Hessian polyhedron

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Hessian polyhedron
Complex polyhedron 3-3-3-3-3.png
Orthographic projection
(triangular 3-edges outlined as black edges)
Schläfli symbol 3{3}3{3}3
Coxeter diagram CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png
Faces27 3{3}3 Complex polygon 3-3-3.png
Edges72 3{} Complex trion.png
Vertices27
Petrie polygon Dodecagon
van Oss polygon 12 3{4}2 Complex polygon 3-4-2.png
Shephard group L3 = 3[3]3[3]3, order 648
Dual polyhedron Self-dual
PropertiesRegular

In geometry, the Hessian polyhedron is a regular complex polyhedron 3{3}3{3}3, CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png, in . It has 27 vertices, 72 3{} edges, and 27 3{3}3 faces. It is self-dual.

Contents

Coxeter named it after Ludwig Otto Hesse for sharing the Hessian configuration or (94123), 9 points lying by threes on twelve lines, with four lines through each point. [1]

Its complex reflection group is 3[3]3[3]3 or CDel 3node.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png, order 648, also called a Hessian group. It has 27 copies of CDel 3node.pngCDel 3.pngCDel 3node.png, order 24, at each vertex. It has 24 order-3 reflections. Its Coxeter number is 12, with degrees of the fundamental invariants 3, 6, and 12, which can be seen in projective symmetry of the polytopes.

The Witting polytope, 3{3}3{3}3{3}3, CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png contains the Hessian polyhedron as cells and vertex figures.

It has a real representation as the 221 polytope, CDel nodes 10r.pngCDel 3ab.pngCDel nodes.pngCDel split2.pngCDel node.pngCDel 3.pngCDel node.png, in 6-dimensional space, sharing the same 27 vertices. The 216 edges in 221 can be seen as the 72 3{} edges represented as 3 simple edges.

Coordinates

Its 27 vertices can be given coordinates in : for (λ, μ = 0,1,2).

(0,ωλ,−ωμ)
(−ωμ,0,ωλ)
(ωλ,−ωμ,0)

where .

As a Configuration

Complex polyhedron 3-3-3-3-3-one-blue-face.png
Hessian polyhedron with triangular 3-edges outlined as black edges, with one face outlined as blue.
Complex polyhedron 3-3-3-3-3-one-blue-van oss polygon.png
One of 12 Van oss polygons, 3{4}2, in the Hessian polyhedron

Its symmetry is given by 3[3]3[3]3 or CDel 3node.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png, order 648. [2]

The configuration matrix for 3{3}3{3}3 is: [3]

The number of k-face elements (f-vectors) can be read down the diagonal. The number of elements of each k-face are in rows below the diagonal. The number of elements of each k-figure are in rows above the diagonal.

L3CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png k-face fkf0f1f2 k-fig Notes
L2CDel node x.pngCDel 2.pngCDel 3node.pngCDel 3.pngCDel 3node.png( )f02788 3{3}3 L3/L2 = 27*4!/4! = 27
L1L1CDel 3node 1.pngCDel 2.pngCDel node x.pngCDel 2.pngCDel 3node.png3{ }f137233{ }L3/L1L1 = 27*4!/9 = 72
L2CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 2.pngCDel node x.png 3{3}3 f28827( )L3/L2 = 27*4!/4! = 27

Images

These are 8 symmetric orthographic projections, some with overlapping vertices, shown by colors. Here the 72 triangular edges are drawn as 3-separate edges.

