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Arxiv:1006.1489V2 [Math.GT] 8 Aug 2010 Ril.Ias Rfie Rmraigtesre Rils[14 Articles Survey the Reading from Profited Also I Article
Pure and Applied Mathematics Quarterly Volume 8, Number 1 (Special Issue: In honor of F. Thomas Farrell and Lowell E. Jones, Part 1 of 2 ) 1—14, 2012 The Work of Tom Farrell and Lowell Jones in Topology and Geometry James F. Davis∗ Tom Farrell and Lowell Jones caused a paradigm shift in high-dimensional topology, away from the view that high-dimensional topology was, at its core, an algebraic subject, to the current view that geometry, dynamics, and analysis, as well as algebra, are key for classifying manifolds whose fundamental group is infinite. Their collaboration produced about fifty papers over a twenty-five year period. In this tribute for the special issue of Pure and Applied Mathematics Quarterly in their honor, I will survey some of the impact of their joint work and mention briefly their individual contributions – they have written about one hundred non-joint papers. 1 Setting the stage arXiv:1006.1489v2 [math.GT] 8 Aug 2010 In order to indicate the Farrell–Jones shift, it is necessary to describe the situation before the onset of their collaboration. This is intimidating – during the period of twenty-five years starting in the early fifties, manifold theory was perhaps the most active and dynamic area of mathematics. Any narrative will have omissions and be non-linear. Manifold theory deals with the classification of ∗I thank Shmuel Weinberger and Tom Farrell for their helpful comments on a draft of this article. I also profited from reading the survey articles [14] and [4]. 2 James F. Davis manifolds. There is an existence question – when is there a closed manifold within a particular homotopy type, and a uniqueness question, what is the classification of manifolds within a homotopy type? The fifties were the foundational decade of manifold theory. -
The General Linear Group
18.704 Gabe Cunningham 2/18/05 [email protected] The General Linear Group Definition: Let F be a field. Then the general linear group GLn(F ) is the group of invert- ible n × n matrices with entries in F under matrix multiplication. It is easy to see that GLn(F ) is, in fact, a group: matrix multiplication is associative; the identity element is In, the n × n matrix with 1’s along the main diagonal and 0’s everywhere else; and the matrices are invertible by choice. It’s not immediately clear whether GLn(F ) has infinitely many elements when F does. However, such is the case. Let a ∈ F , a 6= 0. −1 Then a · In is an invertible n × n matrix with inverse a · In. In fact, the set of all such × matrices forms a subgroup of GLn(F ) that is isomorphic to F = F \{0}. It is clear that if F is a finite field, then GLn(F ) has only finitely many elements. An interesting question to ask is how many elements it has. Before addressing that question fully, let’s look at some examples. ∼ × Example 1: Let n = 1. Then GLn(Fq) = Fq , which has q − 1 elements. a b Example 2: Let n = 2; let M = ( c d ). Then for M to be invertible, it is necessary and sufficient that ad 6= bc. If a, b, c, and d are all nonzero, then we can fix a, b, and c arbitrarily, and d can be anything but a−1bc. This gives us (q − 1)3(q − 2) matrices. -
Unitary Group - Wikipedia
Unitary group - Wikipedia https://en.wikipedia.org/wiki/Unitary_group Unitary group In mathematics, the unitary group of degree n, denoted U( n), is the group of n × n unitary matrices, with the group operation of matrix multiplication. The unitary group is a subgroup of the general linear group GL( n, C). Hyperorthogonal group is an archaic name for the unitary group, especially over finite fields. For the group of unitary matrices with determinant 1, see Special unitary group. In the simple case n = 1, the group U(1) corresponds to the circle group, consisting of all complex numbers with absolute value 1 under multiplication. All the unitary groups contain copies of this group. The unitary group U( n) is a real Lie group of dimension n2. The Lie algebra of U( n) consists of n × n skew-Hermitian matrices, with the Lie bracket given by the commutator. The general unitary group (also called the group of unitary similitudes ) consists of all matrices A such that A∗A is a nonzero multiple of the identity matrix, and is just the product of the unitary group with the group of all positive multiples of the identity matrix. Contents Properties Topology Related groups 2-out-of-3 property Special unitary and projective unitary groups G-structure: almost Hermitian Generalizations Indefinite forms Finite fields Degree-2 separable algebras Algebraic groups Unitary group of a quadratic module Polynomial invariants Classifying space See also Notes References Properties Since the determinant of a unitary matrix is a complex number with norm 1, the determinant gives a group 1 of 7 2/23/2018, 10:13 AM Unitary group - Wikipedia https://en.wikipedia.org/wiki/Unitary_group homomorphism The kernel of this homomorphism is the set of unitary matrices with determinant 1. -
