Coding With Fun
Home Docker Django Node.js Articles Python pip guide FAQ Policy

Is the dihedral group a rotation group or a symmetry group?


Asked by Hadleigh Cole on Dec 04, 2021 FAQ



The dihedral group as symmetry group in 2D and rotation group in 3D. This is the symmetry group of a regular polygon with n sides (for n ≥ 3; this extends to the cases n = 1 and n = 2 where we have a plane with respectively a point offset from the "center" of the "1-gon" and a "2-gon" or line segment).
In this manner,
The symmetries of this pentagon are linear transformations of the plane as a vector space. If we center the regular polygon at the origin, then elements of the dihedral group act as linear transformations of the plane. This lets us represent elements of D n as matrices, with composition being matrix multiplication.
Moreover, D 2, which is isomorphic to the Klein four-group, is the symmetry group of a non-equilateral rectangle. This figure has four symmetry operations: the identity operation, one twofold axis of rotation, and two nonequivalent mirror planes. D 3, D 4 etc. are the symmetry groups of the regular polygons.
In addition,
The notation for the dihedral group differs in geometry and abstract algebra. In geometry, Dn or Dihn refers to the symmetries of the n -gon, a group of order 2n. In abstract algebra, D2n refers to this same dihedral group. The geometric convention is used in this article.
Thereof,
The generalized dihedral group corresponding to the cyclic group of order four. The holomorph of the cyclic group of order four. The external wreath product of the cyclic group of order two with the cyclic group of order two, acting via the regular action.