Frieze group

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Examples of frieze group patterns

A frieze group is a mathematical concept used to classify designs on two-dimensional surfaces that are repetitive in one direction, according to the symmetries of the pattern. Such patterns occur frequently in architecture and decorative art. The mathematical study of such patterns reveals that exactly seven types of symmetry can occur.

Frieze groups are two-dimensional line groups, having repetition in only one direction. They are related to the more complex wallpaper groups, which classify patterns that are repetitive in two directions, and crystallographic groups, which classify patterns that are repetitive in three directions.

General[edit]

The seven frieze groups
  1. p1: T (translation only, in the horizontal direction)
  2. p1m1: TV (translation and vertical line reflection)
  3. p11m: THG (translation, horizontal line reflection, and glide reflection)
  4. p11g: TG (translation and glide reflection)
  5. p2: TR (translation and 180° rotation)
  6. p2mg: TRVG (translation, 180° rotation, vertical line reflection, and glide reflection)
  7. p2mm: TRHVG (translation, 180° rotation, horizontal line reflection, vertical line reflection, and glide reflection)

Formally, a frieze group is a class of infinite discrete symmetry groups of patterns on a strip (infinitely wide rectangle), hence a class of groups of isometries of the plane, or of a strip. A symmetry group of a frieze group necessarily contains translations and may contain glide reflections, reflections along the long axis of the strip, reflections along the narrow axis of the strip, and 180° rotations. There are seven frieze groups, listed in the summary table. Many authors present the frieze groups in a different order.[1][2]

The actual symmetry groups within a frieze group are characterized by the smallest translation distance, and, for the frieze groups with vertical line reflection or 180° rotation (groups 2, 5, 6, and 7), by a shift parameter locating the reflection axis or point of rotation. In the case of symmetry groups in the plane, additional parameters are the direction of the translation vector, and, for the frieze groups with horizontal line reflection, glide reflection, or 180° rotation (groups 3–7), the position of the reflection axis or rotation point in the direction perpendicular to the translation vector. Thus there are two degrees of freedom for group 1, three for groups 2, 3, and 4, and four for groups 5, 6, and 7.

For two of the seven frieze groups (groups 1 and 4) the symmetry groups are singly generated, for four (groups 2, 3, 5, and 6) they have a pair of generators, and for group 7 the symmetry groups require three generators. A symmetry group in frieze group 1, 2, 3, or 5 is a subgroup of a symmetry group in the last frieze group with the same translational distance. A symmetry group in frieze group 4 or 6 is a subgroup of a symmetry group in the last frieze group with half the translational distance. This last frieze group contains the symmetry groups of the simplest periodic patterns in the strip (or the plane), a row of dots. Any transformation of the plane leaving this pattern invariant can be decomposed into a translation, (x,y) → (n+x,y), optionally followed by a reflection in either the horizontal axis, (x,y) → (x,−y), or the vertical axis, (x,y) → (−x,y), provided that this axis is chosen through or midway between two dots, or a rotation by 180°, (x,y) → (−x,−y) (ditto). Therefore, in a way, this frieze group contains the "largest" symmetry groups, which consist of all such transformations.

The inclusion of the discrete condition is to exclude the group containing all translations, and groups containing arbitrarily small translations (e.g. the group of horizontal translations by rational distances). Even apart from scaling and shifting, there are infinitely many cases, e.g. by considering rational numbers of which the denominators are powers of a given prime number.

The inclusion of the infinite condition is to exclude groups that have no translations:

  • the group with the identity only (isomorphic to C1, the trivial group of order 1).
  • the group consisting of the identity and reflection in the horizontal axis (isomorphic to C2, the cyclic group of order 2).
  • the groups each consisting of the identity and reflection in a vertical axis (ditto)
  • the groups each consisting of the identity and 180° rotation about a point on the horizontal axis (ditto)
  • the groups each consisting of the identity, reflection in a vertical axis, reflection in the horizontal axis, and 180° rotation about the point of intersection (isomorphic to the Klein four-group)

Descriptions of the seven frieze groups[edit]

There are seven distinct subgroups (up to scaling and shifting of patterns) in the discrete frieze group generated by a translation, reflection (along the same axis) and a 180° rotation. Each of these subgroups is the symmetry group of a frieze pattern, and sample patterns are shown in Fig. 1. The seven different groups correspond to the 7 infinite series of axial point groups in three dimensions, with n = ∞.[3]

They are identified using Hermann–Mauguin notation or IUC notation,[4] orbifold notation, Coxeter notation, and Schönflies notation:

