Vierergruppe: Difference between revisions
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In [[group theory]], a branch of [[mathematics]], the '''Vierergruppe''' (German, meaning group of four) is the smallest [[cyclic group|non-cyclic group]]. It is an [[Abelian group| Abelian (commutative) group]] of order 4. | In [[group theory]], a branch of [[mathematics]], the '''Vierergruppe''' (German, meaning group of four) is the smallest [[cyclic group|non-cyclic group]]. It is an [[Abelian group| Abelian (commutative) group]] of order 4. | ||
The group was given his name by [[Felix Klein]] in his 1884 lectures "''Vorlesungen über das Ikosaeder und die Auflösung der Gleichungen vom fünften Grade''" (lectures on the Icosahedron and the solution of equations of the fifth degree). Since in German the cardinal "four" starts with the letter V (vier) Klein introduced the symbol ''V''. | The group was given his name by [[Felix Klein]] in his 1884 lectures "''Vorlesungen über das Ikosaeder und die Auflösung der Gleichungen vom fünften Grade''" (lectures on the Icosahedron and the solution of equations of the fifth degree).<ref>[http://www.archive.org/stream/vorlesungenber00kleiuoft#page/n5/mode/2up Klein's lectures online]</ref> Since in German the cardinal "four" starts with the letter V (vier) Klein introduced the symbol ''V''. | ||
== Multiplication table == | == Multiplication table == | ||
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This table is symmetric, meaning that the elements commute: ''ab'' = ''ba'', etc. The elements not equal to the identity ''e'' have the property ''g''<sup>2</sup> = ''e'' (these elements are of order 2). | This table is symmetric, meaning that the elements commute: ''ab'' = ''ba'', etc. The elements not equal to the identity ''e'' have the property ''g''<sup>2</sup> = ''e'' (these elements are of order 2). | ||
==Example== | |||
The classic example of a Vierergruppe, first given by Klein, is the set of rotations over 180° around three orthogonal axes, for instance [[Cartesian coordinates|Cartesian axes]], mapping (''x'', ''y'', ''z'') to | |||
::''e:'' (''x'', ''y'', ''z''), | |||
::''a:'' (''x'', ''−y'', ''−z'') | |||
::''b:'' (''−x'', ''y'', ''−z'') | |||
::''c:'' (''−x'', ''−y'', ''z'') | |||
==Reference== | |||
<references /> | |||
Revision as of 10:25, 30 July 2009
In group theory, a branch of mathematics, the Vierergruppe (German, meaning group of four) is the smallest non-cyclic group. It is an Abelian (commutative) group of order 4.
The group was given his name by Felix Klein in his 1884 lectures "Vorlesungen über das Ikosaeder und die Auflösung der Gleichungen vom fünften Grade" (lectures on the Icosahedron and the solution of equations of the fifth degree).[1] Since in German the cardinal "four" starts with the letter V (vier) Klein introduced the symbol V.
Multiplication table
The multiplication table of the group is
V e a b c e e a b c a a e c b b b c e a c c b a e
This table is symmetric, meaning that the elements commute: ab = ba, etc. The elements not equal to the identity e have the property g2 = e (these elements are of order 2).
Example
The classic example of a Vierergruppe, first given by Klein, is the set of rotations over 180° around three orthogonal axes, for instance Cartesian axes, mapping (x, y, z) to
- e: (x, y, z),
- a: (x, −y, −z)
- b: (−x, y, −z)
- c: (−x, −y, z)