请输入您要查询的字词:

 

单词 Hypergroup
释义

hypergroup


Hypergroups are generalizationsPlanetmathPlanetmath of groups. Recall that a group is set with a binary operationMathworldPlanetmath on it satisfying a number of conditions. If this binary operation is taken to be multivalued, then we arrive at a hypergroup. In order to make this precise, we need some preliminary concepts:

Definition. A hypergroupoid, or multigroupoid, is a non-empty set G, together with a multivalued function :G×GG called the multiplication on G.

We write ab, or simply ab, instead of (a,b). Furthermore, if ab={c}, then we use the abbreviation ab=c.

A hypergroupoid is said to be commutativePlanetmathPlanetmathPlanetmath if ab=ba for all a,bG. Defining associativity of on G, however, is trickier:

Given a hypergroupoid G, the multiplication induces a binary operation (also written ) on P(G), the powerset of P, given by

AB:={abaA and bB}.

As a result, we have an induced groupoidPlanetmathPlanetmathPlanetmathPlanetmath P(G). Instead of writing {a}B, A{b}, and {a}{b}, we write aB,Ab, and ab instead. From now on, when we write (ab)c, we mean“first, take the productMathworldPlanetmath of a and b via the multivalued binary operation on G, then take the product of the set ab with the element c, under the induced binary operation on P(G)”. Given a hypergroupoid G, there are two types of associativity we may define:

Type 1.

(ab)ca(bc), and

Type 2.

a(bc)(ab)c.

G is said to be associative if it satisfies both types of associativity laws. An associative hypergroupoid is called a hypersemigroup. We are now ready to formally define a hypergroup.

Definition. A hypergroup is a hypersemigroup G such that aG=Ga=G for all aG.

For example, let G be a group and H a subgroupMathworldPlanetmathPlanetmath of G. Let M be the collectionMathworldPlanetmath of all left cosetsMathworldPlanetmath of H in G. For aH,bHM, set

aHbH:={cHc=ahbhH}.

Then M is a hypergroup with multiplication .

If the multiplication in a hypergroup G is single-valued, then G is a 2-group (http://planetmath.org/PolyadicSemigroup), and therefore a group (see proof here (http://planetmath.org/PolyadicSemigroup)).

Remark. A hypergroup is also known as a multigroup, although some call a multigroup as a hypergroup with a designated identity elementMathworldPlanetmath e, as well as a designated inverseMathworldPlanetmathPlanetmathPlanetmathPlanetmath for every element with respect e. Actually identities and inverses may be defined more generally for hypergroupoids:

Let G be a hypergroupoid. Identity elements are defined via the following three sets:

  1. 1.

    (set of left identities): IL(G):={eGaea for all aG},

  2. 2.

    (set of right identities): IR(G):={eGaae for all aG}, and

  3. 3.

    (set of identities): I(G)=IL(G)IR(G).

eL(G) is called an absolute identity if ea=ae=a for all aG. If e,fG are both absolute identities, then e=ef=f, so G can have at most one absolute identity.

Suppose eIL(G)IR(G) and aG. An element bG is said to be a left inverse of a with respect to e if eba. Right inverses of a are defined similarly. If b is both a left and a right inverse of a with respect to e, then b is called an inverse of a with respect to e.

Thus, one may say that a multigroup is a hypergroup G with an identity eG, and a function :-1GG such that a-1:=-1(a) is an inverse of a with respect to e.

In the example above, M is a multigroup in the sense given in the remark above. The designated identity is H (in fact, this is the only identity in M), and for every aHM, its designated inverse is provided by a-1H (of course, this may not be its only inverse, as any bH such that ahb=e for some hH will do).

References

  • 1 R. H. Bruck, A Survey on Binary Systems, Springer-Verlag, New York, 1966.
  • 2 M. Dresher, O. Ore, Theory of Multigroups, Amer. J. Math. vol. 60, pp. 705-733, 1938.
  • 3 J.E. Eaton, O. Ore, Remarks on Multigroups, Amer. J. Math. vol. 62, pp. 67-71, 1940.
  • 4 L. W. Griffiths, On Hypergroups, Multigroups, and Product Systems, Amer. J. Math. vol. 60, pp. 345-354, 1938.
  • 5 A. P. Dičman, On Multigroups whose Elements are Subsets of a Group, Moskov. Gos. Ped. Inst. Uč. Zap. vol. 71, pp. 71-79, 1953

随便看

 

数学辞典收录了18232条数学词条,基本涵盖了常用数学知识及数学英语单词词组的翻译及用法,是数学学习的有利工具。

 

Copyright © 2000-2023 Newdu.com.com All Rights Reserved
更新时间:2025/5/4 11:44:27