Uniform 8-polytope

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Template:Short description

Graphs of three regular and related uniform polytopes.

8-simplex

Rectified 8-simplex

Truncated 8-simplex

Cantellated 8-simplex

Runcinated 8-simplex

Stericated 8-simplex

Pentellated 8-simplex

Hexicated 8-simplex

Heptellated 8-simplex

8-orthoplex

Rectified 8-orthoplex

Truncated 8-orthoplex

Cantellated 8-orthoplex

Runcinated 8-orthoplex

Hexicated 8-orthoplex

Cantellated 8-cube

Runcinated 8-cube

Stericated 8-cube

Pentellated 8-cube

Hexicated 8-cube

Heptellated 8-cube

8-cube

Rectified 8-cube

Truncated 8-cube

8-demicube

Truncated 8-demicube

Cantellated 8-demicube

Runcinated 8-demicube

Stericated 8-demicube

Pentellated 8-demicube

Hexicated 8-demicube

421

142

241

In eight-dimensional geometry, an eight-dimensional polytope or 8-polytope is a polytope contained by 7-polytope facets. Each 6-polytope ridge being shared by exactly two 7-polytope facets.

A uniform 8-polytope is one which is vertex-transitive, and constructed from uniform 7-polytope facets.

Regular 8-polytopes

Regular 8-polytopes can be represented by the Schläfli symbol {p,q,r,s,t,u,v}, with v {p,q,r,s,t,u} 7-polytope facets around each peak.

There are exactly three such convex regular 8-polytopes:

  1. {3,3,3,3,3,3,3} - 8-simplex
  2. {4,3,3,3,3,3,3} - 8-cube
  3. {3,3,3,3,3,3,4} - 8-orthoplex

There are no nonconvex regular 8-polytopes.

Characteristics

The topology of any given 8-polytope is defined by its Betti numbers and torsion coefficients.[1]

The value of the Euler characteristic used to characterise polyhedra does not generalize usefully to higher dimensions, and is zero for all 8-polytopes, whatever their underlying topology. This inadequacy of the Euler characteristic to reliably distinguish between different topologies in higher dimensions led to the discovery of the more sophisticated Betti numbers.[1]

Similarly, the notion of orientability of a polyhedron is insufficient to characterise the surface twistings of toroidal polytopes, and this led to the use of torsion coefficients.[1]

Uniform 8-polytopes by fundamental Coxeter groups

Uniform 8-polytopes with reflective symmetry can be generated by these four Coxeter groups, represented by permutations of rings of the Coxeter-Dynkin diagrams:

# Coxeter group Forms
1 A8 [37] Template:CDD 135
2 BC8 [4,36] Template:CDD 255
3 D8 [35,1,1] Template:CDD 191 (64 unique)
4 E8 [34,2,1] Template:CDD 255

Selected regular and uniform 8-polytopes from each family include:

  1. Simplex family: A8 [37] - Template:CDD
    • 135 uniform 8-polytopes as permutations of rings in the group diagram, including one regular:
      1. {37} - 8-simplex or ennea-9-tope or enneazetton - Template:CDD
  2. Hypercube/orthoplex family: B8 [4,36] - Template:CDD
  3. Demihypercube D8 family: [35,1,1] - Template:CDD
  4. E-polytope family E8 family: [34,1,1] - Template:CDD

Uniform prismatic forms

There are many uniform prismatic families, including:

The A8 family

The A8 family has symmetry of order 362880 (9 factorial).

There are 135 forms based on all permutations of the Coxeter-Dynkin diagrams with one or more rings. (128+8-1 cases) These are all enumerated below. Bowers-style acronym names are given in parentheses for cross-referencing.

See also a list of 8-simplex polytopes for symmetric Coxeter plane graphs of these polytopes.

The B8 family

The B8 family has symmetry of order 10321920 (8 factorial x 28). There are 255 forms based on all permutations of the Coxeter-Dynkin diagrams with one or more rings.

See also a list of B8 polytopes for symmetric Coxeter plane graphs of these polytopes.

The D8 family

The D8 family has symmetry of order 5,160,960 (8 factorial x 27).

This family has 191 Wythoffian uniform polytopes, from 3x64-1 permutations of the D8 Coxeter-Dynkin diagram with one or more rings. 127 (2x64-1) are repeated from the B8 family and 64 are unique to this family, all listed below.

See list of D8 polytopes for Coxeter plane graphs of these polytopes.

The E8 family

The E8 family has symmetry order 696,729,600.

There are 255 forms based on all permutations of the Coxeter-Dynkin diagrams with one or more rings. Eight forms are shown below, 4 single-ringed, 3 truncations (2 rings), and the final omnitruncation are given below. Bowers-style acronym names are given for cross-referencing.

See also list of E8 polytopes for Coxeter plane graphs of this family.

Regular and uniform honeycombs

Coxeter-Dynkin diagram correspondences between families and higher symmetry within diagrams. Nodes of the same color in each row represent identical mirrors. Black nodes are not active in the correspondence.

There are five fundamental affine Coxeter groups that generate regular and uniform tessellations in 7-space:

# Coxeter group Coxeter diagram Forms
1 A~7 [3[8]] Template:CDD 29
2 C~7 [4,35,4] Template:CDD 135
3 B~7 [4,34,31,1] Template:CDD 191 (64 new)
4 D~7 [31,1,33,31,1] Template:CDD 77 (10 new)
5 E~7 [33,3,1] Template:CDD 143

Regular and uniform tessellations include:

Regular and uniform hyperbolic honeycombs

There are no compact hyperbolic Coxeter groups of rank 8, groups that can generate honeycombs with all finite facets, and a finite vertex figure. However, there are 4 paracompact hyperbolic Coxeter groups of rank 8, each generating uniform honeycombs in 7-space as permutations of rings of the Coxeter diagrams.

P¯7 = [3,3[7]]:
Template:CDD
Q¯7 = [31,1,32,32,1]:
Template:CDD
S¯7 = [4,33,32,1]:
Template:CDD
T¯7 = [33,2,2]:
Template:CDD

References

Template:Reflist

  • T. Gosset: On the Regular and Semi-Regular Figures in Space of n Dimensions, Messenger of Mathematics, Macmillan, 1900
  • A. Boole Stott: Geometrical deduction of semiregular from regular polytopes and space fillings, Verhandelingen of the Koninklijke academy van Wetenschappen width unit Amsterdam, Eerste Sectie 11,1, Amsterdam, 1910
  • H.S.M. Coxeter:
    • H.S.M. Coxeter, M.S. Longuet-Higgins und J.C.P. Miller: Uniform Polyhedra, Philosophical Transactions of the Royal Society of London, Londne, 1954
    • H.S.M. Coxeter, Regular Polytopes, 3rd Edition, Dover New York, 1973
  • Kaleidoscopes: Selected Writings of H.S.M. Coxeter, edited by F. Arthur Sherk, Peter McMullen, Anthony C. Thompson, Asia Ivic Weiss, Wiley-Interscience Publication, 1995, Template:ISBN Wiley::Kaleidoscopes: Selected Writings of H.S.M. Coxeter
    • (Paper 22) H.S.M. Coxeter, Regular and Semi Regular Polytopes I, [Math. Zeit. 46 (1940) 380–407, MR 2,10]
    • (Paper 23) H.S.M. Coxeter, Regular and Semi-Regular Polytopes II, [Math. Zeit. 188 (1985) 559-591]
    • (Paper 24) H.S.M. Coxeter, Regular and Semi-Regular Polytopes III, [Math. Zeit. 200 (1988) 3-45]
  • N.W. Johnson: The Theory of Uniform Polytopes and Honeycombs, Ph.D. Dissertation, University of Toronto, 1966
  • Template:KlitzingPolytopes

Template:Polytopes

  1. 1.0 1.1 1.2 Richeson, D.; Euler's Gem: The Polyhedron Formula and the Birth of Topoplogy, Princeton, 2008.