An Overview of Topological Groups: Yesterday, Today, Tomorrow
axioms Editorial An Overview of Topological Groups: Yesterday, Today, Tomorrow Sidney A. Morris 1,2 1 Faculty of Science and Technology, Federation University Australia, Victoria 3353, Australia; [email protected]; Tel.: +61-41-7771178 2 Department of Mathematics and Statistics, La Trobe University, Bundoora, Victoria 3086, Australia Academic Editor: Humberto Bustince Received: 18 April 2016; Accepted: 20 April 2016; Published: 5 May 2016 It was in 1969 that I began my graduate studies on topological group theory and I often dived into one of the following five books. My favourite book “Abstract Harmonic Analysis” [1] by Ed Hewitt and Ken Ross contains both a proof of the Pontryagin-van Kampen Duality Theorem for locally compact abelian groups and the structure theory of locally compact abelian groups. Walter Rudin’s book “Fourier Analysis on Groups” [2] includes an elegant proof of the Pontryagin-van Kampen Duality Theorem. Much gentler than these is “Introduction to Topological Groups” [3] by Taqdir Husain which has an introduction to topological group theory, Haar measure, the Peter-Weyl Theorem and Duality Theory. Of course the book “Topological Groups” [4] by Lev Semyonovich Pontryagin himself was a tour de force for its time. P. S. Aleksandrov, V.G. Boltyanskii, R.V. Gamkrelidze and E.F. Mishchenko described this book in glowing terms: “This book belongs to that rare category of mathematical works that can truly be called classical - books which retain their significance for decades and exert a formative influence on the scientific outlook of whole generations of mathematicians”. The final book I mention from my graduate studies days is “Topological Transformation Groups” [5] by Deane Montgomery and Leo Zippin which contains a solution of Hilbert’s fifth problem as well as a structure theory for locally compact non-abelian groups. -
GROUP ACTIONS 1. Introduction the Groups Sn, An, and (For N ≥ 3)
GROUP ACTIONS KEITH CONRAD 1. Introduction The groups Sn, An, and (for n ≥ 3) Dn behave, by their definitions, as permutations on certain sets. The groups Sn and An both permute the set f1; 2; : : : ; ng and Dn can be considered as a group of permutations of a regular n-gon, or even just of its n vertices, since rigid motions of the vertices determine where the rest of the n-gon goes. If we label the vertices of the n-gon in a definite manner by the numbers from 1 to n then we can view Dn as a subgroup of Sn. For instance, the labeling of the square below lets us regard the 90 degree counterclockwise rotation r in D4 as (1234) and the reflection s across the horizontal line bisecting the square as (24). The rest of the elements of D4, as permutations of the vertices, are in the table below the square. 2 3 1 4 1 r r2 r3 s rs r2s r3s (1) (1234) (13)(24) (1432) (24) (12)(34) (13) (14)(23) If we label the vertices in a different way (e.g., swap the labels 1 and 2), we turn the elements of D4 into a different subgroup of S4. More abstractly, if we are given a set X (not necessarily the set of vertices of a square), then the set Sym(X) of all permutations of X is a group under composition, and the subgroup Alt(X) of even permutations of X is a group under composition. If we list the elements of X in a definite order, say as X = fx1; : : : ; xng, then we can think about Sym(X) as Sn and Alt(X) as An, but a listing in a different order leads to different identifications 1 of Sym(X) with Sn and Alt(X) with An. -
Mathematics of the Rubik's Cube
Mathematics of the Rubik's cube Associate Professor W. D. Joyner Spring Semester, 1996{7 2 \By and large it is uniformly true that in mathematics that there is a time lapse between a mathematical discovery and the moment it becomes useful; and that this lapse can be anything from 30 to 100 years, in some cases even more; and that the whole system seems to function without any direction, without any reference to usefulness, and without any desire to do things which are useful." John von Neumann COLLECTED WORKS, VI, p. 489 For more mathematical quotes, see the first page of each chapter below, [M], [S] or the www page at http://math.furman.edu/~mwoodard/mquot. html 3 \There are some things which cannot be learned quickly, and time, which is all we have, must be paid heavily for their acquiring. They are the very simplest things, and because it takes a man's life to know them the little new that each man gets from life is very costly and the only heritage he has to leave." Ernest Hemingway (From A. E. Hotchner, PAPA HEMMINGWAY, Random House, NY, 1966) 4 Contents 0 Introduction 13 1 Logic and sets 15 1.1 Logic................................ 15 1.1.1 Expressing an everyday sentence symbolically..... 18 1.2 Sets................................ 19 2 Functions, matrices, relations and counting 23 2.1 Functions............................. 23 2.2 Functions on vectors....................... 28 2.2.1 History........................... 28 2.2.2 3 × 3 matrices....................... 29 2.2.3 Matrix multiplication, inverses.............. 30 2.2.4 Muliplication and inverses............... -
