内容简介
Though its title "Integral Geometry" may appear somewhat unusual in thiscontext it is nevertheless quite appropriate, for Integral Geometry is anoutgrowth of what in the olden days was referred to as "geometric probabil-ities."
Originating, as legend has it, with the Buffon needle problem (which afternearly two centuries has lost little of its elegance and appeal), geometricprobabilities have run into difficulties culminating in the paradoxes ofBertrand which threatened the fledgling field with banishment from the homeof Mathematics. In rescuing it from this fate, Poincar6 made the suggestionthat the arbitrariness of definition underlying the paradoxes could be removedby tying closer the definition of probability with a geometric group of which itwould have to be an invariant.
内页插图
目录
Editors Statement
Foreword
Preface
Chapter 1. Convex Sets in the Plane
1. Introduction
2. Envelope of a Family of Lines
3. Mixed Areas of Minkowski
4. Some Special Convex Sets
5. Surface Area of the Unit Sphere and Volume of the Unit Ball
6. Notes and Exercises
Chapter 2. Sets of Points and Poisson Processes in the Plane
1. Density for Sets of Points
2. First Integral Formulas
3. Sets of Triples of Points
4. Homogeneous Planar Poisson Point Processes
5. Notes
Chapter 3. Sets of Lines in the Plane
1. Density for Sets of Lines
2. Lines That Intersect a Convex Set or a Curve
3. Lines That Cut or Separate Two Convex Sets
4. Geometric Applications
5. Notes and Exercises
Chapter 4. Pairs of Points and Pairs of Lines
1. Density for Pairs of Points
2. Integrals for the Power of the Chords of a Convex Set.
3. Density for Pairs of Lines
4. Division of the Plane by Random Lines
5. Notes
Chapter 5. Sets of Strips in the Plane
1. Density for Sets of Strips
2. Buffons Needle Problem
3. Sets of Points, Lines, and Strips
4. Some Mean Values
5. Notes
Chapter 6. The Group of Motions in the Plane: Kinematic Density .
1. The Group of Motions in the Plane
2. The Differential Forms on 9Jl
3. The Kinematic Density
4. Sets of Segments
5. Convex Sets That Intersect Another Convex Set
6. Some Integral Formulas
7. A Mean Value; Coverage Problems
8. Notes and Exercises
Chapter 7. Fundamental Formulas of Poinear~ and Blaschke
1. A New Expression for the Kinematic Density
2. Poincar6s Formula
3. Total Curvature of a Closed Curve and of a Plane Domain
4. Fundamental Formula of Blaschke
5. The lsoperimetric Inequality .
6. Hadwigers Conditions for a Domain to Be Able to Contain Another
7. Notes
Chapter 8. Lattices of Figures
1. Definitions and Fundamental Formula
2. Lattices of Domains
3. Lattices of Curves
4. Lattices Of Points
5. Notes and Exercise
Chapter 9. Differential Forms and Lie Groups
1. Differential Forms
2. Pfaffian Differential Systems
3. Mappings of Differentiable Manifolds
4. Lie Groups; Left and Right Translations
5. Left-lnvariant Differential Forms
6. Maurer-Cartan Equations
7. lnvariant Volume Elements of a Group: Unimodular Groups
8. Notes and Exercises
Chapter 10. Density and Measure in Homogeneous Spaces
1. Introduction
2. invariant Subgroups and Quotient Groups
3. Other Conditions for the Existence of a Density on Homo-geneous Spaces
4. Examples
5. Lie Transformation Groups
6. Notes and Exercises
Chapter 11. The Affine Groups
1. The Groups of Affine Transformations
2. Densities for Linear Spaces with Respect to Special Homo-geneous Affinities
3. Densities for Linear Subspaces with Respect to the SpecialNonhomogeneous Affine Group
4. Notes and Exercises
Chapter 12. The Group of Motions in E,
1. Introduction
2. Densities for Linear Spaces in E
3. A Differential Formula
4. Density for r-Planes about a Fixed q-Plane
5. Another Form of the Density for r-Planes in
6. Sets of Pairs of Linear Spaces
7. Notes
Chapter 13. Convex Sets in
1. Convex Sets and Quermassintegrale
2. Cauchys Formula
3. Parallel Convex Sets; Steiners Formula
4. Integral Formulas Relating to the Projections of a Convex Set on Linear Subspaces
5. Integrals of Mean Curvature
6. Integrals of Mean Curvature and Quermassintegrale.
7. Integrals of Mean Curvature of a Flattened Convex Body
8. Notes
Chapter 14. Linear Subspaces, Convex Sets, and Compact Manifolds
1. Sets of r-Planes That Intersect a Convex Set
2. Geometric Probabilities
3. Croftons Formulas in En
4. Some Relations between Densities of Linear Subspaces
5. Linear Subspaces That Intersect a Manifold
6. Hypersurfaces and Linear Spaces
7. Notes
Chapter 15. The Kinematic Density in E
1. Formulas on Densities
2. Integral of the Volume
3. A Differential Formula
4. The Kinematic Fundamental Formula
5. Fundamental Formula for Convex Sets
6. Mean Values for the Integrals of Mean Curvature
7. Fundamental Formula for Cylinders
8. Some Mean Values
9. Lattices in En.
10. Notes and Exercise
Chapter 16. Geometric and Statistical Applications; Stereology
1. Size Distribution of Particles Derived from the Size Distribution of Their Sections
2. Intersection with Random Planes
3. Intersection with Random Lines
4. Notes
Chapter 17. Noneuclidean Integral Geometry
1. The n-Dimensional Noneuclidean Space
2. The Gauss-Bonnet Formula for Noneuclidean Spaces
3. Kinematic Density and Density for r-Planes
4. Sets of r-Planes That Meet a Fixed Body
5. Notes
Chapter 18. Croftons Formulas and the Kinematic Fundamental Formula
in Noneuclidean Spaces
1. Croftons Formulas
2. Dual Formulas in Elliptic Space
3. The Kinematic Fundamental Formula in Noneuclidean
Spaces
4. Steiners Formula in Noneuclidean Spaces
5. An Integral Formula for Convex Bodies in Elliptic Space
6. Notes
Chapter 19. Integral Geometry and Foliated Spaces; Trends in Integral Geometry
1. Foliated Spaces
2. Sets of Geodesics in a Riemann Manifold
3. Measure of Two-Dimensional Sets of Geodesics
4. Measure of (2n - 2)-Dimensional Sets of Geodesics
5. Sets of Geodesic Segments
6. Integral Geometry on Complex Spaces
7. Symplectic Integral Geometry
8. The Integral Geometry of Gelfand
9. Notes
Appendix. Differential Forms and Exterior Calculus
1. Differential Forms and Exterior Product
2. Two Applications of the Exterior Product
3. Exterior Differentiation
4. Stokes Formula
5. Comparison with Vector Calculus in Euclidean Three-Dimensional Space
6. Differential Forms over Manifolds
Bibliography and References
Author Index
Subiect Index
前言/序言
This monograph is the first in a projected series on Probability Theory.
Though its title "Integral Geometry" may appear somewhat unusual in thiscontext it is nevertheless quite appropriate, for Integral Geometry is anoutgrowth of what in the olden days was referred to as "geometric probabil-ities."
Originating, as legend has it, with the Buffon needle problem (which afternearly two centuries has lost little of its elegance and appeal), geometricprobabilities have run into difficulties culminating in the paradoxes ofBertrand which threatened the fledgling field with banishment from the homeof Mathematics. In rescuing it from this fate, Poincar6 made the suggestionthat the arbitrariness of definition underlying the paradoxes could be removedby tying closer the definition of probability with a geometric group of which itwould have to be an invariant.
Thus a union of concepts was born that was to become Integral Geometry. It is unfortunate that in the past forty or so years during which ProbabilityTheory experienced its most spectacular rise to mathematical prominence,Integral Geometry has stayed on its fringes. Only quite recently has there beena reawakening of interest among practitioners of Probability Theory in thisbeautiful and fascinating branch of Mathematics, and thus the book byProfessor Santal6, for many years the undisputed leader in the field of IntegralGeometry, comes at a most appropriate time. Complete and scholarly, the book also repeatedly belies the popular beliefthat applicability and elegance are incompatible. Above all the book should remind all of us that Probability Theory ismeasure theory with a "soul" which in this case is provided not by Physics or bygames of chance or by Economics but by the most ancient and noble of allof mathematical disciplines, namely Geometry.
概率的几何叙事:从测度到宇宙结构 本书深入探讨了一个迷人且深刻的数学交叉领域——几何概率。它不仅仅是对经典概率论的简单延伸,而是一种全新的视角,将概率论的抽象概念植根于我们对空间、形状和测量的直觉之中。全书的叙事线索在于如何使用几何工具,特别是积分几何的强大框架,来量化和分析随机现象在连续空间中的表现。 我们将从基础的测度论和拓扑学概念出发,为后续的几何概率论奠定坚实的理论基础。这里不涉及微积分的繁琐细节,而是聚焦于“可测集”的本质,以及黎曼积分和勒贝格积分在描述不规则区域上的概率分布时的优势。读者将理解为什么在处理高维空间或复杂形体时,经典的计数方法会失效,而引入积分测度是必然的趋势。 第一部分:欧氏空间中的随机点与线 本部分的核心在于二维和三维欧氏空间中点、线、平面以及更一般形体的统计行为。我们首先考察随机选择一个点落在给定区域内的概率问题。这看似简单,实则引出了对“均匀分布”的严谨定义。当区域变得复杂,比如一个不规则的凸多边形,我们如何定义其内部的随机点分布,以及如何计算其概率密度函数?书中将详细分析这些基础构造,并引入几何概率密度函数(GPDF)的概念,它彻底取代了离散概率论中的频率概念。 随后,我们将转向更具挑战性的随机直线和随机平面的主题。著名的布丰投针问题(Buffon’s Needle Problem)将被作为起点,但我们不会止步于此。更重要的是,我们将探讨如何定义空间中“随机直线族”的度量。这需要引入运动不变量(kinematic invariant)的概念——即一个度量如何保持不变,无论我们如何平移或旋转(刚体运动)我们所考察的系统。通过对旋转和平移群的理解,我们将推导出线与线之间相交的概率,以及一条随机直线穿过一个给定形状轮廓的长度期望。这部分内容将为理解物理学中的散射问题和材料科学中的结构分析打下基础。 第二部分:积分几何学的核心工具箱 积分几何是连接分析学、微分几何和概率论的桥梁。本部分将系统地介绍支撑该理论的两大核心支柱:外测度(Outer Measure)和运动测度(Measure of Motion)。 在传统的几何学中,我们使用长度、面积、体积来衡量形体。然而,在积分几何中,我们需要衡量“形体集合”的集合。例如,在所有可能的圆形中,随机选择一个半径在 $r$ 到 $r+dr$ 之间,圆心在某个区域 $D$ 内的圆的集合的“大小”是多少?我们不能用传统的面积或体积来度量,因为圆形是二维形体,而圆心集合是二维点集,它们在四维参数空间($x, y, r, heta$)中形成一个元素。 运动测度 $mu(K)$ 的引入,提供了一种在 $n$ 维空间中,对所有通过刚体运动变换得到的形体 $K$ 的集合进行积分的方法。书中将详尽推导二维和三维空间中平面、圆形、凸体等的运动测度公式。这些公式不仅具有深刻的数学美感,更重要的是,它们是计算几何概率的“积分因子”。 我们还将深入探讨Crofton 公式及其推广。Crofton 公式揭示了形状的几何特性(如周长、面积)与其在随机直线族中的积分特性之间的深刻联系。通过在随机直线族上对某个凸体进行积分,我们可以反推出该凸体的周长。这体现了概率测度与确定性几何量之间的二元对偶关系。 第三部分:随机几何与几何概率的应用前沿 在掌握了基础的积分几何工具后,本书将目光投向这些理论在现代科学中的具体应用,这些应用往往涉及高维随机过程和非欧几何的初步探索。 随机凸体与随机集合 我们探讨随机凸集的形成过程。例如,随机在平面上投掷许多小的凸体(如圆盘或椭圆),并将它们的凸包取出,这个最终形成的随机凸包的期望面积和期望周长是多少?这需要利用Minkowski泛函数和相关函数来处理凸体之间的相互作用。书中会分析不同生成机制(如:由随机点构成的凸包,或随机增长模型)下,随机凸体几何属性的统计规律。 概率在微分几何中的体现 几何概率论自然地过渡到微分几何。在曲面上(例如球面或黎曼流形)上,如何定义“随机”?在这些空间中,平移和旋转的意义发生了变化,我们需要依赖于测地线(Geodesics)来代替直线。书中将分析在曲面上随机选取两条测地线相交的概率问题,并展示如何将欧氏空间的运动不变量推广到一般的黎曼流形上。这部分内容为理解广义相对论中时空随机几何的可能性提供了理论基础。 空间结构的统计描述 最后,我们将关注随机点过程在空间中的应用,特别是在描述宇宙学、材料微观结构和空间网络中的随机分布。我们采用泊松点过程(Poisson Point Process)作为分析框架,研究随机点集合的可见性问题——例如,在一个随机点云中,从任意一个点能“看到”其他点的概率是多少?这涉及到对随机视域(random horizon)的分析。通过积分几何的工具,我们可以计算出在给定的随机点密度下,空间中任意两点之间存在无遮挡连线的概率。 本书的结构设计旨在引导读者从直观的概率概念出发,逐步攀升到严谨的积分几何理论,最终展示如何利用这些抽象工具来解决具体的、涉及连续空间测量的难题。全书强调的是对“随机形体”进行积分的艺术,而非仅仅是计算一个离散事件的频率。它是一部关于如何用几何的语言来书写概率的专著。