Êtes-vous un étudiant de l'EPFL à la recherche d'un projet de semestre?
Travaillez avec nous sur des projets en science des données et en visualisation, et déployez votre projet sous forme d'application sur GraphSearch.
Concept
Torsion (algèbre)
Résumé
In mathematics, specifically in ring theory, a torsion element is an element of a module that yields zero when multiplied by some non-zero-divisor of the ring. The torsion submodule of a module is the submodule formed by the torsion elements. A torsion module is a module that equals its torsion submodule. A module is torsion-free if its torsion submodule comprises only the zero element.
This terminology is more commonly used for modules over a domain, that is, when the regular elements of the ring are all its nonzero elements.
This terminology applies to abelian groups (with "module" and "submodule" replaced by "group" and "subgroup"). This is allowed by the fact that the abelian groups are the modules over the ring of integers (in fact, this is the origin of the terminology, that has been introduced for abelian groups before being generalized to modules).
In the case of groups that are noncommutative, a torsion element is an element of finite order. Contrary to the commutative case, the torsion elements do not form a subgroup, in general.
An element m of a module M over a ring R is called a torsion element of the module if there exists a regular element r of the ring (an element that is neither a left nor a right zero divisor) that annihilates m, i.e., r m = 0.
In an integral domain (a commutative ring without zero divisors), every non-zero element is regular, so a torsion element of a module over an integral domain is one annihilated by a non-zero element of the integral domain. Some authors use this as the definition of a torsion element, but this definition does not work well over more general rings.
A module M over a ring R is called a torsion module if all its elements are torsion elements, and torsion-free if zero is the only torsion element. If the ring R is an integral domain then the set of all torsion elements forms a submodule of M, called the torsion submodule of M, sometimes denoted T(M). If R is not commutative, T(M) may or may not be a submodule.
Source officielle
À propos de ce résultat
Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.
Publications associées (2)
Personnes associées (1)
Concepts associés (47)
Torsion subgroup
In the theory of abelian groups, the torsion subgroup AT of an abelian group A is the subgroup of A consisting of all elements that have finite order (the torsion elements of A). An abelian group A is called a torsion group (or periodic group) if every element of A has finite order and is called torsion-free if every element of A except the identity is of infinite order. The proof that AT is closed under the group operation relies on the commutativity of the operation (see examples section).
Finitely generated group
In algebra, a finitely generated group is a group G that has some finite generating set S so that every element of G can be written as the combination (under the group operation) of finitely many elements of S and of inverses of such elements. By definition, every finite group is finitely generated, since S can be taken to be G itself. Every infinite finitely generated group must be countable but countable groups need not be finitely generated. The additive group of rational numbers Q is an example of a countable group that is not finitely generated.
Torsion (algèbre)
En algèbre, dans un groupe, un élément est dit de torsion s'il est d'ordre fini, c'est-à-dire si l'une de ses puissances non nulle est l'élément neutre. La torsion d'un groupe est l'ensemble de ses éléments de torsion. Un groupe est dit sans torsion si sa torsion ne contient que le neutre, c'est-à-dire si tout élément différent du neutre est d'ordre infini. Si le groupe est abélien, sa torsion est un sous-groupe. Par exemple, le sous-groupe de torsion du groupe abélien est .
Cours associés (10)
MATH-311: Rings and modules
The students are going to solidify their knowledge of ring and module theory with a major emphasis on commutative algebra and a minor emphasis on homological algebra.
MATH-506: Topology IV.b - cohomology rings
Singular cohomology is defined by dualizing the singular chain complex for spaces. We will study its basic properties, see how it acquires a multiplicative structure and becomes a graded commutative a
MATH-510: Modern algebraic geometry
The aim of this course is to learn the basics of the modern scheme theoretic language of algebraic geometry.
Séances de cours associées (89)
Cohomologie de groupe
Couvre le concept de cohomologie de groupe, se concentrant sur les complexes de chaîne, les complexes de cochain, les produits de tasse et les anneaux de groupe.
Théorème algébrique de la Kunneth
Couvre le théorème algébrique de la Kunneth, expliquant les complexes de chaîne et les calculs de cohomologie.
Séquences exactes: Remarques de fractionnement
Explore les séquences exactes divisées en théorie de groupe en mettant l'accent sur la caractérisation et les isomorphismes.