Lie Group and Geometry on the Lie Group SL2(R)
INDIAN INSTITUTE OF TECHNOLOGY KHARAGPUR Lie group and Geometry on the Lie Group SL2(R) PROJECT REPORT – SEMESTER IV MOUSUMI MALICK 2-YEARS MSc(2011-2012) Guided by –Prof.DEBAPRIYA BISWAS Lie group and Geometry on the Lie Group SL2(R) CERTIFICATE This is to certify that the project entitled “Lie group and Geometry on the Lie group SL2(R)” being submitted by Mousumi Malick Roll no.-10MA40017, Department of Mathematics is a survey of some beautiful results in Lie groups and its geometry and this has been carried out under my supervision. Dr. Debapriya Biswas Department of Mathematics Date- Indian Institute of Technology Khargpur 1 Lie group and Geometry on the Lie Group SL2(R) ACKNOWLEDGEMENT I wish to express my gratitude to Dr. Debapriya Biswas for her help and guidance in preparing this project. Thanks are also due to the other professor of this department for their constant encouragement. Date- place-IIT Kharagpur Mousumi Malick 2 Lie group and Geometry on the Lie Group SL2(R) CONTENTS 1.Introduction ................................................................................................... 4 2.Definition of general linear group: ............................................................... 5 3.Definition of a general Lie group:................................................................... 5 4.Definition of group action: ............................................................................. 5 5. Definition of orbit under a group action: ...................................................... 5 6.1.The general linear -
Bott Periodicity for the Unitary Group
Bott Periodicity for the Unitary Group Carlos Salinas March 7, 2018 Abstract We will present a condensed proof of the Bott Periodicity Theorem for the unitary group U following John Milnor’s classic Morse Theory. There are many documents on the internet which already purport to do this (and do so very well in my estimation), but I nevertheless will attempt to give a summary of the result. Contents 1 The Basics 2 2 Fiber Bundles 3 2.1 First fiber bundle . .4 2.2 Second Fiber Bundle . .5 2.3 Third Fiber Bundle . .5 2.4 Fourth Fiber Bundle . .5 3 Proof of the Periodicity Theorem 6 3.1 The first equivalence . .7 3.2 The second equality . .8 4 The Homotopy Groups of U 8 1 The Basics The original proof of the Periodicity Theorem relies on a deep result of Marston Morse’s calculus of variations, the (Morse) Index Theorem. The proof of this theorem, however, goes beyond the scope of this document, the reader is welcome to read the relevant section from Milnor or indeed Morse’s own paper titled The Index Theorem in the Calculus of Variations. Perhaps the first thing we should set about doing is introducing the main character of our story; this will be the unitary group. The unitary group of degree n (here denoted U(n)) is the set of all unitary matrices; that is, the set of all A ∈ GL(n, C) such that AA∗ = I where A∗ is the conjugate of the transpose of A (conjugate transpose for short). -
An Algebraic Approach to the Weyl Groupoid
An Algebraic Approach to the Weyl Groupoid Tristan Bice✩ Institute of Mathematics Czech Academy of Sciences Zitn´a25,ˇ 115 67 Prague, Czech Republic Abstract We unify the Kumjian-Renault Weyl groupoid construction with the Lawson- Lenz version of Exel’s tight groupoid construction. We do this by utilising only a weak algebraic fragment of the C*-algebra structure, namely its *-semigroup reduct. Fundamental properties like local compactness are also shown to remain valid in general classes of *-rings. Keywords: Weyl groupoid, tight groupoid, C*-algebra, inverse semigroup, *-semigroup, *-ring 2010 MSC: 06F05, 20M25, 20M30, 22A22, 46L05, 46L85, 47D03 1. Introduction 1.1. Background Renault’s groundbreaking thesis [Ren80] revealed the striking interplay be- tween ´etale groupoids and the C*-algebras they give rise to. Roughly speaking, the ´etale groupoid provides a more topological picture of the corresponding C*-algebra, with various key properties of the algebra, like nuclearity and sim- plicity (see [ADR00] and [CEP+19]), being determined in a straightforward way from the underlying ´etale groupoid. Naturally, this has led to the quest to find appropriate ´etale groupoid models for various C*-algebras. Two general methods have emerged for finding such models, namely arXiv:1911.08812v3 [math.OA] 20 Sep 2020 1. Exel’s tight groupoid construction from an inverse semigroup, and 2. Kumjian-Renault’s Weyl groupoid construction from a Cartan C*-subalgebra (see [Exe08], [Kum86] and [Ren08]). However, both of these have their limi- tations. For example, tight groupoids are always ample, which means the cor- responding C*-algebras always have lots of projections. On the other hand, the Weyl groupoid is always effective, which discounts many naturally arising groupoids. -
