Combinatorics And Topology Related To Involutions In Coxeter Groups
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Combinatorics And Topology Related To Involutions In Coxeter Groups
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Author : Mikael Hansson
language : en
Publisher: Linköping University Electronic Press
Release Date : 2018-05-21
Combinatorics And Topology Related To Involutions In Coxeter Groups written by Mikael Hansson and has been published by Linköping University Electronic Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-05-21 with categories.
This dissertation consists of three papers in combinatorial Coxeter group theory. A Coxeter group is a group W generated by a set S, where all relations can be derived from the relations s2 = e for all s ?? S, and (ss?)m(s,s?) = e for some pairs of generators s ? s? in S, where e ?? W is the identity element and m(s, s?) is an integer satisfying that m(s, s?) = m(s?, s) ? 2. Two prominent examples of Coxeter groups are provided by the symmetric group Sn (i.e., the set of permutations of {1, 2, . . . , n}) and finite reflection groups (i.e., finite groups generated by reflections in some real euclidean space). There are also important infinite Coxeter groups, e.g., affine reflection groups. Every Coxeter group can be equipped with various natural partial orders, the most important of which is the Bruhat order. Any subset of a Coxeter group can then be viewed as an induced subposet. In Paper A, we study certain posets of this kind, namely, unions of conjugacy classes of involutions in the symmetric group. We obtain a complete classification of the posets that are pure (i.e., all maximal chains have the same length). In particular, we prove that the set of involutions with exactly one fixed point is pure, which settles a conjecture of Hultman in the affirmative. When the posets are pure, we give their rank functions. We also give a short, new proof of the EL-shellability of the set of fixed-point-free involutions, established by Can, Cherniavsky, and Twelbeck. Paper B also deals with involutions in Coxeter groups. Given an involutive automorphism ? of a Coxeter system (W, S), let ?(?) = {w ?? W | ?(w) = w?1} be the set of twisted involutions. In particular, ?(id) is the set of ordinary involutions in W. It is known that twisted involutions can be represented by words in the alphabet = { | s ?? S}, called -expressions. If ss? has finite order m(s, s?), let a braid move be the replacement of ? ? by ? ? ?, both consisting of m(s, s?) letters. We prove a word property for ?(?), for any Coxeter system (W, S) with any ?. More precisely, we provide a minimal set of moves, easily determined from the Coxeter graph of (W, S), that can be added to the braid moves in order to connect all reduced -expressions for any given w ?? ?(?). This improves upon a result of Hamaker, Marberg, and Pawlowski, and generalises similar statements valid in certain types due to Hu, Zhang, Wu, and Marberg. In Paper C, we investigate the topology of (the order complexes of) certain posets, called pircons. A special partial matching (SPM) on a poset is a matching of the Hasse diagram satisfying certain extra conditions. An SPM without fixed points is precisely a special matching as defined by Brenti. Let a pircon be a poset in which every non-trivial principal order ideal is finite and admits an SPM. Thus pircons generalise Marietti’s zircons. Our main result is that every open interval in a pircon is a PL ball or a PL sphere. An important subset of ?(?) is the set ??(?) = {?(w?1)w | w ?? W} of twisted identities. We prove that if ? does not flip any edges with odd labels in the Coxeter graph, then ??(?), with the order induced by the Bruhat order on W, is a pircon. Hence, its open intervals are PL balls or spheres, which confirms a conjecture of Hultman. It is also demonstrated that Bruhat orders on Rains and Vazirani’s quasiparabolic W-sets (under a boundedness assumption) form pircons. In particular, this applies to all parabolic quotients of Coxeter groups.
Combinatorics Of Coxeter Groups
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Author : Anders Bjorner
language : en
Publisher: Springer Science & Business Media
Release Date : 2006-02-25
Combinatorics Of Coxeter Groups written by Anders Bjorner and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006-02-25 with Mathematics categories.
Includes a rich variety of exercises to accompany the exposition of Coxeter groups Coxeter groups have already been exposited from algebraic and geometric perspectives, but this book will be presenting the combinatorial aspects of Coxeter groups
The Isomorphism Problem In Coxeter Groups
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Author : C. Patrick Bahls
language : en
Publisher: World Scientific
Release Date : 2005
The Isomorphism Problem In Coxeter Groups written by C. Patrick Bahls and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with Mathematics categories.
The book is the first to give a comprehensive overview of the techniques and tools currently being used in the study of combinatorial problems in Coxeter groups. It is self-contained, and accessible even to advanced undergraduate students of mathematics.The primary purpose of the book is to highlight approximations to the difficult isomorphism problem in Coxeter groups. A number of theorems relating to this problem are stated and proven. Most of the results addressed here concern conditions which can be seen as varying degrees of uniqueness of representations of Coxeter groups. Throughout the investigation, the readers are introduced to a large number of tools in the theory of Coxeter groups, drawn from dozens of recent articles by prominent researchers in geometric and combinatorial group theory, among other fields. As the central problem of the book may in fact be solved soon, the book aims to go further, providing the readers with many techniques that can be used to answer more general questions. The readers are challenged to practice those techniques by solving exercises, a list of which concludes each chapter.
