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Demipenteractic honeycomb
(No image)
Type	Uniform 5-honeycomb
Family	Alternated hypercubic honeycomb
Schläfli symbols	h{4,3,3,3,4} h{4,3,3,3^1,1} ht_0,5{4,3,3,3,4} h{4,3,3,4}h{∞} h{4,3,3^1,1}h{∞} ht_0,4{4,3,3,4}h{∞} h{4,3,4}h{∞}h{∞} h{4,3^1,1}h{∞}h{∞}
Coxeter diagrams	= =
Facets	{3,3,3,4} h{4,3,3,3}
Vertex figure	t₁{3,3,3,4}
Coxeter group	${\tilde {B}}_{5}$ [4,3,3,3^1,1] ${\tilde {D}}_{5}$ [3^1,1,3,3^1,1]

The 5-demicube honeycomb (or demipenteractic honeycomb) is a uniform space-filling tessellation (or honeycomb) in Euclidean 5-space. It is constructed as an alternation of the regular 5-cube honeycomb.

It is the first tessellation in the demihypercube honeycomb family which, with all the next ones, is not regular, being composed of two different types of uniform facets. The 5-cubes become alternated into 5-demicubes h{4,3,3,3} and the alternated vertices create 5-orthoplex {3,3,3,4} facets.

D5 lattice

The vertex arrangement of the 5-demicubic honeycomb is the D₅ lattice which is the densest known sphere packing in 5 dimensions.^[1] The 40 vertices of the rectified 5-orthoplex vertex figure of the 5-demicubic honeycomb reflect the kissing number 40 of this lattice.^[2]

The D⁺
₅ packing (also called D²
₅) can be constructed by the union of two D₅ lattices. The analogous packings form lattices only in even dimensions. The kissing number is 2⁴=16 (2^n-1 for n<8, 240 for n=8, and 2n(n-1) for n>8).^[3]

∪

The D^*
₅^[4] lattice (also called D⁴
₅ and C²
₅) can be constructed by the union of all four 5-demicubic lattices:^[5] It is also the 5-dimensional body centered cubic, the union of two 5-cube honeycombs in dual positions.

∪

=

∪

.

The kissing number of the D^*
₅ lattice is 10 (2n for n≥5) and its Voronoi tessellation is a tritruncated 5-cubic honeycomb, , containing all bitruncated 5-orthoplex, Voronoi cells.^[6]

Symmetry constructions

There are three uniform construction symmetries of this tessellation. Each symmetry can be represented by arrangements of different colors on the 32 5-demicube facets around each vertex.

Coxeter group	Schläfli symbol	Coxeter-Dynkin diagram	Vertex figure Symmetry	Facets/verf
${\tilde {B}}_{5}$ = [3^1,1,3,3,4] = [1⁺,4,3,3,4]	h{4,3,3,3,4}	=	[3,3,3,4]	32: 5-demicube 10: 5-orthoplex
${\tilde {D}}_{5}$ = [3^1,1,3,3^1,1] = [1⁺,4,3,3^1,1]	h{4,3,3,3^1,1}	=	[3^2,1,1]	16+16: 5-demicube 10: 5-orthoplex
2×½ ${\tilde {C}}_{5}$ = [[(4,3,3,3,4,2⁺)]]	ht_0,5{4,3,3,3,4}			16+8+8: 5-demicube 10: 5-orthoplex

Related honeycombs

This honeycomb is one of 20 uniform honeycombs constructed by the ${\tilde {D}}_{5}$ Coxeter group, all but 3 repeated in other families by extended symmetry, seen in the graph symmetry of rings in the Coxeter–Dynkin diagrams. The 20 permutations are listed with its highest extended symmetry relation:

D5 honeycombs
Extended symmetry	Extended diagram	Extended group	Honeycombs
[3^1,1,3,3^1,1]		${\tilde {D}}_{5}$
<[3^1,1,3,3^1,1]> ↔ [3^1,1,3,3,4]	↔	${\tilde {D}}_{5}$ ×2₁ = ${\tilde {B}}_{5}$	, , , , , ,
[[3^1,1,3,3^1,1]]		${\tilde {D}}_{5}$ ×2₂	,
<2[3^1,1,3,3^1,1]> ↔ [4,3,3,3,4]	↔	${\tilde {D}}_{5}$ ×4₁ = ${\tilde {C}}_{5}$	, , , , ,
[<2[3^1,1,3,3^1,1]>] ↔ [[4,3,3,3,4]]	↔	${\tilde {D}}_{5}$ ×8 = ${\tilde {C}}_{5}$ ×2	, ,

References

^ "The Lattice D5".
^ Sphere packings, lattices, and groups, by John Horton Conway, Neil James Alexander Sloane, Eiichi Bannai [1]
^ Conway (1998), p. 119
^ "The Lattice D5".
^ Conway (1998), p. 120
^ Conway (1998), p. 466

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 [2]
- (Paper 24) H.S.M. Coxeter, Regular and Semi-Regular Polytopes III, [Math. Zeit. 200 (1988) 3-45]
Conway JH, Sloane NJH (1998). Sphere Packings, Lattices and Groups (3rd ed.). Springer. ISBN 0-387-98585-9.

External links

v t e Fundamental convex regular and uniform honeycombs in dimensions 2–9
Space	Family	${\tilde {A}}_{n-1}$	${\tilde {C}}_{n-1}$	${\tilde {B}}_{n-1}$	${\tilde {D}}_{n-1}$	${\tilde {G}}_{2}$ / ${\tilde {F}}_{4}$ / ${\tilde {E}}_{n-1}$
E²	Uniform tiling	0_[3]	δ₃	hδ₃	qδ₃	Hexagonal
E³	Uniform convex honeycomb	0_[4]	δ₄	hδ₄	qδ₄
E⁴	Uniform 4-honeycomb	0_[5]	δ₅	hδ₅	qδ₅	24-cell honeycomb
E⁵	Uniform 5-honeycomb	0_[6]	δ₆	hδ₆	qδ₆
E⁶	Uniform 6-honeycomb	0_[7]	δ₇	hδ₇	qδ₇	2₂₂
E⁷	Uniform 7-honeycomb	0_[8]	δ₈	hδ₈	qδ₈	1₃₃ • 3₃₁
E⁸	Uniform 8-honeycomb	0_[9]	δ₉	hδ₉	qδ₉	1₅₂ • 2₅₁ • 5₂₁
E⁹	Uniform 9-honeycomb	0_[10]	δ₁₀	hδ₁₀	qδ₁₀
E¹⁰	Uniform 10-honeycomb	0_[11]	δ₁₁	hδ₁₁	qδ₁₁
E^n-1	Uniform (n-1)-honeycomb	0_[n]	δ_n	hδ_n	qδ_n	1_k2 • 2_k1 • k₂₁