内容简介
This book provides an introduction to complex analysis for students with some familiarity with complex numbers from high school. Students should be familiar with the Cartesian representation of complex numbers and with the algebra of complex numbers, that is, they should know that i2 = -1. A familiarity with multivariable calculus is also required, but here the fundamental ideas are reviewed. In fact, complex analysis provides a good training ground for multivariable calculus. It allows students to consolidate their understanding of parametrized curves, tangent vectors, arc length, gradients, line integrals, independence of path, and Greens theorem. The ideas surrounding independence of path are particularly difficult for students in calculus, and they are not absorbed by most students until they are seen again in other courses.
内页插图
目录
Preface
Introduction
FIRST PART
Chapter 1 The Complex Plane and Elementary Functions
1.Complex Numbers
2.Polar Representation
3.Stereographic Projection
4.The Square and Square Root Functions
5.The Exponential Function
6.The Logarithm Function
7.Power Functions and Phase Factors
8.Trigonometric and Hyperbolic Functions
Chapter 2 Analytic Functions
1.Review of Basic Analysis
2.Analytic Functions
3.The CauChy-Riemann Equations
4.Inverse Mappings and the Jacobian
5.Harmonic Functions
6.Conformal Mappings
7.Fractional Linear Transformations
Chapter 3 Line Integrals and Harmonic Functions
1.Line Integrals and Greens Theorem
2.Independence of Path
3.Harmonic Conjugates
4.The Mean Value Property
5.The Maximum Principle
6.Applications to Fluid Dynamics
7.Other Applications to Physics
Chapter 4 Complex Integration and Analyticity
1.Complex Line Integrals
2.Fundamental Theorem of Calculus for Analytic Functions
3.Cauchys Theorem
4.The Cauchy Integral Formula
5.Liouvilles Theorem
6.Moreras Theorem
7.Goursats Theorem
8.Complex Notation and Pompeius Formula
Chapter 5 Power Series
1.Infinite Series
2.Sequences and Series of Functions
3.Power Series
4.Power Series Expansion of an Analytic Function
5.Power Series Expansion at Infinity
6.Manipulation of Power Series
7.The Zeros of an Analytic Function
8.Analytic Continuation
Chapter 6 Laurent Series and Isolated Singularities
1.The Laurent Decomposition
2.Isolated Singularities of an Analytic Function
3.Isolated Singularity at Infinity
4.Partial Fractions Decomposition
5.Periodic Functions
6.Fourier Series
Chapter 7 The Residue Calculus
1.The Residue Theorem
2.Integrals Featuring Rational Functions
3.Integrals of Trigonometric Functions
4.Integrands with Branch Points
5.Fractional Residues
6.Principal Values
7.Jordans Lemma
8.Exterior Domains
SECOND PART
Chapter 8 The Logarithmic Integral
1.The Argument Principle
2.Rouches Theorem
3.Hurwitzs Theorem
4.Open Mapping and Inverse Function Theorems
5.Critical Points
6.Winding Numbers
……
THIRD PART
Hints and Solutions for Selected Exercises
References
List of Symbols
Index
前言/序言
This book provides an introduction to complex analysis for students with some familiarity with complex numbers from high school. Students should be familiar with the Cartesian representation of complex numbers and with the algebra of complex numbers, that is, they should know that i2=-1. A familiarity with multivariable calculus is also required, but here the fundamental ideas are reviewed. In fact, complex analysis provides a good training ground for multivariable calculus.It allows students to consolidate their understanding of parametrized curves, tangent vectors, arc length,gradients, line integrals, independence of path, and Greens theorem. The ideas surrounding independence of path are particularly difficult for students in calculus, and they are not absorbed by most students until they are seen again in other courses.
The book consists of sixteen chapters, which are divided into three parts.The first part, Chapters I-VII, includes basic material covered in all undergraduate courses. With the exception of a few sections, this material is much the same as that covered in Cauchys lectures, except that the emphasis on viewing functions as mappings reflects Riemanns influence. The second part, Chapters VIII-XI, bridges the nineteenth and the twentieth centuries. About half this material would be covered in a typical undergraduate course, depending upon the taste and pace of the instructor. The material on the Poisson integral is of interest to electrical engineers, while the material on hyperbolic geometry is of interest to pure mathematicians and also to high school mathematics teachers. The third part, Chapters XII-XVI, consists of a careful selection of special topics that illustrate the scope and power of complex analysis methods. These topics include Julia sets and the Mandelbrot set, Dirichlet series and the prime number theorem, and the uniformization theorem for Riemann surfaces. The final five chapters serve also to complete the coverage of all background necessary for passing PhD qualifying exams in complex analysis.
