內容簡介
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.
內頁插圖
目錄
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.
純粹的邏輯之美:一部探尋函數精妙世界的導覽 引言:數學的廣袤疆域與復變函數的獨特魅力 在數學的浩瀚星空中,不同的分支以其獨特的視角和工具,描繪著自然界和抽象世界的深刻規律。幾何學以空間的結構引人入勝,代數學以結構的本質引人入勝,而分析學,則以極限和無窮的精妙聯係,構築起關於變化與連續性的宏偉殿堂。在分析學的眾多領域中,復變函數論,或稱復分析,無疑是最為典雅和富有創造力的分支之一。它將實數軸的綫性限製擴展到復平麵這一二維的廣闊空間,從而揭示瞭許多在實數範圍內難以察覺的深刻性質和強大的計算工具。 本書旨在提供一個全麵而深入的介紹,帶領讀者領略復分析的精髓。我們不會止步於對復數基本概念的簡單迴顧,而是將重點放在如何利用復數的結構,構建一套功能強大、邏輯嚴謹的理論體係。我們的目標是培養讀者不僅能夠熟練運用復分析的工具,更能理解這些工具背後的深刻數學思想。 第一部分:復數域的拓撲與幾何基礎 復分析的基石在於對復數 $mathbb{C}$ 的深刻理解。在本部分,我們將從復數的代數定義齣發,迅速過渡到其幾何解釋——高斯平麵。 代數結構的延伸: 我們將詳細探討復數的代數運算,包括加法、乘法、除法的定義,以及共軛復數和模長(絕對值)的概念。模長不僅僅是一個數值,它定義瞭復平麵上的距離,這是後續所有收斂性、連續性和可微性討論的幾何基礎。 拓撲環境的建立: 復平麵上的拓撲結構是分析學的靈魂。我們將嚴謹地定義開集、閉集、鄰域的概念,並引入球形鄰域和圓盤的概念。這些定義將直接支撐我們後續討論函數的極限和連續性。我們將著重分析復序列的收斂性,特彆是當序列在復平麵上收斂時的幾何直觀。有界集和緊集的性質在復平麵上的錶現,將為我們理解函數在特定區域內的行為提供必要的工具。 區域與路徑: 在復分析中,我們關注的不僅僅是單個點,而是函數在區域上的整體錶現。因此,對連通區域、凸集、以及路徑(麯綫)的討論至關重要。我們定義瞭分段可微麯綫,並引入瞭積分路徑的概念,為後續的復積分做好鋪墊。 第二部分:解析函數——復分析的中心概念 解析函數(Analytic Functions),或稱全純函數(Holomorphic Functions),是復分析理論的核心。它們是那些在某開區域內復可微的函數。這個“復可微”的條件,看似比實數的可微性多瞭一個維度(要求沿所有方嚮的導數相等),卻産生瞭無比強大的約束力。 復導數的定義與意義: 我們將嚴格定義復導數的極限形式,並論證其對路徑依賴性的要求。一旦一個函數是復可微的,其性質將遠超一般的實函數。 柯西-黎曼(Cauchy-Riemann, C-R)方程: 這是連接復函數 $f(z) = u(x, y) + i v(x, y)$ 的實部和虛部,並判彆函數是否解析的關鍵工具。我們將詳細推導 C-R 方程,並展示如何利用它們來快速判斷一個給定函數是否具有解析性。C-R 方程的重要性在於,它將二維實函數的偏導數運算與復函數導數的單一定嚮性聯係起來。 解析函數的性質: 解析函數具有驚人的光滑性。我們將證明,一個函數若在某區域解析,則它在該區域內無窮次可微。這是解析函數區彆於一般實可微函數的最顯著特徵之一。我們還將引入共軛調和函數(Harmonic Functions)的概念,並展示解析函數的實部和虛部必然是調和函數。 第三部分:復積分與柯西定理的威力 復積分是復分析中最具實踐價值和理論深度的部分之一。它不僅是理論推導的工具,更是解決物理和工程問題的利器。 復綫積分的定義: 我們將建立復綫積分的定義,並探討積分路徑的選擇對積分值的影響。這裏,積分路徑的參數化和對復函數模長的估計是計算的基礎。 柯西-古爾薩(Cauchy-Goursat)定理: 這是復分析中最根本、最具革命性的定理之一。我們將嚴格證明,在一個單連通區域內,解析函數的閉閤迴路積分恒為零。這個定理極大地簡化瞭復積分的計算,並揭示瞭解析函數在區域上的全局一緻性。 積分公式的衍生: 基於柯西定理,我們將推導齣柯西積分公式。這個公式具有驚人的洞察力:它錶明在一個區域內的任何一點函數的取值,完全由該點邊界上的函數值所決定。我們將利用柯西積分公式來證明解析函數的高階可微性,進一步鞏固解析函數的“超光滑”特性。 第四部分:泰勒級數、冪級數與留數定理 在實分析中,泰勒級數是描述函數局部行為的強大工具。在復分析中,由於解析函數的性質,冪級數(Power Series)在復平麵上具有更強的代錶性。 冪級數與收斂半徑: 我們將討論復冪級數的收斂性,並確定其收斂域——一個以級數中心為圓心的圓盤。 洛朗(Laurent)級數與奇點分類: 並非所有在復平麵上可研究的函數都是處處解析的。當函數在某點不可微時,我們稱之為奇點。洛朗級數是解析函數在去心鄰域內的推廣錶示法,它可以包含負冪次的項。我們將利用洛朗級數對奇點進行分類:可去奇點、極點和本質奇點,每種奇點都揭示瞭函數在局部行為的獨特特徵。 留數(Residue)的概念與計算: 留數是洛朗級數中係數 $a_{-1}$ 的值。這個看似微小的係數,卻蘊含著巨大的計算能量。我們將展示如何直接從函數錶達式計算留數,特彆是對於極點的情況。 留數定理的輝煌應用: 留數定理是復分析中最強大的計算工具。它錶明,一個在區域內除有限個奇點外都解析的函數,其閉閤迴路積分的值,僅依賴於其內部奇點的留數之和。我們將利用留數定理來計算大量在實分析中難以處理的定積分和無窮級數求和問題,展示其在解決實際問題中的無可匹敵的效率。 結語:通嚮更深層次數學的橋梁 復分析不僅僅是一門獨立的學科,它更是連接數學各個領域的橋梁。它的概念和方法深刻地影響瞭微分方程、微分幾何、拓撲學,乃至理論物理學(如量子場論和流體力學)。通過對解析函數的深入研究,我們不僅掌握瞭一套強大的計算技巧,更重要的是,我們領悟到一種看待數學結構更高級、更和諧的視角。本書力求在保持嚴格的數學論證的同時,激發讀者對復平麵上函數行為之美和邏輯之純粹的欣賞。