maximum ratio must be attained, and find the exact maximizer of the ratio when $p=2$ and $q$ is even. In addition, we find another interesting maximization property of marginals of the simpl…
In this paper, we give an overview of some results concerning best and random approximation of convex bodies by polytopes. We explain how both are linked and see that random approximation is almost as good as best approximation.
A convexity point of a convex body is a point with the property that the union of the body and its reflection in the point is convex. It is proved that in the plane a typical convex body (in the sense of Baire category) has infinitely many convexity points. The proof makes use of the `middle hedgehog' of a planar convex body $K$, which is the curve formed by the midpoints of all affine diameters of $K$. The stated result follows from the fact that for a typical planar convex body the convex hull of the middle hedgehog has infinitely many exposed points.
We prove a sharp Rogers-Shephard type inequality for the p-difference body of a convex body in the two-dimensional case, for every p greater than or equal to one.
Higher-Order Lp Isoperimetric and Sobolev Inequalities
本研究将凸几何中的维数间算子推广至$L^p$情形，把单纯形拓展为任意含原点的m维凸体，建立了多类m阶$L^p$等周与仿射Sobolev不等式，并给出了线性泛函算子范数体积的等周不等式应用。
Motivated by conjectures of Mahler and Makai Jr., we study bounds on the volume of a convex body in terms of the successive minima of its polar body.
In this paper, we obtain some results about the mean curvature integrals of the outer parallel convex body of constant width.
The aim of this note is to investigate the properties of the convex hull and the homothetic convex hull functions of a convex body $K$ in Euclidean $n$-space, defined as the volume of the union of $K$ and one of its translates, and the volume of $K$ and a translate of a homothetic copy of $K$, respectively, as functions of the translation vector. In particular, we prove that the convex hull function of the body $K$ does not determine $K$. Furthermore, we prove the equivalence of the polar projection body problem raised by Petty, and a conjecture of G.Horváth and Lángi about translative constan…
We show that in all dimensions d>2, there exists an asymmetric convex body of revolution all of whose maximal hyperplane sections have the same volume. This gives the negative answer to the question posed by V. Klee in 1969.
We present a probabilistic model of illuminating a convex body by independently distributed light sources. In addition to recovering C.A. Rogers' upper bounds for the illumination number, we improve previous estimates of J. Januszewski and M. Naszódi for a generalized version of the illumination parameter.
One of the fundamental results in Convex Geometry is Busemann's theorem, which states that the intersection body of a symmetric convex body is convex. Thus, it is only natural to ask if there is a quantitative version of Busemann's theorem, i.e., if the intersection body operation actually improves convexity. In this paper we concentrate on the symmetric bodies of revolution to provide several results on the (strict) improvement of convexity under the intersection body operation. It is shown that the intersection body of a symmetric convex body of revolution has the same asymptotic behavior ne…
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。
The purpose of this paper is to answer the following question: If all hyperplane sections through the origin of a convex body are "equal", is the convex body "equal" to the ball? The meaning of the notion "equal" will change in the course of this paper. Similarly, we are interested in the following problem: If all orthogonal projections of a convex body onto hyperplanes are "equal", is the convex body "equal" to the ball? Topology and convex geometry are deeply interrelated in the solution and understanding of these problems.
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.
In this work we study the fencing problem consisting of finnding a trisection of a 3-rotationally symmetric planar convex body which minimizes the maximum relative diameter. We prove that an optimal solution is given by the so-called standard trisection. We also determine the optimal set giving the minimum value for this functional and study the corresponding universal lower bound.
Giving a joint generalization of a result of Brazitikos, Chasapis and Hioni and results of Giannopoulos and Milman, we prove that roughly $\left\lceil \frac{d}{(1-\vartheta)^d}\ln\frac{1}{(1-\vartheta)^d} \right\rceil$ points chosen uniformly and independently from a centered convex body $K$ in ${\mathbb R}^d$ yield a polytope $P$ for which $\vartheta K\subseteq P\subseteq K$ holds with large probability. The proof is simple, and relies on a combinatorial tool, the $\varepsilon$-net theorem.
On the maximal distance between the centers of mass of a planar convex body and its boundary
本文研究平面凸体与其边界的质心距离，证明该距离不超过直径的1/6和边界长度的1/12，且常数最优。
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