An Improved Riemann Mapping Theorem and Complexity In
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Mathematics 412 Partial Differential Equations
Mathematics 412 Partial Differential Equations c S. A. Fulling Fall, 2005 The Wave Equation This introductory example will have three parts.* 1. I will show how a particular, simple partial differential equation (PDE) arises in a physical problem. 2. We’ll look at its solutions, which happen to be unusually easy to find in this case. 3. We’ll solve the equation again by separation of variables, the central theme of this course, and see how Fourier series arise. The wave equation in two variables (one space, one time) is ∂2u ∂2u = c2 , ∂t2 ∂x2 where c is a constant, which turns out to be the speed of the waves described by the equation. Most textbooks derive the wave equation for a vibrating string (e.g., Haber- man, Chap. 4). It arises in many other contexts — for example, light waves (the electromagnetic field). For variety, I shall look at the case of sound waves (motion in a gas). Sound waves Reference: Feynman Lectures in Physics, Vol. 1, Chap. 47. We assume that the gas moves back and forth in one dimension only (the x direction). If there is no sound, then each bit of gas is at rest at some place (x,y,z). There is a uniform equilibrium density ρ0 (mass per unit volume) and pressure P0 (force per unit area). Now suppose the gas moves; all gas in the layer at x moves the same distance, X(x), but gas in other layers move by different distances. More precisely, at each time t the layer originally at x is displaced to x + X(x,t). -
A Measure on the Harmonic Boundary of a Riemann Surface
A MEASURE ON THE HARMONIC BOUNDARY OF A RIEMANN SURFACE MITSURU NAKAI Introduction 1. In the usual theory of harmonic functions on a plane domain, the fact that the boundary of the domain is realized relative to the complex plane plays an essential role and supplies many powerful tools, for instance, the solution of Dirichlet problem. But in the theory of harmonic functions on a general domain, i.e. on a Riemann surface, the main difficulty arises from the lack of the "visual" boundary of the surface. Needless to say, in general we cannot expect to get the "relative" boundary with respect to some other larger surface. In view of this, we need some "abstract" compactification. It seems likely that we cannot expect to get the "universal" boundary which is appropriate for any harmonic functions since there exist many surfaces which do not admit some classes of harmonic functions as the classification theory shows. Hence we need many compactifications corresponding to what class of harmonic functions we are going to investigate. There are two typical compactifications, as Royden [10] pointed out, Martin's compactification and Royden's compactification. The former seems appropriate for the study of //"^-functions and the latter aims to be used for the study of HBD-ίunctions, which we are going to investigate in this paper. Λ similar investigation is carried out by Kuramochi in the direction of Martin. 2. Royden's compactification is first introduced by Royden and has been studied by Mori, Mori-Ota, Kusunoki-Mori and the present author. But these investigations seem to be restricted for ffi?D-functions. -
A Very Short Survey on Boundary Behavior of Harmonic Functions
A VERY SHORT SURVEY ON BOUNDARY BEHAVIOR OF HARMONIC FUNCTIONS BLACK Abstract. This short expository paper aims to use Dirichlet boundary value problem to elab- orate on some of the interactions between complex analysis, potential theory, and harmonic analysis. In particular, I will outline Wiener's solution to the Dirichlet problem for a general planar domain using harmonic measure and prove some elementary results for Hardy spaces. 1. Introduction Definition 1.1. Let Ω Ă R2 be an open set. A function u P C2pΩ; Rq is called harmonic if B2u B2u (1.1) ∆u “ ` “ 0 on Ω: Bx2 By2 The notion of harmonic function can be generalized to any finite dimensional Euclidean space (or on (pseudo)Riemannian manifold), but the theory enjoys a qualitative difference in the planar case due to its relation to the magic properties of functions of one complex variable. Think of Ω Ă C (in this paper I will use R2 and C interchangeably when there is no confusion). Then the Laplace operator takes the form B B B 1 B B B 1 B B (1.2) ∆ “ 4 ; where “ ´ i and “ ` i : Bz¯ Bz Bz 2 Bx By Bz¯ 2 Bx By ˆ ˙ ˆ ˙ Let HolpΩq denote the space of holomorphic functions on Ω. It is easy to see that if f P HolpΩq, then both <f and =f are harmonic functions. Conversely, if u is harmonic on Ω and Ω is simply connected, we can construct a harmonic functionu ~, called the harmonic conjugate of u, via Hilbert transform (or more generally, B¨acklund transform), such that f “ u ` iu~ P HolpΩq. -
THE S.V.D. of the POISSON KERNEL 1. Introduction This Paper
