# 5-demicube

Last updated
Demipenteract
(5-demicube)

Petrie polygon projection
Type Uniform 5-polytope
Family (Dn)5-demicube
Families (En) k21 polytope
1k2 polytope
Coxeter
symbol
121
Schläfli
symbols
{3,32,1} = h{4,33}
s{2,4,3,3} or h{2}h{4,3,3}
sr{2,2,4,3} or h{2}h{2}h{4,3}
h{2}h{2}h{2}h{4}
s{21,1,1,1} or h{2}h{2}h{2}s{2}
Coxeter
diagrams
=

4-faces2610 {31,1,1}
16 {3,3,3}
Cells12040 {31,0,1}
80 {3,3}
Faces160 {3}
Edges80
Vertices16
Vertex
figure

rectified 5-cell
Petrie
polygon
Octagon
Symmetry D5, [32,1,1] = [1+,4,33]
[24]+
Properties convex

In five-dimensional geometry, a demipenteract or 5-demicube is a semiregular 5-polytope, constructed from a 5-hypercube (penteract) with alternated vertices removed.

## Contents

It was discovered by Thorold Gosset. Since it was the only semiregular 5-polytope (made of more than one type of regular facets), he called it a 5-ic semi-regular. E. L. Elte identified it in 1912 as a semiregular polytope, labeling it as HM5 for a 5-dimensional half measure polytope.

Coxeter named this polytope as 121 from its Coxeter diagram, which has branches of length 2, 1 and 1 with a ringed node on one of the short branches, and Schläfli symbol ${\displaystyle \left\{3{\begin{array}{l}3,3\\3\end{array}}\right\}}$ or {3,32,1}.

It exists in the k21 polytope family as 121 with the Gosset polytopes: 221, 321, and 421.

The graph formed by the vertices and edges of the demipenteract is sometimes called the Clebsch graph, though that name sometimes refers to the folded cube graph of order five instead.

## Cartesian coordinates

Cartesian coordinates for the vertices of a demipenteract centered at the origin and edge length 22 are alternate halves of the penteract:

(±1,±1,±1,±1,±1)

with an odd number of plus signs.

## As a configuration

This configuration matrix represents the 5-demicube. The rows and columns correspond to vertices, edges, faces, cells and 4-faces. The diagonal numbers say how many of each element occur in the whole 5-demicube. The nondiagonal numbers say how many of the column's element occur in or at the row's element. [1] [2]

The diagonal f-vector numbers are derived through the Wythoff construction, dividing the full group order of a subgroup order by removing one mirror at a time. [3]

D5k-facefkf0f1f2f3f4k-figurenotes(*)
A4( )f0161030102055 rectified 5-cell D5/A4 = 16*5!/5! = 16
A2A1A1{ }f128063632 triangular prism D5/A2A1A1 = 16*5!/3!/2/2 = 80
A2A1 {3} f2331601221 Isosceles triangle D5/A2A1 = 16*5!/3!/2 = 160
A3A1 h{4,3} f346440*20Segment { }D5/A3A1 = 16*5!/4!/2 = 40
A3 {3,3} 464*8011Segment { }D5/A3 = 16*5!/4! = 80
D4 h{4,3,3} f4824328810*Point ( )D5/D4 = 16*5!/8/4! = 10
A4 {3,3,3} 5101005*16Point ( )D5/A4 = 16*5!/5! = 16

* = The number of elements (diagonal values) can be computed by the symmetry order D5 divided by the symmetry order of the subgroup with selected mirrors removed.

## Projected images

 Perspective projection.

## Images

orthographic projections
Coxeter plane B5
Graph
Dihedral symmetry [10/2]
Coxeter planeD5D4
Graph
Dihedral symmetry[8][6]
Coxeter planeD3A3
Graph
Dihedral symmetry[4][4]

It is a part of a dimensional family of uniform polytopes called demihypercubes for being alternation of the hypercube family.

There are 23 Uniform 5-polytopes (uniform 5-polytopes) that can be constructed from the D5 symmetry of the demipenteract, 8 of which are unique to this family, and 15 are shared within the penteractic family.

D5 polytopes

h{4,3,3,3}

h2{4,3,3,3}

h3{4,3,3,3}

h4{4,3,3,3}

h2,3{4,3,3,3}

h2,4{4,3,3,3}

h3,4{4,3,3,3}

h2,3,4{4,3,3,3}

The 5-demicube is third in a dimensional series of semiregular polytopes. Each progressive uniform polytope is constructed vertex figure of the previous polytope. Thorold Gosset identified this series in 1900 as containing all regular polytope facets, containing all simplexes and orthoplexes (5-simplices and 5-orthoplexes in the case of the 5-demicube). In Coxeter's notation the 5-demicube is given the symbol 121.

k21 figures in n dimensions
SpaceFiniteEuclideanHyperbolic
En 3 4 5 6 7 8 9 10
Coxeter
group
E3=A2A1E4=A4E5=D5 E6 E7 E8 E9 = ${\displaystyle {\tilde {E}}_{8}}$ = E8+E10 = ${\displaystyle {\bar {T}}_{8}}$ = E8++
Coxeter
diagram
Symmetry [3−1,2,1][30,2,1][31,2,1][32,2,1][33,2,1][34,2,1][35,2,1][36,2,1]
Order 121201,92051,8402,903,040696,729,600
Graph --
Name 121 021 121 221 321 421 521 621
1k2 figures in n dimensions
SpaceFiniteEuclideanHyperbolic
n 3 4 5 6 7 8 9 10
Coxeter
group
E3=A2A1E4=A4E5=D5 E6 E7 E8 E9 = ${\displaystyle {\tilde {E}}_{8}}$ = E8+E10 = ${\displaystyle {\bar {T}}_{8}}$ = E8++
Coxeter
diagram
Symmetry
(order)
[3−1,2,1][30,2,1][31,2,1][[32,2,1]][33,2,1][34,2,1][35,2,1][36,2,1]
Order 121201,920103,6802,903,040696,729,600
Graph --
Name 1−1,2 102 112 122 132 142 152 162

