8-demicubic honeycomb

8-demicubic honeycomb
(No image)
Type	Uniform 8-space honeycomb
Family	Alternated hypercube honeycomb
Schläfli symbol	h{4,3,3,3,3,3,3,4}
Coxeter-Dynkin diagram	or
Facets	{3,3,3,3,3,3,4} h{4,3,3,3,3,3,3}
Vertex figure	Rectified octacross
Coxeter group	${\tilde{B}}_8$ [4,3,3,3,3,3,3^1,1] ${\tilde{D}}_8$ [3^1,1,3,3,3,3,3^1,1]

The 8-demicubic honeycomb, or demiocteractic honeycomb is a uniform space-filling tessellation (or honeycomb) in Euclidean 8-space. It is constructed as an alternation of the regular 8-cubic honeycomb.

It is composed of two different types of facets. The 8-cubes become alternated into 8-demicubes h{4,3,3,3,3,3,3} and the alternated vertices create 8-orthoplex {3,3,3,3,3,3,4} facets .

D8 lattice

The vertex arrangement of the 8-demicubic honeycomb is the D₈ lattice.^[1] The 112 vertices of the rectified 8-orthoplex vertex figure of the 8-demicubic honeycomb reflect the kissing number 112 of this lattice.^[2] The best known is 240, from the E₈ lattice and the 5₂₁ honeycomb.

${\tilde{E}}_8$ contains ${\tilde{D}}_8$ as a subgroup of index 270.^[3] Both ${\tilde{E}}_8$ and ${\tilde{D}}_8$ can be seen as affine extensions of $D_8$ from different nodes:

The D+
8 lattice (also called D2
8) can be constructed by the union of two D8 lattices. This packing is only a lattice for even dimensions. The kissing number is 240. (2^n-1 for n<8, 240 for n=8, and 2n(n-1) for n>8).^[4] It is identical to the E8 lattice. At 8-dimensions, the 240 contacts contain both the 2⁷=128 from lower dimension contact progression (2^n-1), and 16*7=112 from higher dimensions (2n(n-1)).

∪ = .

The D*
8 lattice (also called D4
8 and C2
8) can be constructed by the union of all four D8 lattices:^[5] It is also the 7-dimensional body centered cubic, the union of two 7-cube honeycombs in dual positions.

∪ ∪ ∪ = ∪ .

The kissing number of the D*
8 lattice is 16 (2n for n≥5).^[6] and its Voronoi tessellation is a quadrirectified 8-cubic honeycomb, , containing all trirectified 8-orthoplex Voronoi cell, .^[7]

See also

• 8-cubic honeycomb
• Uniform polytope

Notes

1. http://www.math.rwth-aachen.de/~Gabriele.Nebe/LATTICES/D8.html
2. Sphere packings, lattices, and groups, by John Horton Conway, Neil James Alexander Sloane, Eiichi Bannai
3. Johnson (2015) p.177
4. Conway (1998), p. 119
5. http://www.math.rwth-aachen.de/~Gabriele.Nebe/LATTICES/Ds8.html
6. Conway (1998), p. 120
7. Conway (1998), p. 466

References

• Coxeter, H.S.M. Regular Polytopes, (3rd edition, 1973), Dover edition, ISBN 0-486-61480-8
  • pp. 154–156: Partial truncation or alternation, represented by h prefix: h{4,4}={4,4}; h{4,3,4}={3^1,1,4}, h{4,3,3,4}={3,3,4,3}, ...
• 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 24) H.S.M. Coxeter, Regular and Semi-Regular Polytopes III, [Math. Zeit. 200 (1988) 3-45]
• N.W. Johnson: Geometries and Transformations, (2015)
• Conway JH, Sloane NJH (1998). Sphere Packings, Lattices and Groups (3rd ed.). ISBN 0-387-98585-9.

External links

• Olshevsky, George, Half measure polytope at Glossary for Hyperspace.