内容简介
Representation theory is concerned with the ways of writing a groupas a group of matrices. Not only is the theory beautiful in its own right,but it also provides one of the keys to a proper understanding of finitegroups. For example, it is often vital to have a concrete description of aparticular group; this is achieved by finding a representation of thegroup as a group of matrices. Moreover, by studying the differentrepresentations of the group, it is possible to prove results which lieoutside the framework of representation theory. One simple example: allgroups of order p2 (where p is a prime number) are abelian; this can beshown quickly using only group theory, but it is also a consequence ofbasic results about representations.
内页插图
目录
Preface
1 Groups and homomorphisms
2 Vector spaces and linear transformations
3 Group representations
4 FG-modules
5 FG-submodules and reducibility
6 Group algebras
7 FG-homomorphisms
8 Maschke's Theorem
9 Schur's Lemma
10 Irreducible modules and the group algebra
11 More on the group algebra
12 Conjugacy classes
13 Characters
14 Inner products of characters
15 The number of irreducible characters
16 Character tables and orthogonality relations
17 Normal subgroups and lifted characters
18 Some elementary character tables
19 Tensor products
20 Restriction to a subgroup
21 Induced modules and characters
22 Algebraic integers
23 Real representations
24 Summary of properties of character tables
25 Characters of groups of order pq
26 Characters of some p-groups
27 Character table of the simple group of order 168
28 Character table of GL(2, q)
29 Permutations and characters
30 Applications to group theory
31 Burnside's Theorem
32 An application of representation theory to molecular vibration
Solutions to exercises
Bibliography
Index
前言/序言
We have attempted in this book to provide a leisurely introduction tothe representation theory of groups. But why should this subjectinterest you?
Representation theory is concerned with the ways of writing a groupas a group of matrices. Not only is the theory beautiful in its own right,but it also provides one of the keys to a proper understanding of finitegroups. For example, it is often vital to have a concrete description of aparticular group; this is achieved by finding a representation of thegroup as a group of matrices. Moreover, by studying the differentrepresentations of the group, it is possible to prove results which lieoutside the framework of representation theory. One simple example: allgroups of order p2 (where p is a prime number) are abelian; this can beshown quickly using only group theory, but it is also a consequence ofbasic results about representations. More generally, all groups of order (p and q primes) are soluble; this again is a statement purely aboutgroups, but the best proof, due to Burnside, is an outstanding exampleof the use of representation theory. In fact, the range of applications ofthe theory extends far beyond the boundaries of pure mathematics, andincludes theoretical physics and chemistry - we describe one suchapplication in the last chapter. The book is suitable for students who have taken first undergraduatecourses involving group theory and linear algebra. We have included twopreliminary chapters which cover the necessary background material.The basic theory of representations is developed in Chapters 3-23, andour methods concentrate upon the use of modules; although this accordswith the more modem style of algebra, in several instances our proofsdiffer from those found in other textbooks. The main results are elegantand surprising.
