In mathematics, the outer automorphism group of a group, G, is the quotient, Aut(G) / Inn(G), where Aut(G) is the automorphism group of G and Inn(G) is the subgroup consisting of inner automorphisms. The outer automorphism group is usually denoted Out(G). If Out(G) is trivial and G has a trivial center, then G is said to be complete.
An automorphism of a group that is not inner is called an outer automorphism. The cosets of Inn(G) with respect to outer automorphisms are then the elements of Out(G); this is an instance of the fact that quotients of groups are not, in general, (isomorphic to) subgroups. If the inner automorphism group is trivial (when a group is abelian), the automorphism group and outer automorphism group are naturally identified; that is, the outer automorphism group does act on the group.
For example, for the alternating group, A_n, the outer automorphism group is usually the group of order 2, with exceptions noted below. Considering A_n as a subgroup of the symmetric group, S_n, conjugation by any odd permutation is an outer automorphism of A_n or more precisely "represents the class of the (non-trivial) outer automorphism of A_n", but the outer automorphism does not correspond to conjugation by any particular odd element, and all conjugations by odd elements are equivalent up to conjugation by an even element.
The Schreier conjecture asserts that Out(G) is always a solvable group when G is a finite simple group. This result is now known to be true as a corollary of the classification of finite simple groups, although no simpler proof is known.
The outer automorphism group is dual to the center in the following sense: conjugation by an element of G is an automorphism, yielding a map σ : G → Aut(G). The kernel of the conjugation map is the center, while the cokernel is the outer automorphism group (and the image is the inner automorphism group). This can be summarized by the exact sequence:
Z(G) ↪ G Aut(G) ↠ Out(G).
The outer automorphism group of a group acts on conjugacy classes, and accordingly on the character table.
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.
Quantum computing has received wide-spread attention lately due the possibility of a near-term breakthrough of quantum supremacy. This course acts as an introduction to the area of quantum computing.
Après une introduction à la théorie des catégories, nous appliquerons la théorie générale au cas particulier des groupes, ce qui nous permettra de bien mettre en perspective des notions telles que quo
In mathematics, D3 (sometimes alternatively denoted by D6) is the dihedral group of degree 3 and order 6. It equals the symmetric group S3. It is also the smallest non-abelian group. This page illustrates many group concepts using this group as example. The dihedral group D3 is the symmetry group of an equilateral triangle, that is, it is the set of all transformations such as reflection, rotation, and combinations of these, that leave the shape and position of this triangle fixed.
En mathématiques et plus précisément en théorie des groupes, le groupe des quaternions est l'un des deux groupes non abéliens d'ordre 8. Il admet une représentation réelle irréductible de degré 4, et la sous-algèbre des matrices 4×4 engendrée par son image est un corps gauche qui s'identifie au corps des quaternions de Hamilton. Le groupe des quaternions est souvent désigné par le symbole Q ou Q8 et est écrit sous forme multiplicative, avec les 8 éléments suivants : Ici, 1 est l'élément neutre, et pour tout a dans Q.
En mathématiques, un groupe de type de Lie G(k) est un groupe (non nécessairement fini) de points rationnels d'un groupe algébrique linéaire réductif G à valeur dans le corps commutatif k. La classification des groupes simples finis montre que les groupes de types de Lie finis forment l'essentiel des groupes finis simples. Des cas particuliers incluent les groupes classiques, les groupes de Chevalley, les groupes de Steinberg et les groupes de Suzuki-Ree.
We discuss anomalies associated with outer automorphisms in gauge theories based on classical groups, namely charge conjugations for SU(N) and parities for SO(2r). We emphasize the inequivalence (yet related by a flavor transformation) between two versions ...
The beginning of 21st century provided us with many answers about how to reach the channel capacity. Polarization and spatial coupling are two techniques for achieving the capacity of binary memoryless symmetric channels under low-complexity decoding algor ...
EPFL2022
,
The recently introduced polar codes constitute a breakthrough in coding theory due to their capacity-achieving property. This goes hand in hand with a quasilinear construction, encoding, and successive cancellation list decoding procedures based on the Plo ...