Misplaced Pages

7-simplex honeycomb

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.
(Redirected from A7 lattice) 7-homeycomb
7-simplex honeycomb
(No image)
Type Uniform 7-honeycomb
Family Simplectic honeycomb
Schläfli symbol {3} = 0
Coxeter diagram
6-face types {3} , t1{3}
t2{3} , t3{3}
6-face types {3} , t1{3}
t2{3}
5-face types {3} , t1{3}
t2{3}
4-face types {3} , t1{3}
Cell types {3,3} , t1{3,3}
Face types {3}
Vertex figure t0,6{3}
Symmetry A ~ 7 {\displaystyle {\tilde {A}}_{7}} ×21, <>
Properties vertex-transitive

In seven-dimensional Euclidean geometry, the 7-simplex honeycomb is a space-filling tessellation (or honeycomb). The tessellation fills space by 7-simplex, rectified 7-simplex, birectified 7-simplex, and trirectified 7-simplex facets. These facet types occur in proportions of 2:2:2:1 respectively in the whole honeycomb.

A7 lattice

This vertex arrangement is called the A7 lattice or 7-simplex lattice. The 56 vertices of the expanded 7-simplex vertex figure represent the 56 roots of the A ~ 7 {\displaystyle {\tilde {A}}_{7}} Coxeter group. It is the 7-dimensional case of a simplectic honeycomb. Around each vertex figure are 254 facets: 8+8 7-simplex, 28+28 rectified 7-simplex, 56+56 birectified 7-simplex, 70 trirectified 7-simplex, with the count distribution from the 9th row of Pascal's triangle.

E ~ 7 {\displaystyle {\tilde {E}}_{7}} contains A ~ 7 {\displaystyle {\tilde {A}}_{7}} as a subgroup of index 144. Both E ~ 7 {\displaystyle {\tilde {E}}_{7}} and A ~ 7 {\displaystyle {\tilde {A}}_{7}} can be seen as affine extensions from A 7 {\displaystyle A_{7}} from different nodes:

The A
7 lattice can be constructed as the union of two A7 lattices, and is identical to the E7 lattice.

= .

The A
7 lattice is the union of four A7 lattices, which is identical to the E7* lattice (or E
7).

= + = dual of .

The A
7 lattice (also called A
7) is the union of eight A7 lattices, and has the vertex arrangement to the dual honeycomb of the omnitruncated 7-simplex honeycomb, and therefore the Voronoi cell of this lattice is an omnitruncated 7-simplex.

= dual of .

Related polytopes and honeycombs

This honeycomb is one of 29 unique uniform honeycombs constructed by the A ~ 7 {\displaystyle {\tilde {A}}_{7}} Coxeter group, grouped by their extended symmetry of rings within the regular octagon diagram:

A7 honeycombs
Octagon
symmetry
Extended
symmetry
Extended
diagram
Extended
group
Honeycombs
a1 A ~ 7 {\displaystyle {\tilde {A}}_{7}}

d2 <> A ~ 7 {\displaystyle {\tilde {A}}_{7}} ×21

1

p2 ] A ~ 7 {\displaystyle {\tilde {A}}_{7}} ×22

2

d4 <2> A ~ 7 {\displaystyle {\tilde {A}}_{7}} ×41

p4 ] A ~ 7 {\displaystyle {\tilde {A}}_{7}} ×42

d8 ] A ~ 7 {\displaystyle {\tilde {A}}_{7}} ×8
r16 ] A ~ 7 {\displaystyle {\tilde {A}}_{7}} ×16 3

Projection by folding

The 7-simplex honeycomb can be projected into the 4-dimensional tesseractic honeycomb by a geometric folding operation that maps two pairs of mirrors into each other, sharing the same vertex arrangement:

A ~ 7 {\displaystyle {\tilde {A}}_{7}}
C ~ 4 {\displaystyle {\tilde {C}}_{4}}

See also

Regular and uniform honeycombs in 7-space:

Notes

  1. "The Lattice A7".
  2. N.W. Johnson: Geometries and Transformations, (2018) 12.4: Euclidean Coxeter groups, p.294
  3. Weisstein, Eric W. "Necklace". MathWorld., OEIS sequence A000029 30-1 cases, skipping one with zero marks

References

  • Norman Johnson Uniform Polytopes, Manuscript (1991)
  • 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, ISBN 978-0-471-01003-6
    • (Paper 22) H.S.M. Coxeter, Regular and Semi Regular Polytopes I, (1.9 Uniform space-fillings)
    • (Paper 24) H.S.M. Coxeter, Regular and Semi-Regular Polytopes III,
Fundamental convex regular and uniform honeycombs in dimensions 2–9
Space Family A ~ n 1 {\displaystyle {\tilde {A}}_{n-1}} C ~ n 1 {\displaystyle {\tilde {C}}_{n-1}} B ~ n 1 {\displaystyle {\tilde {B}}_{n-1}} D ~ n 1 {\displaystyle {\tilde {D}}_{n-1}} G ~ 2 {\displaystyle {\tilde {G}}_{2}} / F ~ 4 {\displaystyle {\tilde {F}}_{4}} / E ~ n 1 {\displaystyle {\tilde {E}}_{n-1}}
E Uniform tiling 0 δ3 3 3 Hexagonal
E Uniform convex honeycomb 0 δ4 4 4
E Uniform 4-honeycomb 0 δ5 5 5 24-cell honeycomb
E Uniform 5-honeycomb 0 δ6 6 6
E Uniform 6-honeycomb 0 δ7 7 7 222
E Uniform 7-honeycomb 0 δ8 8 8 133331
E Uniform 8-honeycomb 0 δ9 9 9 152251521
E Uniform 9-honeycomb 0 δ10 10 10
E Uniform 10-honeycomb 0 δ11 11 11
E Uniform (n-1)-honeycomb 0 δn n n 1k22k1k21
Categories: