8-simplex

Summary

Regular enneazetton
(8-simplex)
8-simplex t0.svg
Orthogonal projection
inside Petrie polygon
Type Regular 8-polytope
Family simplex
Schläfli symbol {3,3,3,3,3,3,3}
Coxeter-Dynkin diagram CDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.png
7-faces 9 7-simplex7-simplex t0.svg
6-faces 36 6-simplex6-simplex t0.svg
5-faces 84 5-simplex5-simplex t0.svg
4-faces 126 5-cell4-simplex t0.svg
Cells 126 tetrahedron3-simplex t0.svg
Faces 84 triangle2-simplex t0.svg
Edges 36
Vertices 9
Vertex figure 7-simplex
Petrie polygon enneagon
Coxeter group A8 [3,3,3,3,3,3,3]
Dual Self-dual
Properties convex

In geometry, an 8-simplex is a self-dual regular 8-polytope. It has 9 vertices, 36 edges, 84 triangle faces, 126 tetrahedral cells, 126 5-cell 4-faces, 84 5-simplex 5-faces, 36 6-simplex 6-faces, and 9 7-simplex 7-faces. Its dihedral angle is cos−1(1/8), or approximately 82.82°.

It can also be called an enneazetton, or ennea-8-tope, as a 9-facetted polytope in eight-dimensions. The name enneazetton is derived from ennea for nine facets in Greek and -zetta for having seven-dimensional facets, and -on.

As a configurationEdit

This configuration matrix represents the 8-simplex. The rows and columns correspond to vertices, edges, faces, cells, 4-faces, 5-faces, 6-faces and 7-faces. The diagonal numbers say how many of each element occur in the whole 8-simplex. The nondiagonal numbers say how many of the column's element occur in or at the row's element. This self-dual simplex's matrix is identical to its 180 degree rotation.[1][2]

 

CoordinatesEdit

The Cartesian coordinates of the vertices of an origin-centered regular enneazetton having edge length 2 are:

 
 
 
 
 
 
 
 

More simply, the vertices of the 8-simplex can be positioned in 9-space as permutations of (0,0,0,0,0,0,0,0,1). This construction is based on facets of the 9-orthoplex.

Another origin-centered construction uses (1,1,1,1,1,1,1,1)/3 and permutations of (1,1,1,1,1,1,1,-11)/12 for edge length √2.

ImagesEdit

orthographic projections
Ak Coxeter plane A8 A7 A6 A5
Graph        
Dihedral symmetry [9] [8] [7] [6]
Ak Coxeter plane A4 A3 A2
Graph      
Dihedral symmetry [5] [4] [3]

Related polytopes and honeycombsEdit

This polytope is a facet in the uniform tessellations: 251, and 521 with respective Coxeter-Dynkin diagrams:

               ,                

This polytope is one of 135 uniform 8-polytopes with A8 symmetry.