## Related Research Articles

In four-dimensional geometry, the rectified 5-cell is a uniform 4-polytope composed of 5 regular tetrahedral and 5 regular octahedral cells. Each edge has one tetrahedron and two octahedra. Each vertex has two tetrahedra and three octahedra. In total it has 30 triangle faces, 30 edges, and 10 vertices. Each vertex is surrounded by 3 octahedra and 2 tetrahedra; the vertex figure is a triangular prism.

In geometry, a five-dimensional polytope is a polytope in five-dimensional space, bounded by (4-polytope) facets, pairs of which share a polyhedral cell.

In eight-dimensional geometry, an eight-dimensional polytope or 8-polytope is a polytope contained by 7-polytope facets. Each 6-polytope ridge being shared by exactly two 7-polytope facets.

In six-dimensional geometry, a uniform 6-polytope is a six-dimensional uniform polytope. A uniform polypeton is vertex-transitive, and all facets are uniform 5-polytopes.

In geometry, demihypercubes (also called n-demicubes, n-hemicubes, and half measure polytopes) are a class of n-polytopes constructed from alternation of an n-hypercube, labeled as n for being half of the hypercube family, γn. Half of the vertices are deleted and new facets are formed. The 2n facets become 2n(n−1)-demicubes, and 2n(n−1)-simplex facets are formed in place of the deleted vertices.

In five-dimensional geometry, a 5-cube is a name for a five-dimensional hypercube with 32 vertices, 80 edges, 80 square faces, 40 cubic cells, and 10 tesseract 4-faces.

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

In geometry, a demihepteract or 7-demicube is a uniform 7-polytope, constructed from the 7-hypercube (hepteract) with alternated vertices removed. It is part of a dimensionally infinite family of uniform polytopes called demihypercubes.

In geometry, a demienneract or 9-demicube is a uniform 9-polytope, constructed from the 9-cube, with alternated vertices removed. It is part of a dimensionally infinite family of uniform polytopes called demihypercubes.

In geometry, a 10-demicube or demidekeract is a uniform 10-polytope, constructed from the 10-cube with alternated vertices removed. It is part of a dimensionally infinite family of uniform polytopes called demihypercubes.

In 6-dimensional geometry, the 221 polytope is a uniform 6-polytope, constructed within the symmetry of the E6 group. It was discovered by Thorold Gosset, published in his 1900 paper. He called it an 6-ic semi-regular figure. It is also called the Schläfli polytope.

In 7-dimensional geometry, the 321 polytope is a uniform 7-polytope, constructed within the symmetry of the E7 group. It was discovered by Thorold Gosset, published in his 1900 paper. He called it an 7-ic semi-regular figure.

In five-dimensional geometry, a rectified 5-cube is a convex uniform 5-polytope, being a rectification of the regular 5-cube.

In geometry of five dimensions or higher, a cantic 5-cube, cantihalf 5-cube, truncated 5-demicube is a uniform 5-polytope, being a truncation of the 5-demicube. It has half the vertices of a cantellated 5-cube.

In six-dimensional geometry, a runcic 5-cube or is a convex uniform 5-polytope. There are 2 runcic forms for the 5-cube. Runcic 5-cubes have half the vertices of runcinated 5-cubes.

In six-dimensional geometry, a runcic 6-cube is a convex uniform 6-polytope. There are 2 unique runcic for the 6-cube.

In six-dimensional geometry, a steric 6-cube is a convex uniform 6-polytope. There are unique 4 steric forms of the 6-cube.

In six-dimensional geometry, a pentic 6-cube is a convex uniform 6-polytope.

In seven-dimensional geometry, a runcic 7-cube is a convex uniform 7-polytope, related to the uniform 7-demicube. There are 2 unique forms.

In five-dimensional geometry, a steric 5-cube or is a convex uniform 5-polytope. There are unique 4 steric forms of the 5-cube. Steric 5-cubes have half the vertices of stericated 5-cubes.

## References

1. Coxeter, Regular Polytopes, sec 1.8 Configurations
2. Coxeter, Complex Regular Polytopes, p.117
3. Klitzing, Richard. "x3o3o *b3o3o - hin".
Family An Bn I2(p) / Dn E6 / E7 / E8 / / Hn
Regular polygon Triangle Square p-gon Hexagon Pentagon
Uniform polyhedron Tetrahedron OctahedronCube Demicube DodecahedronIcosahedron
Uniform polychoron Pentachoron 16-cellTesseract Demitesseract 24-cell 120-cell600-cell
Uniform 5-polytope 5-simplex 5-orthoplex5-cube 5-demicube
Uniform 6-polytope 6-simplex 6-orthoplex6-cube 6-demicube 122221
Uniform 7-polytope 7-simplex 7-orthoplex7-cube 7-demicube 132231321
Uniform 8-polytope 8-simplex 8-orthoplex8-cube 8-demicube 142241421
Uniform 9-polytope 9-simplex 9-orthoplex9-cube 9-demicube
Uniform 10-polytope 10-simplex 10-orthoplex10-cube 10-demicube
Uniform n-polytope n-simplex n-orthoplexn-cube n-demicube 1k22k1k21 n-pentagonal polytope
Topics: Polytope familiesRegular polytopeList of regular polytopes and compounds