THE S.V.D. OF THE POISSON KERNEL GILES AUCHMUTY Abstract. The solution of the Dirichlet problem for the Laplacian on bounded regions N Ω in R , N 2 is generally described via a boundary integral operator with the Poisson kernel. Under≥ mild regularity conditions on the boundary, this operator is a compact 2 2 2 linear transformation of L (∂Ω,dσ) to LH (Ω) - the Bergman space of L harmonic functions on Ω. This paper describes the singular value decomposition (SVD)− of this operator and related results. The singular functions and singular values are constructed using Steklov eigenvalues and eigenfunctions of the biharmonic operator on Ω. These allow a spectral representation of the Bergman harmonic projection and the identification 2 of an orthonormal basis of the real harmonic Bergman space LH (Ω). A reproducing 2 2 kernel for LH (Ω) and an orthonormal basis of the space L (∂Ω,dσ) also are found. This enables the description of optimal finite rank approximations of the Poisson kernel with error estimates. Explicit spectral formulae for the normal derivatives of eigenfunctions for the Dirichlet Laplacian on ∂Ω are obtained and used to identify a constant in an inequality of Hassell and Tao. 1. Introduction This paper describes representation results for harmonic functions on a bounded region Ω in RN ; N 2. In particular a spectral representation of the Poisson kernel for solutions of the Dirichlet≥ problem for Laplace’s equation with L2 boundary data is described. This leads to an explicit description of the Reproducing− Kernel (RK) for 2 the harmonic Bergman space LH (Ω) and the singular value decomposition (SVD) of the Poisson kernel for the Laplacian. -
Genius Manual I
Genius Manual i Genius Manual Genius Manual ii Copyright © 1997-2016 Jiríˇ (George) Lebl Copyright © 2004 Kai Willadsen Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License (GFDL), Version 1.1 or any later version published by the Free Software Foundation with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. You can find a copy of the GFDL at this link or in the file COPYING-DOCS distributed with this manual. This manual is part of a collection of GNOME manuals distributed under the GFDL. If you want to distribute this manual separately from the collection, you can do so by adding a copy of the license to the manual, as described in section 6 of the license. Many of the names used by companies to distinguish their products and services are claimed as trademarks. Where those names appear in any GNOME documentation, and the members of the GNOME Documentation Project are made aware of those trademarks, then the names are in capital letters or initial capital letters. DOCUMENT AND MODIFIED VERSIONS OF THE DOCUMENT ARE PROVIDED UNDER THE TERMS OF THE GNU FREE DOCUMENTATION LICENSE WITH THE FURTHER UNDERSTANDING THAT: 1. DOCUMENT IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, WITHOUT LIMITATION, WARRANTIES THAT THE DOCUMENT OR MODIFIED VERSION OF THE DOCUMENT IS FREE OF DEFECTS MERCHANTABLE, FIT FOR A PARTICULAR PURPOSE OR NON-INFRINGING. THE ENTIRE RISK AS TO THE QUALITY, ACCURACY, AND PERFORMANCE OF THE DOCUMENT OR MODIFIED VERSION OF THE DOCUMENT IS WITH YOU. -
Harmonic Measure
Chapter 6 Harmonic Measure Prologue: It is unfortunate that most graduate com- plex analysis courses do not treat harmonic measure. Indeed, most complex analysis texts do not cover the topic. The term “harmonic measure” was introduced by R. Nevanlinna in the 1920s. But the ideas were antici- pated in work of the Riesz brothers and others. It is still studied intensively today. Harmonic measure is a natural outgrowth of the study of the Dirichlet problem. It is a decisive tool for mea- suring the growth of functions, and to seeing how they bend. It has been used in such diverse applications as the corona problem and in mapping problems. Harmonic measure has particularly interesting applications in prob- ability theory—especially in the consideration of diffus- tions and Brownian motion. It requires a little sophistication to appreciate har- monic measure. And calculating the measure—working through the examples—requires some elbow grease. But the effort is worth it and the results are substantial. This chapter gives a basic introduction to the idea of harmonic measure. 169 79344-3_Printer Proof.pdf 183 “CH06” — 2015/10/26 — 17:20 — page 169 — #1 11/6/2015 1:52:49 PM 170 CHAPTER 6. HARMONIC MEASURE 6.1 The Idea of Harmonic Measure Capsule: Harmonic measure is a way of manipulating the data that comes from the Dirichlet problem. It is a way of measuring the geom- etry of a domain, and can be used to control the growth of harmonic functions. Let Ω ⊆ C be a domain with boundary consisting of finitely many Jordan curves (we call such a domain a Jordan domain). -
Convergence of Complete Ricci-Flat Manifolds Jiewon Park
