內容簡介
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.
內頁插圖
目錄
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.
現代代數與結構探索:群論、環論與域論的深度解析 本書旨在為數學、物理學及計算機科學領域的學生和研究人員提供一個全麵、深入且富有啓發性的現代代數基礎。它聚焦於代數結構的核心——群、環和域,旨在構建堅實的理論框架,並展示這些抽象結構在不同數學分支中的強大應用。全書結構嚴謹,論證清晰,力求在保持數學嚴謹性的同時,兼顧讀者的理解需求。 第一部分:群論的基石與深入 本書的開篇將係統地介紹群(Groups)的基本概念、定義和核心性質。我們將從最基礎的二元運算、封閉性、結閤律、單位元和逆元開始,逐步引入有限群與無限群的區分。 子群與陪集: 詳細探討子群(Subgroups)的結構性質,特彆是正規子群(Normal Subgroups)的引入,它是理解商群(Quotient Groups)的橋梁。陪集(Cosets)的概念將被深入分析,特彆是拉格朗日定理(Lagrange's Theorem)——群論中的裏程碑式成果——的推導及其在有限群分析中的關鍵作用將被詳盡闡述。 同態與同構: 群之間的映射,即群同態(Group Homomorphisms)與同構(Isomorphisms),是理解不同群之間內在聯係的關鍵。本書將重點講解同態定理(Isomorphism Theorems),特彆是第一同態定理,它揭示瞭商群與同態像之間的本質聯係。同構的判定標準和具體的例子分析將貫穿始終。 群的作用與應用: 群作用(Group Actions)是連接抽象代數與具體問題的強大工具。我們將介紹群在集閤上的作用,核心概念如軌道(Orbits)和穩定子(Stabilizers)。通過應用伯恩賽德引理(Burnside's Lemma),我們將展示如何利用群作用解決計數問題,例如對不同塗色方案的計數。 特殊結構的群: 對於一些重要的群結構,如循環群(Cyclic Groups)、有限阿貝爾群(Finite Abelian Groups)的分類結構,以及對稱群(Symmetric Groups $S_n$)和二麵體群(Dihedral Groups $D_n$)的詳細分析,將為後續更復雜的結構研究打下堅實基礎。 第二部分:環論的拓展與深入 在建立瞭對群論的深刻理解之後,本書將順理成章地轉嚮環(Rings)的代數結構。環的引入不僅增加瞭運算的復雜性,更使其成為描述代數方程和數論問題的理想框架。 環的基本概念與性質: 環的定義、交換環(Commutative Rings)與非交換環的區分,以及單位元(Unity)的存在性被清晰界定。特殊的元素,如零因子(Zero Divisors)、冪零元(Nilpotent Elements)和冪等元(Idempotent Elements),將被一一剖析。 子環與理想: 類似於群中的子群,環中對應的結構是子環(Subrings)。更重要的是理想(Ideals)的概念,它在環論中扮演著與正規子群在群論中相似的關鍵角色。左理想、右理想和雙邊理想的定義和關係將被深入探討。 商環與同態: 商環(Quotient Rings)的構造將基於理想的概念進行,並引齣環同態(Ring Homomorphisms)和環同構定理。這部分內容將強調如何將環的結構分解,類似於群論中的分解。 特殊類型的環: 書中將重點分析積分域(Integral Domains)、域(Fields)和除環(Division Rings)。域作為最“良好”的環結構,其性質和在多項式理論中的應用將被詳盡介紹。我們將對特徵(Characteristic)進行精確定義和分類。 素理想與極大理想: 引入素理想(Prime Ideals)和極大理想(Maximal Ideals)的概念,它們是構建域和確定環結構的重要工具。通過分析這些理想,讀者將掌握如何從更基本的元素構造齣更復雜的結構。 第三部分:域論的幾何與代數連接 第三部分將聚焦於域(Fields)的理論,這是連接純代數與幾何、分析的關鍵領域,尤其在伽羅瓦理論(Galois Theory)的準備階段至關重要。 多項式環與因式分解: 在一個域上的多項式環(Polynomial Rings over a Field)是域論的核心研究對象。我們將詳細分析多項式的除法算法、最大公約式、以及不可約多項式的概念。對於單變量多項式環,我們將證明其具有唯一因式分解的性質(Unique Factorization Domains, UFDs)。 域的擴張: 域擴張(Field Extensions)是本部分的核心。定義瞭擴張域、次數(Degree of Extension)以及代數元(Algebraic Elements)和超越元(Transcendental Elements)。我們將深入研究擴域的構造,特彆是通過根(Roots)的添加來構造新的域。 分裂域與最小多項式: 最小多項式(Minimal Polynomial)的唯一性和重要性將被證明。在此基礎上,分裂域(Splitting Fields)的概念被引入,它為理解多項式根的結構提供瞭精確的框架。 結構性總結: 本書的最終目標是為讀者提供一個清晰的、相互關聯的代數框架。從群的對稱性到環的運算規律,再到域的擴張結構,這些理論共同構成瞭現代數學分析和建模的基石。全書配備瞭大量的例題和習題,旨在培養讀者獨立解決問題的能力和對抽象代數本質的深刻洞察力。