Generalized Noncrossing Partitions And Combinatorics Of Coxeter Groups
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Author : Drew Douglas Armstrong
language : en
Publisher: American Mathematical Soc.
Release Date : 2006
Generalized Noncrossing Partitions And Combinatorics Of Coxeter Groups written by Drew Douglas Armstrong and has been published by American Mathematical Soc. this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
Quotients Of Coxeter Complexes And P Partitions
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Author : Victor Reiner
language : en
Publisher: American Mathematical Soc.
Release Date : 1992-01-01
Quotients Of Coxeter Complexes And P Partitions written by Victor Reiner and has been published by American Mathematical Soc. this book supported file pdf, txt, epub, kindle and other format this book has been release on 1992-01-01 with Mathematics categories.
This work deals with Coxeter complexes, a class of highly symmetrical triangulations of spheres and their quotients by symmetry subgroups. For certain subgroups, the author shows how the combinatorial theory of P-partitions may be used to analyse the quotient and how P-partitions and multipartite P-partitions may be extended to deal with more general classes of subgroups. Applications to combinatorics, topology, and invariant theory of finite groups are discussed.
The Geometry And Topology Of Coxeter Groups
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Author : Michael Davis
language : en
Publisher: Princeton University Press
Release Date : 2008
The Geometry And Topology Of Coxeter Groups written by Michael Davis and has been published by Princeton University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with Mathematics categories.
The Geometry and Topology of Coxeter Groups is a comprehensive and authoritative treatment of Coxeter groups from the viewpoint of geometric group theory. Groups generated by reflections are ubiquitous in mathematics, and there are classical examples of reflection groups in spherical, Euclidean, and hyperbolic geometry. Any Coxeter group can be realized as a group generated by reflection on a certain contractible cell complex, and this complex is the principal subject of this book. The book explains a theorem of Moussong that demonstrates that a polyhedral metric on this cell complex is nonpositively curved, meaning that Coxeter groups are "CAT(0) groups." The book describes the reflection group trick, one of the most potent sources of examples of aspherical manifolds. And the book discusses many important topics in geometric group theory and topology, including Hopf's theory of ends; contractible manifolds and homology spheres; the Poincaré Conjecture; and Gromov's theory of CAT(0) spaces and groups. Finally, the book examines connections between Coxeter groups and some of topology's most famous open problems concerning aspherical manifolds, such as the Euler Characteristic Conjecture and the Borel and Singer conjectures.
Applications Of Group Theory To Combinatorics
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Author : Jack Koolen
language : en
Publisher: CRC Press
Release Date : 2008-07-02
Applications Of Group Theory To Combinatorics written by Jack Koolen and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008-07-02 with Mathematics categories.
Applications of Group Theory to Combinatorics contains 11 survey papers from international experts in combinatorics, group theory and combinatorial topology. The contributions cover topics from quite a diverse spectrum, such as design theory, Belyi functions, group theory, transitive graphs, regular maps, and Hurwitz problems, and present the state
Combinatorial Group Theory
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Author : Daniel E. Cohen
language : en
Publisher: Cambridge University Press
Release Date : 1989-08-17
Combinatorial Group Theory written by Daniel E. Cohen and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1989-08-17 with Mathematics categories.
In this book the author aims to show the value of using topological methods in combinatorial group theory.
Combinatorial Group Theory And Topology
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Author : S. M. Gersten
language : en
Publisher: Princeton University Press
Release Date : 1987-05-21
Combinatorial Group Theory And Topology written by S. M. Gersten and has been published by Princeton University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1987-05-21 with Mathematics categories.
Group theory and topology are closely related. The region of their interaction, combining the logical clarity of algebra with the depths of geometric intuition, is the subject of Combinatorial Group Theory and Topology. The work includes papers from a conference held in July 1984 at Alta Lodge, Utah. Contributors to the book include Roger Alperin, Hyman Bass, Max Benson, Joan S. Birman, Andrew J. Casson, Marshall Cohen, Donald J. Collins, Robert Craggs, Michael Dyer, Beno Eckmann, Stephen M. Gersten, Jane Gilman, Robert H. Gilman, Narain D. Gupta, John Hempel, James Howie, Roger Lyndon, Martin Lustig, Lee P. Neuwirth, Andrew J. Nicas, N. Patterson, John G. Ratcliffe, Frank Rimlinger, Caroline Series, John R. Stallings, C. W. Stark, and A. Royce Wolf.
Combinatorial And Geometric Group Theory
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Author : Oleg Bogopolski
language : en
Publisher: Springer Science & Business Media
Release Date : 2011-01-28
Combinatorial And Geometric Group Theory written by Oleg Bogopolski and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-01-28 with Mathematics categories.
This volume assembles several research papers in all areas of geometric and combinatorial group theory originated in the recent conferences in Dortmund and Ottawa in 2007. It contains high quality refereed articles developing new aspects of these modern and active fields in mathematics. It is also appropriate to advanced students interested in recent results at a research level.