6-demicube

Demihexeract (6-demicube)
Petrie polygon projection
Type	Uniform 6-polytope
Family	demihypercube
Schläfli symbol	{3,3^3,1} = h{4,3^4} s{2^1,1,1,1,1}
Coxeter diagrams	=
Coxeter symbol	131
5-faces	44	12 {3^1,2,1} 32 {3^4}
4-faces	252	60 {3^1,1,1} 192 {3^3}
Cells	640	160 {3^1,0,1} 480 {3,3}
Faces	640	{3}
Edges	240
Vertices	32
Vertex figure	Rectified 5-simplex
Symmetry group	D6, [3^5,1,1] = [1^+,4,3^4] [2^5]^+
Petrie polygon	decagon
Properties	convex

In geometry, a 6-demicube or demihexteract is a uniform 6-polytope, constructed from a 6-cube (hexeract) with alternated vertices truncated. It is part of a dimensionally infinite family of uniform polytopes called demihypercubes.

E. L. Elte identified it in 1912 as a semiregular polytope, labeling it as HM₆ for a 6-dimensional half measure polytope.

Coxeter named this polytope as 1₃₁ from its Coxeter diagram, with a ring on one of the 1-length branches, . It can named similarly by a 3-dimensional exponential Schläfli symbol $\left\{3 \begin{array}{l}3, 3, 3\\3\end{array}\right\}$ or {3,3^3,1}.

Cartesian coordinates

Cartesian coordinates for the vertices of a demihexeract centered at the origin are alternate halves of the hexeract:

(±1,±1,±1,±1,±1,±1)

with an odd number of plus signs.

Images

orthographic projections

Coxeter plane	B6
Graph
Dihedral symmetry	[12/2]
Coxeter plane	D6	D5
Graph
Dihedral symmetry	[10]	[8]
Coxeter plane	D4	D3
Graph
Dihedral symmetry	[6]	[4]
Coxeter plane	A5	A3
Graph
Dihedral symmetry	[6]	[4]

Related polytopes

There are 47 uniform polytopes with D₆ symmetry, 31 are shared by the B₆ symmetry, and 16 are unique:

D6 polytopes
h{4,3^4}	h2{4,3^4}	h3{4,3^4}	h4{4,3^4}	h5{4,3^4}	h2,3{4,3^4}	h2,4{4,3^4}	h2,5{4,3^4}
h3,4{4,3^4}	h3,5{4,3^4}	h4,5{4,3^4}	h2,3,4{4,3^4}	h2,3,5{4,3^4}	h2,4,5{4,3^4}	h3,4,5{4,3^4}	h2,3,4,5{4,3^4}

The 6-demicube, 1₃₁ is third in a dimensional series of uniform polytopes, expressed by Coxeter as k₃₁ series. The fifth figure is a Euclidean honeycomb, 3₃₁, and the final is a noncompact hyperbolic honeycomb, 4₃₁. Each progressive uniform polytope is constructed from the previous as its vertex figure.

k₃₁ dimensional figures

n	4	5	6	7	8	9
Coxeter group	A3A1	A5	D6	E7	${\tilde{E}}_{7}$ = E7^+	${\bar{T}}_8$=E7^++
Coxeter diagram
Symmetry	[3^−1,3,1]	[3^0,3,1]	[3^1,3,1]	[3^2,3,1]	[3^3,3,1]	[3^4,3,1]
Order	48	720	23,040	2,903,040	∞
Graph					-	-
Name	−131	031	131	231	331	431

It is also the second in a dimensional series of uniform polytopes and honeycombs, expressed by Coxeter as 1_3k series. The next figure is the Euclidean honeycomb 1₃₃ and the final is a noncompact hyperbolic honeycomb, 1₃₄.

1_3k dimensional figures

Space	Finite				Euclidean	Hyperbolic
n	4	5	6	7	8	9
Coxeter group	A3A1	A5	D6	E7	${\tilde{E}}_{7}$=E7^+	${\bar{T}}_8$=E7^++
Coxeter diagram
Symmetry	[3^−1,3,1]	[3^0,3,1]	[3^1,3,1]	[3^2,3,1]	[[3<sup>3,3,1</sup>]]	[3^4,3,1]
Order	48	720	23,040	2,903,040	∞
Graph					-	-
Name	13,-1	130	131	132	133	134

References

• H.S.M. Coxeter:
  • Coxeter, Regular Polytopes, (3rd edition, 1973), Dover edition, ISBN 0-486-61480-8, p.296, Table I (iii): Regular Polytopes, three regular polytopes in n-dimensions (n≥5)
  • H.S.M. Coxeter, Regular Polytopes, 3rd Edition, Dover New York, 1973, p.296, Table I (iii): Regular Polytopes, three regular polytopes in n-dimensions (n≥5)
  • 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, [Math. Zeit. 46 (1940) 380-407, MR 2,10]
    • (Paper 23) H.S.M. Coxeter, Regular and Semi-Regular Polytopes II, [Math. Zeit. 188 (1985) 559-591]
    • (Paper 24) H.S.M. Coxeter, Regular and Semi-Regular Polytopes III, [Math. Zeit. 200 (1988) 3-45]
• John H. Conway, Heidi Burgiel, Chaim Goodman-Strass, The Symmetries of Things 2008, ISBN 978-1-56881-220-5 (Chapter 26. pp. 409: Hemicubes: 1_n1)
• Richard Klitzing, 6D uniform polytopes (polypeta), x3o3o *b3o3o3o – hax

External links

• Olshevsky, George, Demihexeract at Glossary for Hyperspace.
• Multi-dimensional Glossary