Group with operators
From Wikipedia, the free encyclopedia
In abstract algebra, a branch of pure mathematics, the algebraic structure group with operators or Ω-group is a group with a set of group endomorphisms.
Groups with operators were extensively studied by Emmy Noether and her school in the 1920s. She employed the concept in her original formulation of the three Noether isomorphism theorems.
Contents |
[edit] Definition
A group with operators (G, Ω) is a group G together with a family of functions Ω:
which are distributive with respect to the group operation. Ω is called the operator domain, and its elements are called the homotheties of G.
We denote the image of a group element g under a function ω with gω. The distributivity can then be expressed as
A subgroup S of G is called a stable subgroup, ω-subgroup or Ω-invariant subgroup if it respects the hometheties, that is
[edit] Category theoretic remarks
In category theory, a group with operators can be defined as an object of a functor category GrpM where M is a monoid (i.e., a category with one object) and Grp denotes the category of groups. This definition is equivalent to the previous one.
A group with operators is also a mapping
where 
is the set of group endomorphisms of G.
[edit] Examples
- Given any group G, (G, ∅) is trivially a group with operators
- Given an R-module M, the group R operates on the operator domain M by scalar multiplication. More concretely, every vector space is a group with operators.
[edit] See also
[edit] References
- Bourbaki, Nicolas (1998). Elements of Mathematics : Algebra I Chapters 1-3. Springer-Verlag. ISBN 3-540-64243-9.
