内容简介
The audacious title of this book deserves an explanation. Almost all linear algebra books use determinants to prove that every linear operator on a finite-dimensional complex vector space has an eigenvalue. Determinants are difficult, nonintuitive, and often defined without motivation. To prove the theorem about existence of eigenvalues on complex vector spaces, most books must.define determinants, prove that a linear map is not invertible ff and only if its determinant equals O, and then define the characteristic polynomial. This tortuous (torturous?) path gives students little feeling for why eigenvalues must exist. In contrast, the simple determinant-free proofs presented here offer more insight. Once determinants have been banished to the end of the book, a new route opens to the main goal of linear algebra-- understanding the structure of linear operators.
内页插图
目录
Preface to the Instructor
Preface to the Student
Acknowledgments
CHAPTER 1
Vector Spaces
Complex Numbers
Definition of Vector Space
Properties of Vector Spaces
Subspaces
Sums and Direct Sums
Exercises
CHAPTER 2
Finite-Dimenslonal Vector Spaces
Span and Linear Independence
Bases
Dimension
Exercises
CHAPTER 3
Linear Maps
Definitions and Examples
Null Spaces and Ranges
The Matrix of a Linear Map
Invertibility
Exercises
CHAPTER 4
Potynomiags
Degree
Complex Coefficients
Real Coefflcients
Exercises
CHAPTER 5
Eigenvalues and Eigenvectors
lnvariant Subspaces
Polynomials Applied to Operators
Upper-Triangular Matrices
Diagonal Matrices
Invariant Subspaces on Real Vector Spaces
Exercises
CHAPTER 6
Inner-Product spaces
Inner Products
Norms
Orthonormal Bases
Orthogonal Projections and Minimization Problems
Linear Functionals and Adjoints
Exercises
CHAPTER 7
Operators on Inner-Product Spaces
Self-Adjoint and Normal Operators
The Spectral Theorem
Normal Operators on Real Inner-Product Spaces
Positive Operators
Isometries
Polar and Singular-Value Decompositions
Exercises
CHAPTER 8
Operators on Complex Vector Spaces
Generalized Eigenvectors
The Characteristic Polynomial
Decomposition of an Operator
Square Roots
The Minimal Polynomial
Jordan Form
Exercises
CHAPTER 9
Operators on Real Vector Spaces
Eigenvalues of Square Matrices
Block Upper-Triangular Matrices
The Characteristic Polynomial
Exercises
CHAPTER 10
Trace and Determinant
Change of Basis
Trace
Determinant of an Operator
Determinant of a Matrix
Volume
Exercises
Symbol Index
Index
前言/序言
You are probably about to teach a course that will give students their second exposure to linear algebra. During their first brush with the subject, your students probably worked with Euclidean spaces and matrices. In contrast, this course will emphasize abstract vector spaces and linear maps.
The audacious title of this book deserves an explanation. Almost all linear algebra books use determinants to prove that every linear operator on a finite-dimensional complex vector space has an eigenvalue.Determinants are difficult, nonintuitive, and often defined without motivation. To prove the theorem about existence of eigenvalues on complex vector spaces, most books must define determinants, prove that a linear map is not invertible if and only ff its determinant equals O, and then define the characteristic polynomial. This tortuous (torturous?) path gives students little feeling for why eigenvalues must exist.
In contrast, the simple determinant-free proofs presented here offer more insight. Once determinants have been banished to the end of the book, a new route opens to the main goal of linear algebra-understanding the structure of linear operators.
This book starts at the beginning of the subject, with no prerequi-sites other than the usual demand for suitable mathematical maturity.Even if your students have already seen some of the material in the first few chapters, they may be unaccustomed to working exercises of the type presented here, most of which require an understanding of proofs.
Vector spaces are defined in Chapter 1, and their basic propertiesare developed.
线性代数(第2版)(英文影印版)[LINEAR ALGEBRA DONE RIGHT 2nd ed] 内容概述 本书聚焦于线性代数的现代观点,强调理论基础的严谨性和几何直观的培养,旨在为读者提供一个深入且连贯的代数结构理解。它避开了传统教材中过于依赖行列式和具体计算的叙述方式,转而从向量空间、线性映射和内在结构的角度展开。 第一部分:向量空间的基础 本书的开篇奠定了线性代数的核心概念——向量空间。它不仅仅将向量空间视为$mathbb{R}^n$或$mathbb{C}^n$的特例,而是将其抽象化为一个满足特定公理的集合。 向量空间的定义与例子: 详细阐述了向量加法和标量乘法的封闭性及运算性质。涵盖了经典的欧几里得空间、多项式空间、函数空间,以及更抽象的矩阵空间等多种实例,帮助读者理解抽象概念在不同数学领域中的体现。 子空间: 介绍了子空间的概念,并探讨了子空间的交集和和空间的性质。特别是对零空间(trivial subspace)的讨论,为后续理解线性映射的核奠定了基础。 线性组合、跨度和线性无关性: 这是构建基和维度的基石。本书对线性组合的生成能力(跨度)进行了深入分析,并严格定义了线性无关性的含义——即集合中任意向量都不能由其余向量线性表示。 基和维数: 在建立了线性无关性的基础上,本书清晰地展示了任何有限维向量空间都存在基,并且任何两组基都具有相同的元素个数,从而给出了维数(Dimension)这一核心概念的严格定义。通过同构的概念,说明了所有有限维实数向量空间($mathbb{R}^n$)在抽象结构上是等价的。 第二部分:线性映射与矩阵表示 在理解了向量空间的结构后,本书将重点转向连接这些空间的桥梁——线性映射(Linear Maps)。 线性映射的定义与性质: 严格定义了保持向量空间结构(加法和标量乘法)的函数。探讨了线性映射的核(Null Space,或Kernel)和像(Range,或Image)作为子空间的性质,以及秩-零化度定理(Rank-Nullity Theorem)的推导和应用,这是理解线性映射大小和满射性的关键工具。 基的选择与矩阵表示: 本部分解释了矩阵如何作为线性映射在特定基下的“坐标表示”。重点在于理解矩阵的元素是如何依赖于所选基的。如果基发生变化,矩阵如何通过相似变换(Similarity Transformation)进行关联,强调了矩阵是变换的表示而非变换本身。 同构与同态: 探讨了保持结构(同态)和结构完全一致(同构)的映射。这使得读者能够识别出在不同“外观”下本质相同的代数结构。 第三部分:多线性与内积空间 本书拓展了基础概念,引入了对几何和分析至关重要的结构。 多线性映射与张量(Tensors): 虽然内容聚焦于线性代数基础,但对于更高级的结构,本书会触及多线性概念的萌芽,特别是通过外积或对偶空间来理解更高阶的结构,为后续深入研究提供视角。 内积空间(Inner Product Spaces): 引入了内积这一额外的代数结构,它允许我们谈论长度、角度和正交性。详细讨论了内积的性质,并证明了柯西-施瓦茨不等式。 正交性与投影: 重点讨论了正交基和规范正交基的构建,特别是格拉姆-施密特正交化过程。通过正交投影定理,展示了如何在向量空间中找到“最佳逼近”的几何意义。 最小二乘法: 利用正交性原理,对线性方程组 $Ax=b$ 的最小二乘解进行了几何化和严谨的推导,这是本书应用性的一个亮点。 第四部分:特征值与对角化 本部分深入探讨了线性映射作用于向量时,哪些向量的方向保持不变,这是理解动力系统和微分方程解法的核心。 特征值与特征向量: 严格定义了 $lambda v = Tv$ 中的特征值和特征向量。 不变子空间: 引入了不变子空间的概念,它们是线性映射下保持自身结构的一类子空间。 对角化(Diagonalization): 阐述了何时一个线性映射(或矩阵)是可对角化的,即是否存在一组基使得该映射的矩阵表示成为对角矩阵。这极大地简化了对高次幂运算的理解。 不变式分解: 即使映射不可对角化,本书也会引入更一般的分解形式,如若当标准型(Jordan Canonical Form)的理论基础,通过将空间分解为特征子空间的直和来简化分析。 第五部分:结构与应用 本书在最后会关注那些不依赖于特定坐标表示的、内在的代数性质。 行列式(作为线性映射的固有属性): 行列式的介绍被后置,并被赋予了更深刻的几何意义——它代表了线性映射对体积(或面积)的缩放因子。本书更侧重于行列式的多线性函数性质,而非计算公式的推导。 二次型与对称性: 对于实内积空间,讨论了对称线性映射的性质,特别是谱定理(Spectral Theorem),它保证了实对称矩阵总是可以正交对角化的,这在物理和优化问题中至关重要。 本书的叙事风格清晰、逻辑严密,旨在培养读者对“为什么”而非仅仅“如何做”的深刻理解,从而为高等数学的进一步学习(如泛函分析、微分几何等)打下坚实的理论基础。