Convergence of Complete Ricci-flat Manifolds by Jiewon Park Submitted to the Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mathematics at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY May 2020 © Massachusetts Institute of Technology 2020. All rights reserved. Author . Department of Mathematics April 17, 2020 Certified by. Tobias Holck Colding Cecil and Ida Green Distinguished Professor Thesis Supervisor Accepted by . Wei Zhang Chairman, Department Committee on Graduate Theses 2 Convergence of Complete Ricci-flat Manifolds by Jiewon Park Submitted to the Department of Mathematics on April 17, 2020, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mathematics Abstract This thesis is focused on the convergence at infinity of complete Ricci flat manifolds. In the first part of this thesis, we will give a natural way to identify between two scales, potentially arbitrarily far apart, in the case when a tangent cone at infinity has smooth cross section. The identification map is given as the gradient flow of a solution to an elliptic equation. We use an estimate of Colding-Minicozzi of a functional that measures the distance to the tangent cone. In the second part of this thesis, we prove a matrix Harnack inequality for the Laplace equation on manifolds with suitable curvature and volume growth assumptions, which is a pointwise estimate for the integrand of the aforementioned functional. This result provides an elliptic analogue of matrix Harnack inequalities for the heat equation or geometric flows. Thesis Supervisor: Tobias Holck Colding Title: Cecil and Ida Green Distinguished Professor 3 4 Acknowledgments First and foremost I would like to thank my advisor Tobias Colding for his continuous guidance and encouragement, and for suggesting problems to work on. -
Elementary Applications of Fourier Analysis
ELEMENTARY APPLICATIONS OF FOURIER ANALYSIS COURTOIS Abstract. This paper is intended as a brief introduction to one of the very first applications of Fourier analysis: the study of heat conduction. We derive the steady state equation, which serves as our motivating PDE, and then iden- tify solutions to two fundamental scenarios: the first, a heat distribution on a circle; the second, one on a rod. In doing all of this there is much more room for depth that simply isn't explored for brevity's sake. A more comprehensive paper could explicitly define what constitutes a good kernel, the limitations of convergence of the Fourier transform, and different ways to circumvent these limitations. Theoretically, there's room to explore harmonic functions explic- itly, as well as Hilbert spaces and the L2 space. That would be the more analytic route to take; on the other hand there are many fascinating applica- tions that aren't broached either. In math, application is nearly synonymous with PDEs, and as far as partial differential equations are concerned, the most important feature that the Fourier transform has is the property of exchanging differentiation for multiplication. This property is really what makes bothering with the Fourier transforms of most functions worth it at all. Another equally important property of Fourier transforms is called scaling, which, in physics, directly leads to a concept called the Heisenberg Uncertainty Principle, which, like the whole of quantum physics, is very good at bothering people. Contents 1. Introduction 1 2. The heat equation 2 3. The Steady-state equation and the Laplacian 3 4. -
Topics on Calculus of Variations
TOPICS ON CALCULUS OF VARIATIONS AUGUSTO C. PONCE ABSTRACT. Lecture notes presented in the School on Nonlinear Differential Equa- tions (October 9–27, 2006) at ICTP, Trieste, Italy. CONTENTS 1. The Laplace equation 1 1.1. The Dirichlet Principle 2 1.2. The dawn of the Direct Methods 4 1.3. The modern formulation of the Calculus of Variations 4 1 1.4. The space H0 (Ω) 4 1.5. The weak formulation of (1.2) 8 1.6. Weyl’s lemma 9 2. The Poisson equation 11 2.1. The Newtonian potential 11 2.2. Solving (2.1) 12 3. The eigenvalue problem 13 3.1. Existence step 13 3.2. Regularity step 15 3.3. Proof of Theorem 3.1 16 4. Semilinear elliptic equations 16 4.1. Existence step 17 4.2. Regularity step 18 4.3. Proof of Theorem 4.1 20 References 20 1. THE LAPLACE EQUATION Let Ω ⊂ RN be a body made of some uniform material; on the boundary of Ω, we prescribe some fixed temperature f. Consider the following Question. What is the equilibrium temperature inside Ω? Date: August 29, 2008. 1 2 AUGUSTO C. PONCE Mathematically, if u denotes the temperature in Ω, then we want to solve the equation ∆u = 0 in Ω, (1.1) u = f on ∂Ω. We shall always assume that f : ∂Ω → R is a given smooth function and Ω ⊂ RN , N ≥ 3, is a smooth, bounded, connected open set. We say that u is a classical solution of (1.1) if u ∈ C2(Ω) and u satisfies (1.1) at every point of Ω. -
Uniformization of Riemann Surfaces