现代代数与结构探索:群论、环论与域论的深度解析 本书旨在为数学、物理学及计算机科学领域的学生和研究人员提供一个全面、深入且富有启发性的现代代数基础。它聚焦于代数结构的核心——群、环和域,旨在构建坚实的理论框架,并展示这些抽象结构在不同数学分支中的强大应用。全书结构严谨,论证清晰,力求在保持数学严谨性的同时,兼顾读者的理解需求。 第一部分:群论的基石与深入 本书的开篇将系统地介绍群(Groups)的基本概念、定义和核心性质。我们将从最基础的二元运算、封闭性、结合律、单位元和逆元开始,逐步引入有限群与无限群的区分。 子群与陪集: 详细探讨子群(Subgroups)的结构性质,特别是正规子群(Normal Subgroups)的引入,它是理解商群(Quotient Groups)的桥梁。陪集(Cosets)的概念将被深入分析,特别是拉格朗日定理(Lagrange's Theorem)——群论中的里程碑式成果——的推导及其在有限群分析中的关键作用将被详尽阐述。 同态与同构: 群之间的映射,即群同态(Group Homomorphisms)与同构(Isomorphisms),是理解不同群之间内在联系的关键。本书将重点讲解同态定理(Isomorphism Theorems),特别是第一同态定理,它揭示了商群与同态像之间的本质联系。同构的判定标准和具体的例子分析将贯穿始终。 群的作用与应用: 群作用(Group Actions)是连接抽象代数与具体问题的强大工具。我们将介绍群在集合上的作用,核心概念如轨道(Orbits)和稳定子(Stabilizers)。通过应用伯恩赛德引理(Burnside's Lemma),我们将展示如何利用群作用解决计数问题,例如对不同涂色方案的计数。 特殊结构的群: 对于一些重要的群结构,如循环群(Cyclic Groups)、有限阿贝尔群(Finite Abelian Groups)的分类结构,以及对称群(Symmetric Groups $S_n$)和二面体群(Dihedral Groups $D_n$)的详细分析,将为后续更复杂的结构研究打下坚实基础。 第二部分:环论的拓展与深入 在建立了对群论的深刻理解之后,本书将顺理成章地转向环(Rings)的代数结构。环的引入不仅增加了运算的复杂性,更使其成为描述代数方程和数论问题的理想框架。 环的基本概念与性质: 环的定义、交换环(Commutative Rings)与非交换环的区分,以及单位元(Unity)的存在性被清晰界定。特殊的元素,如零因子(Zero Divisors)、幂零元(Nilpotent Elements)和幂等元(Idempotent Elements),将被一一剖析。 子环与理想: 类似于群中的子群,环中对应的结构是子环(Subrings)。更重要的是理想(Ideals)的概念,它在环论中扮演着与正规子群在群论中相似的关键角色。左理想、右理想和双边理想的定义和关系将被深入探讨。 商环与同态: 商环(Quotient Rings)的构造将基于理想的概念进行,并引出环同态(Ring Homomorphisms)和环同构定理。这部分内容将强调如何将环的结构分解,类似于群论中的分解。 特殊类型的环: 书中将重点分析积分域(Integral Domains)、域(Fields)和除环(Division Rings)。域作为最“良好”的环结构,其性质和在多项式理论中的应用将被详尽介绍。我们将对特征(Characteristic)进行精确定义和分类。 素理想与极大理想: 引入素理想(Prime Ideals)和极大理想(Maximal Ideals)的概念,它们是构建域和确定环结构的重要工具。通过分析这些理想,读者将掌握如何从更基本的元素构造出更复杂的结构。 第三部分:域论的几何与代数连接 第三部分将聚焦于域(Fields)的理论,这是连接纯代数与几何、分析的关键领域,尤其在伽罗瓦理论(Galois Theory)的准备阶段至关重要。 多项式环与因式分解: 在一个域上的多项式环(Polynomial Rings over a Field)是域论的核心研究对象。我们将详细分析多项式的除法算法、最大公约式、以及不可约多项式的概念。对于单变量多项式环,我们将证明其具有唯一因式分解的性质(Unique Factorization Domains, UFDs)。 域的扩张: 域扩张(Field Extensions)是本部分的核心。定义了扩张域、次数(Degree of Extension)以及代数元(Algebraic Elements)和超越元(Transcendental Elements)。我们将深入研究扩域的构造,特别是通过根(Roots)的添加来构造新的域。 分裂域与最小多项式: 最小多项式(Minimal Polynomial)的唯一性和重要性将被证明。在此基础上,分裂域(Splitting Fields)的概念被引入,它为理解多项式根的结构提供了精确的框架。 结构性总结: 本书的最终目标是为读者提供一个清晰的、相互关联的代数框架。从群的对称性到环的运算规律,再到域的扩张结构,这些理论共同构成了现代数学分析和建模的基石。全书配备了大量的例题和习题,旨在培养读者独立解决问题的能力和对抽象代数本质的深刻洞察力。