Frieze groups
IUC Cox Schön*
Struct.
Diagram§
Orbifold
Examples
nickname
Description
p1 [∞]+
CDel node h2.pngCDel infin.pngCDel node h2.png
C
Z
Frieze group 11.png
∞∞
Frieze example p1.png
Frieze hop.png
hop
(T) Translations only:
This group is singly generated, by a translation by the smallest distance over which the pattern is periodic.
p11g [∞+,2+]
CDel node h2.pngCDel infin.pngCDel node h4.pngCDel 2x.pngCDel node h2.png
S
Z
Frieze group 1g.png
∞×
Frieze example p11g.png
Frieze step.png
step
(TG) Glide-reflections and Translations:
This group is singly generated, by a glide reflection, with translations being obtained by combining two glide reflections.
p1m1 [∞]
CDel node.pngCDel infin.pngCDel node.png
C∞v
Dih
Frieze group m1.png
*∞∞
Frieze example p1m1.png
Frieze sidle.png
sidle
(TV) Vertical reflection lines and Translations:
The group is the same as the non-trivial group in the one-dimensional case; it is generated by a translation and a reflection in the vertical axis.
p2 [∞,2]+
CDel node h2.pngCDel infin.pngCDel node h2.pngCDel 2x.pngCDel node h2.png
D
Dih
Frieze group 12.png
22∞
Frieze example p2.png
Frieze spinning hop.png
spinning hop
(TR) Translations and 180° Rotations:
The group is generated by a translation and a 180° rotation.
p2mg [∞,2+]
CDel node.pngCDel infin.pngCDel node h2.pngCDel 2x.pngCDel node h2.png
D∞d
Dih
Frieze group mg.png
2*∞
Frieze example p2mg.png
Frieze spinning sidle.png
spinning sidle
(TRVG) Vertical reflection lines, Glide reflections, Translations and 180° Rotations:
The translations here arise from the glide reflections, so this group is generated by a glide reflection and either a rotation or a vertical reflection.
p11m [∞+,2]
CDel node h2.pngCDel infin.pngCDel node h2.pngCDel 2.pngCDel node.png
C∞h
Z×Dih1
Frieze group 1m.png
∞*
Frieze example p11m.png
Frieze jump.png
jump
(THG) Translations, Horizontal reflections, Glide reflections:
This group is generated by a translation and the reflection in the horizontal axis. The glide reflection here arises as the composition of translation and horizontal reflection
p2mm [∞,2]
CDel node.pngCDel infin.pngCDel node.pngCDel 2.pngCDel node.png
D∞h
Dih×Dih1
Frieze group mm.png
*22∞
Frieze example p2mm.png
Frieze spinning jump.png
spinning jump
(TRHVG) Horizontal and Vertical reflection lines, Translations and 180° Rotations:
This group requires three generators, with one generating set consisting of a translation, the reflection in the horizontal axis and a reflection across a vertical axis.
*Schönflies's point group notation is extended here as infinite cases of the equivalent dihedral points symmetries
§The diagram shows one fundamental domain in yellow, with reflection lines in blue, glide reflection lines in dashed green, translation normals in red, and 2-fold gyration points as small green squares.

As we have seen, up to isomorphism, there are four groups, two abelian, and two non-abelian.

Lattice types: Oblique and rectangular[edit]

The groups can be classified by their type of two-dimensional grid or lattice.[5] The lattice being oblique means that the second direction need not be orthogonal to the direction of repeat.

Lattice type Groups
Oblique p1, p2
Rectangular p1m1, p11m, p11g, p2mm, p2mg

See also[edit]

Web demo and software[edit]

There exist software graphic tools that create 2D patterns using frieze groups. Usually, the entire pattern is updated automatically in response to edits of the original strip.

  • Kali, a free and open source software application for wallpaper, frieze and other patterns.
  • Kali, free downloadable Kali for Windows and Mac Classic.
  • Tess, a nagware tessellation program for multiple platforms, supports all wallpaper, frieze, and rosette groups, as well as Heesch tilings.
  • FriezingWorkz, a freeware Hypercard stack for the Classic Mac platform that supports all frieze groups.

References[edit]

  1. ^ Coxeter, H. S. M. (1969). Introduction to Geometry. New York: John Wiley & Sons. pp. 47–49. ISBN 0-471-50458-0. 
  2. ^ Cederberg, Judith N. (2001). A Course in Modern Geometries, 2nd ed. New York: Springer-Verlag. pp. 117–118, 165–171. ISBN 0-387-98972-2. 
  3. ^ Fisher, G.L.; Mellor, B. (2007), "Three-dimensional finite point groups and the symmetry of beaded beads" (PDF), Journal for Mathematics and the Arts 
  4. ^ Radaelli, Paolo G., Fundamentals of Crystallographic Symmetry (PDF) 
  5. ^ Hitzer, E.S.M.; Ichikawa, D. (2008), "Representation of crystallographic subperiodic groups by geometric algebra" (PDF), Electronic Proc. of AGACSE (Leipzig, Germany) (3, 17–19 Aug. 2008) 

External links[edit]