CHAPTER 3 Uniformization of Riemann surfaces 3.1 The Dirichlet Problem on Riemann surfaces 128 3.2 Uniformization of simply connected Riemann surfaces 141 3.3 Uniformization of Riemann surfaces and Kleinian groups 148 3.4 Hyperbolic Geometry, Fuchsian Groups and Hurwitz’s Theorem 162 3.5 Moduli of Riemann surfaces 178 127 128 3. UNIFORMIZATION OF RIEMANN SURFACES One of the most important results in the area of Riemann surfaces is the Uni- formization theorem, which classifies all simply connected surfaces up to biholomor- phisms. In this chapter, after a technical section on the Dirichlet problem (solutions of equations involving the Laplacian operator), we prove that theorem. It turns out that there are very few simply connected surfaces: the Riemann sphere, the complex plane and the unit disc. We use this result in 3.2 to give a general formulation of the Uniformization theorem and obtain some consequences, like the classification of all surfaces with abelian fundamental group. We will see that most surfaces have the unit disc as their universal covering space, these surfaces are the object of our study in 3.3 and 3.5; we cover some basic properties of the Riemaniann geometry, §§ automorphisms, Kleinian groups and the problem of moduli. 3.1. The Dirichlet Problem on Riemann surfaces In this section we recall some result from Complex Analysis that some readers might not be familiar with. More precisely, we solve the Dirichlet problem; that is, to find a harmonic function on a domain with given boundary values. This will be used in the next section when we classify all simply connected Riemann surfaces. -
THE IMPACT of RIEMANN's MAPPING THEOREM in the World
THE IMPACT OF RIEMANN'S MAPPING THEOREM GRANT OWEN In the world of mathematics, scholars and academics have long sought to understand the work of Bernhard Riemann. Born in a humble Ger- man home, Riemann became one of the great mathematical minds of the 19th century. Evidence of his genius is reflected in the greater mathematical community by their naming 72 different mathematical terms after him. His contributions range from mathematical topics such as trigonometric series, birational geometry of algebraic curves, and differential equations to fields in physics and philosophy [3]. One of his contributions to mathematics, the Riemann Mapping Theorem, is among his most famous and widely studied theorems. This theorem played a role in the advancement of several other topics, including Rie- mann surfaces, topology, and geometry. As a result of its widespread application, it is worth studying not only the theorem itself, but how Riemann derived it and its impact on the work of mathematicians since its publication in 1851 [3]. Before we begin to discover how he derived his famous mapping the- orem, it is important to understand how Riemann's upbringing and education prepared him to make such a contribution in the world of mathematics. Prior to enrolling in university, Riemann was educated at home by his father and a tutor before enrolling in high school. While in school, Riemann did well in all subjects, which strengthened his knowl- edge of philosophy later in life, but was exceptional in mathematics. He enrolled at the University of G¨ottingen,where he learned from some of the best mathematicians in the world at that time. -
Lectures on Partial Differential Equations
Lectures on Partial Differential Equations Govind Menon1 Dec. 2005 Abstract These are my incomplete lecture notes for the graduate introduction to PDE at Brown University in Fall 2005. The lectures on Laplace’s equation and the heat equation are included here. Typing took too much work after that. I hope what is here is still useful. Andreas Kl¨ockner’s transcript of the remaining lectures is also posted on my website. Those however have not been proofread. Comments are wel- come by email. Contents 1 Laplace’s equation 3 1.1 Introduction............................ 3 1.1.1 Minimal surfaces and Laplace’s equation . 3 1.1.2 Fields and Laplace’s equation . 5 1.1.3 Motivation v. Results . 5 1.2 Notation.............................. 5 1.3 Themeanvalueinequality. 6 1.4 Maximumprinciples ....................... 8 1.5 Thefundamentalsolution . 10 1.6 Green’s function and Poisson’s integral formula . 13 1.7 The mean value property revisited . 17 1.8 Harmonic functions are analytic . 17 1.9 Compactness and convergence . 21 1.10 Perron’s method for the Dirichlet problem . 22 1.11 Energy methods and Dirichlet’s principle . 26 1.12 Potentials of measures . 28 1.13 Lebesgue’sthorn .. .. .. .. .. .. .. 30 1.14 The potential of a compact set . 33 1.15 Capacity of compact sets . 37 1 2 1.16 Variational principles for capacity . 39 2 The heat equation 43 2.1 Motivation ............................ 43 2.2 Thefundamentalsolution . 43 2.3 Uniquenessofsolutions . 47 2.4 Theweakmaximumprinciple . 48 2.5 Themeanvalueproperty . 49 2.6 Thestrongmaximumprinciple . 53 2.7 Differenceschemes . .. .. .. .. .. .. 54 2.8 Randomwalks .......................... 56 2.9 Brownianmotion ........................