Introduction (Lecture 1)
Introduction (Lecture 1) February 3, 2009 One of the basic problems of manifold topology is to give a classification for manifolds (of some fixed dimension n) up to diffeomorphism. In the best of all possible worlds, a solution to this problem would provide the following: (i) A list of n-manifolds fMαg, containing one representative from each diffeomorphism class. (ii) A procedure which determines, for each n-manifold M, the unique index α such that M ' Mα. In the case n = 2, it is possible to address these problems completely: a connected oriented surface Σ is classified up to homeomorphism by a single integer g, called the genus of Σ. For each g ≥ 0, there is precisely one connected surface Σg of genus g up to diffeomorphism, which provides a solution to (i). Given an arbitrary connected oriented surface Σ, we can determine its genus simply by computing its Euler characteristic χ(Σ), which is given by the formula χ(Σ) = 2 − 2g: this provides the procedure required by (ii). Given a solution to the classification problem satisfying the demands of (i) and (ii), we can extract an algorithm for determining whether two n-manifolds M and N are diffeomorphic. Namely, we apply the procedure (ii) to extract indices α and β such that M ' Mα and N ' Mβ: then M ' N if and only if α = β. For example, suppose that n = 2 and that M and N are connected oriented surfaces with the same Euler characteristic. Then the classification of surfaces tells us that there is a diffeomorphism φ from M to N. -
A Class of Totally Geodesic Foliations of Lie Groups
Proc. Indian Acad. Sci. (Math. Sci.), Vol. 100, No. 1, April 1990, pp. 57-64. ~2 Printed in India. A class of totally geodesic foliations of Lie groups G SANTHANAM School of Mathematics. Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India MS received 4 October 1988; revised 25 May 1989 A~traet. This paper is devoted to classifying the foliations of G with leaves of the form .qKh - t where G is a compact, connected and simply connected L,c group and K is a connected closed subgroup of G such that G/K is a rank-I Riemannian symmetric space. In the case when G/K =S", the homotopy type of space of such foliations is also given. Keywords. Foliations; rank-I Riemannian symmetric space; cutlocus. I. Introduction The study of fibrations of spheres by great spheres is a very interesting problem in geometry and it is very important in the theory of Blaschke manifolds. In [l], Gluck and Warner have studied the great circle fibrations of the three spheres. In that paper they have proved very interesting results. When we look at the problem group theoretically, we see that all the results of [1] go through, for foliations of G with leaves of the form gKh- 1 where G is a compact, connected and simply connected Lie group and K is a connected closed subgroup of G such that G/K is a rank- l Riemannian symmetric space (see [-2]), except perhaps the theorem 3 for the pair (G, K) such that G/K=CP n, HP ~ etc. -
What Does a Lie Algebra Know About a Lie Group?
WHAT DOES A LIE ALGEBRA KNOW ABOUT A LIE GROUP? HOLLY MANDEL Abstract. We define Lie groups and Lie algebras and show how invariant vector fields on a Lie group form a Lie algebra. We prove that this corre- spondence respects natural maps and discuss conditions under which it is a bijection. Finally, we introduce the exponential map and use it to write the Lie group operation as a function on its Lie algebra. Contents 1. Introduction 1 2. Lie Groups and Lie Algebras 2 3. Invariant Vector Fields 3 4. Induced Homomorphisms 5 5. A General Exponential Map 8 6. The Campbell-Baker-Hausdorff Formula 9 Acknowledgments 10 References 10 1. Introduction Lie groups provide a mathematical description of many naturally-occuring sym- metries. Though they take a variety of shapes, Lie groups are closely linked to linear objects called Lie algebras. In fact, there is a direct correspondence between these two concepts: simply-connected Lie groups are isomorphic exactly when their Lie algebras are isomorphic, and every finite-dimensional real or complex Lie algebra occurs as the Lie algebra of a simply-connected Lie group. To put it another way, a simply-connected Lie group is completely characterized by the small collection n2(n−1) of scalars that determine its Lie bracket, no more than 2 numbers for an n-dimensional Lie group. In this paper, we introduce the basic Lie group-Lie algebra correspondence. We first define the concepts of a Lie group and a Lie algebra and demonstrate how a certain set of functions on a Lie group has a natural Lie algebra structure.