纯粹的逻辑之美:一部探寻函数精妙世界的导览 引言:数学的广袤疆域与复变函数的独特魅力 在数学的浩瀚星空中,不同的分支以其独特的视角和工具,描绘着自然界和抽象世界的深刻规律。几何学以空间的结构引人入胜,代数学以结构的本质引人入胜,而分析学,则以极限和无穷的精妙联系,构筑起关于变化与连续性的宏伟殿堂。在分析学的众多领域中,复变函数论,或称复分析,无疑是最为典雅和富有创造力的分支之一。它将实数轴的线性限制扩展到复平面这一二维的广阔空间,从而揭示了许多在实数范围内难以察觉的深刻性质和强大的计算工具。 本书旨在提供一个全面而深入的介绍,带领读者领略复分析的精髓。我们不会止步于对复数基本概念的简单回顾,而是将重点放在如何利用复数的结构,构建一套功能强大、逻辑严谨的理论体系。我们的目标是培养读者不仅能够熟练运用复分析的工具,更能理解这些工具背后的深刻数学思想。 第一部分:复数域的拓扑与几何基础 复分析的基石在于对复数 $mathbb{C}$ 的深刻理解。在本部分,我们将从复数的代数定义出发,迅速过渡到其几何解释——高斯平面。 代数结构的延伸: 我们将详细探讨复数的代数运算,包括加法、乘法、除法的定义,以及共轭复数和模长(绝对值)的概念。模长不仅仅是一个数值,它定义了复平面上的距离,这是后续所有收敛性、连续性和可微性讨论的几何基础。 拓扑环境的建立: 复平面上的拓扑结构是分析学的灵魂。我们将严谨地定义开集、闭集、邻域的概念,并引入球形邻域和圆盘的概念。这些定义将直接支撑我们后续讨论函数的极限和连续性。我们将着重分析复序列的收敛性,特别是当序列在复平面上收敛时的几何直观。有界集和紧集的性质在复平面上的表现,将为我们理解函数在特定区域内的行为提供必要的工具。 区域与路径: 在复分析中,我们关注的不仅仅是单个点,而是函数在区域上的整体表现。因此,对连通区域、凸集、以及路径(曲线)的讨论至关重要。我们定义了分段可微曲线,并引入了积分路径的概念,为后续的复积分做好铺垫。 第二部分:解析函数——复分析的中心概念 解析函数(Analytic Functions),或称全纯函数(Holomorphic Functions),是复分析理论的核心。它们是那些在某开区域内复可微的函数。这个“复可微”的条件,看似比实数的可微性多了一个维度(要求沿所有方向的导数相等),却产生了无比强大的约束力。 复导数的定义与意义: 我们将严格定义复导数的极限形式,并论证其对路径依赖性的要求。一旦一个函数是复可微的,其性质将远超一般的实函数。 柯西-黎曼(Cauchy-Riemann, C-R)方程: 这是连接复函数 $f(z) = u(x, y) + i v(x, y)$ 的实部和虚部,并判别函数是否解析的关键工具。我们将详细推导 C-R 方程,并展示如何利用它们来快速判断一个给定函数是否具有解析性。C-R 方程的重要性在于,它将二维实函数的偏导数运算与复函数导数的单一定向性联系起来。 解析函数的性质: 解析函数具有惊人的光滑性。我们将证明,一个函数若在某区域解析,则它在该区域内无穷次可微。这是解析函数区别于一般实可微函数的最显著特征之一。我们还将引入共轭调和函数(Harmonic Functions)的概念,并展示解析函数的实部和虚部必然是调和函数。 第三部分:复积分与柯西定理的威力 复积分是复分析中最具实践价值和理论深度的部分之一。它不仅是理论推导的工具,更是解决物理和工程问题的利器。 复线积分的定义: 我们将建立复线积分的定义,并探讨积分路径的选择对积分值的影响。这里,积分路径的参数化和对复函数模长的估计是计算的基础。 柯西-古尔萨(Cauchy-Goursat)定理: 这是复分析中最根本、最具革命性的定理之一。我们将严格证明,在一个单连通区域内,解析函数的闭合回路积分恒为零。这个定理极大地简化了复积分的计算,并揭示了解析函数在区域上的全局一致性。 积分公式的衍生: 基于柯西定理,我们将推导出柯西积分公式。这个公式具有惊人的洞察力:它表明在一个区域内的任何一点函数的取值,完全由该点边界上的函数值所决定。我们将利用柯西积分公式来证明解析函数的高阶可微性,进一步巩固解析函数的“超光滑”特性。 第四部分:泰勒级数、幂级数与留数定理 在实分析中,泰勒级数是描述函数局部行为的强大工具。在复分析中,由于解析函数的性质,幂级数(Power Series)在复平面上具有更强的代表性。 幂级数与收敛半径: 我们将讨论复幂级数的收敛性,并确定其收敛域——一个以级数中心为圆心的圆盘。 洛朗(Laurent)级数与奇点分类: 并非所有在复平面上可研究的函数都是处处解析的。当函数在某点不可微时,我们称之为奇点。洛朗级数是解析函数在去心邻域内的推广表示法,它可以包含负幂次的项。我们将利用洛朗级数对奇点进行分类:可去奇点、极点和本质奇点,每种奇点都揭示了函数在局部行为的独特特征。 留数(Residue)的概念与计算: 留数是洛朗级数中系数 $a_{-1}$ 的值。这个看似微小的系数,却蕴含着巨大的计算能量。我们将展示如何直接从函数表达式计算留数,特别是对于极点的情况。 留数定理的辉煌应用: 留数定理是复分析中最强大的计算工具。它表明,一个在区域内除有限个奇点外都解析的函数,其闭合回路积分的值,仅依赖于其内部奇点的留数之和。我们将利用留数定理来计算大量在实分析中难以处理的定积分和无穷级数求和问题,展示其在解决实际问题中的无可匹敌的效率。 结语:通向更深层次数学的桥梁 复分析不仅仅是一门独立的学科,它更是连接数学各个领域的桥梁。它的概念和方法深刻地影响了微分方程、微分几何、拓扑学,乃至理论物理学(如量子场论和流体力学)。通过对解析函数的深入研究,我们不仅掌握了一套强大的计算技巧,更重要的是,我们领悟到一种看待数学结构更高级、更和谐的视角。本书力求在保持严格的数学论证的同时,激发读者对复平面上函数行为之美和逻辑之纯粹的欣赏。