In mathematics, specifically in group theory, two groups are commensurable if they differ only by a finite amount, in a precise sense. The commensurator of a subgroup is another subgroup, related to the normalizer. (Wikipedia).
You might find that for certain groups, the commutative property hold. In this video we will assume the existence of such a group and prove a few properties that it may have, by way of some example problems.
From playlist Abstract algebra
AlgTopReview4: Free abelian groups and non-commutative groups
Free abelian groups play an important role in algebraic topology. These are groups modelled on the additive group of integers Z, and their theory is analogous to the theory of vector spaces. We state the Fundamental Theorem of Finitely Generated Commutative Groups, which says that any such
From playlist Algebraic Topology
Group theory 2: Cayley's theorem
This is lecture 2 of an online mathematics course on group theory. It describes Cayley's theorem that every abstract group is the group of symmetries of something, and as examples shows the Cayley graphs of the Klein 4-group and the symmetric group on 3 points.
From playlist Group theory
This is lecture 1 of an online mathematics course on group theory. This lecture defines groups and gives a few examples of them.
From playlist Group theory
Chapter 5: Quotient groups | Essence of Group Theory
Quotient groups is a very important concept in group theory, because it has paramount importance in group homomorphisms (connection with the isomorphism theorem(s)). With this video series, abstract algebra needs not be abstract - one can easily develop intuitions for group theory! In fac
From playlist Essence of Group Theory
Commutative algebra 53: Dimension Introductory survey
This lecture is part of an online course on commutative algebra, following the book "Commutative algebra with a view toward algebraic geometry" by David Eisenbud. We give an introductory survey of many different ways of defining dimension. Reading: Section Exercises:
From playlist Commutative algebra
Spectra in locally symmetric spaces by Alan Reid
PROGRAM ZARISKI-DENSE SUBGROUPS AND NUMBER-THEORETIC TECHNIQUES IN LIE GROUPS AND GEOMETRY (ONLINE) ORGANIZERS: Gopal Prasad, Andrei Rapinchuk, B. Sury and Aleksy Tralle DATE: 30 July 2020 VENUE: Online Unfortunately, the program was cancelled due to the COVID-19 situation but it will
From playlist Zariski-dense Subgroups and Number-theoretic Techniques in Lie Groups and Geometry (Online)
Commensurators of thin Subgroups by Mahan M. J.
PROGRAM SMOOTH AND HOMOGENEOUS DYNAMICS ORGANIZERS: Anish Ghosh, Stefano Luzzatto and Marcelo Viana DATE: 23 September 2019 to 04 October 2019 VENUE: Ramanujan Lecture Hall, ICTS Bangalore Ergodic theory has its origins in the the work of L. Boltzmann on the kinetic theory of gases.
From playlist Smooth And Homogeneous Dynamics
AlgTopReview2: Introduction to group theory
This lecture gives a brief overview or introduction to group theory, concentrating on commutative groups (future lectures will talk about the non-commutative case). We generally use additive notation + for the operation in a commutative group, and 0 for the (additive) inverse. The main sta
From playlist Algebraic Topology
2020 Theory Winter School: Oskar Vafek
Topic: Topology and interactions in twisted bilayer graphene narrow bands For more information on the 2020 Theory Winter School: https://nationalmaglab.org/news-events/events/for-scientists/winter-theory-school
From playlist 2020 Theory Winter School
Ax-Lindemann-Weierstrass Theorem (ALW) for Fuchsian automorphic functions - Joel Nagloo
Joint IAS/Princeton University Number Theory Seminar Topic: Ax-Lindemann-Weierstrass Theorem (ALW) for Fuchsian automorphic functions Speaker: Joel Nagloo Affiliation: City University of New York Date: January 21, 2021 For more video please visit http://video.ias.edu
From playlist Mathematics
Camille Horbez: Measure equivalence and right-angled Artin groups
Given a finite simple graph X, the right-angled Artin group associated to X is defined by the following very simple presentation: it has one generator per vertex of X, and the only relations consist in imposing that two generators corresponding to adjacent vertices commute. We investigate
From playlist Geometry
Emergent geometric frustration and flat bands in twisted bilayer graphene by Hridis Kumar Pal
DISCUSSION MEETING NOVEL PHASES OF QUANTUM MATTER ORGANIZERS: Adhip Agarwala, Sumilan Banerjee, Subhro Bhattacharjee, Abhishodh Prakash and Smitha Vishveshwara DATE: 23 December 2019 to 02 January 2020 VENUE: Ramanujan Lecture Hall, ICTS Bangalore Recent theoretical and experimental
From playlist Novel Phases of Quantum Matter 2019
Geometric structures and thin groups II - Darren Long
Speaker: Darren Long (UCSB) Title: Geometric structures and thin groups II Abstract: In these two talks we will discuss situations in which geometric input can be used as a method to certify that a group is thin. This involves a mix of theory and computation.
From playlist Mathematics
Uri Bader - 3/4 Algebraic Representations of Ergodic Actions
Ergodic Theory is a powerful tool in the study of linear groups. When trying to crystallize its role, emerges the theory of AREAs, that is Algebraic Representations of Ergodic Actions, which provides a categorical framework for various previously studied concepts and methods. Roughly, this
From playlist Uri Bader - Algebraic Representations of Ergodic Actions
Piotr Przytycki: Torsion groups do not act on 2-dimensional CAT(0) complexes
We show, under mild hypotheses, that if each element of a finitely generated group acting on a 2-dimensional CAT(0) complex has a fixed point, then the action is trivial. In particular, all actions of finitely generated torsion groups on such complexes are trivial. As an ingredient, we pro
From playlist Geometry
Visual Group Theory, Lecture 3.5: Quotient groups
Visual Group Theory, Lecture 3.5: Quotient groups Like how a direct product can be thought of as a way to "multiply" two groups, a quotient is a way to "divide" a group by one of its subgroups. We start by defining this in terms of collapsing Cayley diagrams, until we get a conjecture abo
From playlist Visual Group Theory
What is a Group? | Abstract Algebra
Welcome to group theory! In today's lesson we'll be going over the definition of a group. We'll see the four group axioms in action with some examples, and some non-examples as well which violate the axioms and are thus not groups. In a fundamental way, groups are structures built from s
From playlist Abstract Algebra
Commensurability between right-angled Coxeter & Artin groups-Prof. Pallavi Dani (Louisiana State U.)
A common theme in geometric group theory is to try to understand when two groups are quasi-isometric (or "geometrically close") and when they are commensurable (or "algebraically close"), and when these two notions coincide. Davis-Januszkiewicz showed that every right-angled Artin group (R
Definition of a group Lesson 24
In this video we take our first look at the definition of a group. It is basically a set of elements and the operation defined on them. If this set of elements and the operation defined on them obey the properties of closure and associativity, and if one of the elements is the identity el
From playlist Abstract algebra