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"The theory of buildings lies at the interplay between geometry and group theory, and is one of the main tools for studying the structure of many groups. Actually, buildings were introduced by Jacques Tits in the 1950s to better understand and study a semi-simple algebraic group over a field. For a general field, its associated building is a spherical building, called its Tits building. It is a simplicial complex and, in this book, one considers a geometric realization called vectorial building. When the field is real valued, François Bruhat and Jacques Tits constructed another building taking into account the topology of the field. This Bruhat-Tits building is a polysimplicial complex and its usual geometric realization is an affine building. These vectorial or affine buildings are the main examples of Euclidean buildings. The present book develops the general abstract theory of these Euclidean buildings (the buildings with Euclidean affine spaces as apartments). It is largely self-contained and emphasizes the metric aspects of these objects, as CAT(0) spaces very similar to Riemannian symmetric spaces of non-compact type. The book studies their compactifications, their links with groups, many classical examples, and some applications (for example, to Hecke algebras)."--Provided by publisher.

Buildings (Group theory). --- Geometric group theory. --- Immeubles (Théorie des groupes). --- Théorie géométrique des groupes.

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In this master's thesis, we explore the notion of growth of groups. For any finitely generated group, one can define a growth function associated to a fixed finite set of generators. It is the mapping of any positive integer n to the number of elements of a group that can be written in n generators. This allows for a classification of groups according to their growth, examples of such classes are groups of polynomial growth and groups of exponential growth. In the thesis, we define this concept with the necessary rigor. We then proceed to prove that groups of polynomial growth and virtually nilpotent groups are the same (Gromov's theorem). We also provide an example of a group, the Grigorchuk group, that has neither polynomial nor exponential growth. Dans ce mémoire, on développe la notion de croissance des groupes. Pour tout groupe finiment engendré, on définit la fonction de croissance associée à un système de générateurs finis fixé. C'est la fonction qui à un naturel n associe le nombre d'éléments du groupe qui peuvent être écrits en n générateurs. Une classification des groupes selon leur croissance est possible. On définit par exemple les groupes à croissance polynomiale ou à croissance exponentielle. Dans le mémoire, on définit ce concept avec la rigueur nécessaire. Ensuite, on prouve que les groupes virtuellement nilpotents sont à croissance polynomiale et réciproquement (théorème de Gromov). On donnera également de groupe, le groupe de Grigorchuk, qui n'est ni à croissance polynomiale ni à croissance exponentielle.

Théorie des groupes --- Théorie géométrique des groupes --- Théorème de Gromov --- Croissance des groupes --- Groupe de Grigorchuk --- Groupes nilpotents --- Graphes de Cayley --- Quasi-isométries --- Quasi-isometries --- Group theory --- Geometric group theory --- Gromov's theorem --- Growth of groups --- Grigorchuk group --- Nilpotent groups --- Cayley graphs --- Physique, chimie, mathématiques & sciences de la terre > Mathématiques