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7-demicubic honeycomb
(No image)
Type	Uniform 7-honeycomb
Family	Alternated hypercube honeycomb
Schläfli symbol	h{4,3,3,3,3,3,4} h{4,3,3,3,3,3} ht0,7{4,3,3,3,3,3,4}
Coxeter-Dynkin diagram	= =
Facets	{3,3,3,3,3,4} h{4,3,3,3,3,3}
Vertex figure	Rectified 7-orthoplex
Coxeter group	${\displaystyle {\tilde {B}}_{7}}$ ${\displaystyle {\tilde {D}}_{7}}$,

The 7-demicubic honeycomb, or demihepteractic honeycomb is a uniform space-filling tessellation (or honeycomb) in Euclidean 7-space. It is constructed as an alternation of the regular 7-cubic honeycomb.

It is composed of two different types of facets. The 7-cubes become alternated into 7-demicubes h{4,3,3,3,3,3} and the alternated vertices create 7-orthoplex {3,3,3,3,3,4} facets.

D7 lattice

The vertex arrangement of the 7-demicubic honeycomb is the D₇ lattice. The 84 vertices of the rectified 7-orthoplex vertex figure of the 7-demicubic honeycomb reflect the kissing number 84 of this lattice. The best known is 126, from the E₇ lattice and the 3₃₁ honeycomb.

The D
₇ packing (also called D
₇) can be constructed by the union of two D₇ lattices. The D
_n packings form lattices only in even dimensions. The kissing number is 2=64 (2 for n<8, 240 for n=8, and 2n(n-1) for n>8).

∪

The D
₇ lattice (also called D
₇ and C
₇) can be constructed by the union of all four 7-demicubic lattices: 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
₇ lattice is 14 (2n for n≥5) and its Voronoi tessellation is a quadritruncated 7-cubic honeycomb, , containing all with tritruncated 7-orthoplex, Voronoi cells.

Symmetry constructions

There are three uniform construction symmetries of this tessellation. Each symmetry can be represented by arrangements of different colors on the 128 7-demicube facets around each vertex.

Coxeter group	Schläfli symbol	Coxeter-Dynkin diagram	Vertex figure Symmetry	Facets/verf
${\displaystyle {\tilde {B}}_{7}}$ = =	h{4,3,3,3,3,3,4}	=		128: 7-demicube 14: 7-orthoplex
${\displaystyle {\tilde {D}}_{7}}$ = =	h{4,3,3,3,3,3}	=		64+64: 7-demicube 14: 7-orthoplex
2×½${\displaystyle {\tilde {C}}_{7}}$ = ]	ht0,7{4,3,3,3,3,3,4}			64+32+32: 7-demicube 14: 7-orthoplex

See also

• 7-cubic honeycomb

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}={3,4}, 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,
• Conway JH, Sloane NJH (1998). Sphere Packings, Lattices and Groups (3rd ed.). ISBN 0-387-98585-9.

Notes

1. "The Lattice D7".
2. Sphere packings, lattices, and groups, by John Horton Conway, Neil James Alexander Sloane, Eiichi Bannai
3. Conway (1998), p. 119
4. "The Lattice D7".
5. Conway (1998), p. 466

External links

v t e Fundamental convex regular and uniform honeycombs in dimensions 2–9
Space	Family	${\displaystyle {\tilde {A}}_{n-1}}$	${\displaystyle {\tilde {C}}_{n-1}}$	${\displaystyle {\tilde {B}}_{n-1}}$	${\displaystyle {\tilde {D}}_{n-1}}$	${\displaystyle {\tilde {G}}_{2}}$ / ${\displaystyle {\tilde {F}}_{4}}$ / ${\displaystyle {\tilde {E}}_{n-1}}$
E	Uniform tiling	0	δ3	hδ3	qδ3	Hexagonal
E	Uniform convex honeycomb	0	δ4	hδ4	qδ4
E	Uniform 4-honeycomb	0	δ5	hδ5	qδ5	24-cell honeycomb
E	Uniform 5-honeycomb	0	δ6	hδ6	qδ6
E	Uniform 6-honeycomb	0	δ7	hδ7	qδ7	222
E	Uniform 7-honeycomb	0	δ8	hδ8	qδ8	133 • 331
E	Uniform 8-honeycomb	0	δ9	hδ9	qδ9	152 • 251 • 521
E	Uniform 9-honeycomb	0	δ10	hδ10	qδ10
E	Uniform 10-honeycomb	0	δ11	hδ11	qδ11
E	Uniform (n-1)-honeycomb	0	δn	hδn	qδn	1k2 • 2k1 • k21

• Honeycombs (geometry)
• 8-polytopes