A8 polytopes
 
t0  
t1
 
t2
 
t3
 
t01
 
t02
 
t12
 
t03
 
t13
 
t23
 
t04
 
t14
 
t24
 
t34
 
t05
 
t15
 
t25
 
t06
 
t16
 
t07
 
t012
 
t013
 
t023
 
t123
 
t014
 
t024
 
t124
 
t034
 
t134
 
t234
 
t015
 
t025
 
t125
 
t035
 
t135
 
t235
 
t045
 
t145
 
t016
 
t026
 
t126
 
t036
 
t136
 
t046
 
t056
 
t017
 
t027
 
t037
 
t0123
 
t0124
 
t0134
 
t0234
 
t1234
 
t0125
 
t0135
 
t0235
 
t1235
 
t0145
 
t0245
 
t1245
 
t0345
 
t1345
 
t2345
 
t0126
 
t0136
 
t0236
 
t1236
 
t0146
 
t0246
 
t1246
 
t0346
 
t1346
 
t0156
 
t0256
 
t1256
 
t0356
 
t0456
 
t0127
 
t0137
 
t0237
 
t0147
 
t0247
 
t0347
 
t0157
 
t0257
 
t0167
 
t01234
 
t01235
 
t01245
 
t01345
 
t02345
 
t12345
 
t01236
 
t01246
 
t01346
 
t02346
 
t12346
 
t01256
 
t01356
 
t02356
 
t12356
 
t01456
 
t02456
 
t03456
 
t01237
 
t01247
 
t01347
 
t02347
 
t01257
 
t01357
 
t02357
 
t01457
 
t01267
 
t01367
 
t012345
 
t012346
 
t012356
 
t012456
 
t013456
 
t023456
 
t123456
 
t012347
 
t012357
 
t012457
 
t013457
 
t023457
 
t012367
 
t012467
 
t013467
 
t012567
 
t0123456
 
t0123457
 
t0123467
 
t0123567
 
t01234567

ReferencesEdit

  1. ^ Coxeter 1973, §1.8 Configurations
  2. ^ Coxeter, H.S.M. (1991). Regular Complex Polytopes (2nd ed.). Cambridge University Press. p. 117. ISBN 9780521394901.
  • Coxeter, H.S.M.:
    • — (1973). "Table I (iii): Regular Polytopes, three regular polytopes in n-dimensions (n≥5)". Regular Polytopes (3rd ed.). Dover. pp. 296. ISBN 0-486-61480-8.
    • Sherk, F. Arthur; McMullen, Peter; Thompson, Anthony C.; Weiss, Asia Ivic, eds. (1995). Kaleidoscopes: Selected Writings of H.S.M. Coxeter. Wiley. ISBN 978-0-471-01003-6.
      • (Paper 22) — (1940). "Regular and Semi Regular Polytopes I". Math. Zeit. 46: 380–407. doi:10.1007/BF01181449. S2CID 186237114.
      • (Paper 23) — (1985). "Regular and Semi-Regular Polytopes II". Math. Zeit. 188 (4): 559–591. doi:10.1007/BF01161657. S2CID 120429557.
      • (Paper 24) — (1988). "Regular and Semi-Regular Polytopes III". Math. Zeit. 200: 3–45. doi:10.1007/BF01161745. S2CID 186237142.
  • Conway, John H.; Burgiel, Heidi; Goodman-Strass, Chaim (2008). "26. Hemicubes: 1n1". The Symmetries of Things. p. 409. ISBN 978-1-56881-220-5.
  • Johnson, Norman (1991). "Uniform Polytopes" (Manuscript). {{cite journal}}: Cite journal requires |journal= (help)
    • Johnson, N.W. (1966). The Theory of Uniform Polytopes and Honeycombs (PhD). University of Toronto. OCLC 258527038.
  • Klitzing, Richard. "8D uniform polytopes (polyzetta) x3o3o3o3o3o3o3o — ene".

External linksEdit

  • Glossary for hyperspace, George Olshevsky.
  • Polytopes of Various Dimensions
  • Multi-dimensional Glossary
Family An Bn I2(p) / Dn E6 / E7 / E8 / F4 / G2 Hn
Regular polygon Triangle Square p-gon Hexagon Pentagon
Uniform polyhedron Tetrahedron OctahedronCube Demicube DodecahedronIcosahedron
Uniform polychoron Pentachoron 16-cellTesseract Demitesseract 24-cell 120-cell600-cell
Uniform 5-polytope 5-simplex 5-orthoplex5-cube 5-demicube
Uniform 6-polytope 6-simplex 6-orthoplex6-cube 6-demicube 122221
Uniform 7-polytope 7-simplex 7-orthoplex7-cube 7-demicube 132231321
Uniform 8-polytope 8-simplex 8-orthoplex8-cube 8-demicube 142241421
Uniform 9-polytope 9-simplex 9-orthoplex9-cube 9-demicube
Uniform 10-polytope 10-simplex 10-orthoplex10-cube 10-demicube
Uniform n-polytope n-simplex n-orthoplexn-cube n-demicube 1k22k1k21 n-pentagonal polytope
Topics: Polytope familiesRegular polytopeList of regular polytopes and compounds