Coxeter plane orthographic projections
E6
[12]
Aut(E6)
[18/2]
D5
[8]
D4 / A2
[6]
Up 2 21 t0 E6.svg
(1=red,3=orange)
Complex polyhedron 3-3-3-3-3.png
(1)
Up 2 21 t0 D5.svg
(1,3)
Up 2 21 t0 D4.svg
(3,9)
B6
[12/2]
A5
[6]
A4
[5]
A3 / D3
[4]
Up 2 21 t0 B6.svg
(1,3)
Up 2 21 t0 A5.svg
(1,3)
Up 2 21 t0 A4.svg
(1,2)
Up 2 21 t0 D3.svg
(1,4,7)
Double Hessian polyhedron
Schläfli symbol 2{4}3{3}3
Coxeter diagram CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png
Faces72 2{4}3 3-generalized-2-orthoplex skew.svg
Edges216 {} Complex dion.png
Vertices54
Petrie polygon Octadecagon
van Oss polygon {6} Regular polygon 6.svg
Shephard group M3 = 3[3]3[4]2, order 1296
Dual polyhedron Rectified Hessian polyhedron, 3{3}3{4}2
PropertiesRegular

The Hessian polyhedron can be seen as an alternation of CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png, CDel node h.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png = CDel label-33.pngCDel nodes 10ru.pngCDel split2.pngCDel node.pngCDel label3.png. This double Hessian polyhedron has 54 vertices, 216 simple edges, and 72 CDel node 1.pngCDel 4.pngCDel 3node.png faces. Its vertices represent the union of the vertices CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png and its dual CDel 3node.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node 1.png.

Its complex reflection group is 3[3]3[4]2, or CDel 3node.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png, order 1296. It has 54 copies of CDel 3node.pngCDel 3.pngCDel 3node.png, order 24, at each vertex. It has 24 order-3 reflections and 9 order-2 reflections. Its coxeter number is 18, with degrees of the fundamental invariants 6, 12, and 18 which can be seen in projective symmetry of the polytopes.

Coxeter noted that the three complex polytopes CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 3.pngCDel 3node.png, CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png, CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png resemble the real tetrahedron (CDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.png), cube (CDel node 1.pngCDel 4.pngCDel node.pngCDel 3.pngCDel node.png), and octahedron (CDel node 1.pngCDel 3.pngCDel node.pngCDel 4.pngCDel node.png). The Hessian is analogous to the tetrahedron, like the cube is a double tetrahedron, and the octahedron as a rectified tetrahedron. In both sets the vertices of the first belong to two dual pairs of the second, and the vertices of the third are at the center of the edges of the second. [4]

Its real representation 54 vertices are contained by two 221 polytopes in symmetric configurations: CDel nodes 10r.pngCDel 3ab.pngCDel nodes.pngCDel split2.pngCDel node.pngCDel 3.pngCDel node.png and CDel nodes 01r.pngCDel 3ab.pngCDel nodes.pngCDel split2.pngCDel node.pngCDel 3.pngCDel node.png. Its vertices can also be seen in the dual polytope of 122.

Construction

The elements can be seen in a configuration matrix:

M3CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png k-face fkf0f1f2 k-fig Notes
L2CDel node x.pngCDel 2.pngCDel 3node.pngCDel 3.pngCDel 3node.png( )f054883{3}3M3/L2 = 1296/24 = 54
L1A1CDel node 1.pngCDel 2.pngCDel node x.pngCDel 2.pngCDel 3node.png{ }f1221633{ }M3/L1A1 = 1296/6 = 216
M2CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 2.pngCDel node x.png2{4}3f26972( )M3/M2 = 1296/18 = 72

Images

Orthographic projections
Complex polyhedron 2-4-3-3-3.png
CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png polyhedron
Complex polyhedron 2-4-3-3-3 blue-edge.png
CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png polyhedron with one face, 2{4}3 highlighted blue
Complex polyhedron 2-4-3-3-3-bivertexcolor.png
CDel node 1.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png polyhedron with 54 vertices, in two 2 alternate color
Complex polyhedron 3-3-3-4-2-alternated.png
CDel label-33.pngCDel nodes 10ru.pngCDel split2.pngCDel node.pngCDel label3.png and CDel label-33.pngCDel nodes 01rd.pngCDel split2.pngCDel node.pngCDel label3.png, shown here with red and blue vertices form a regular compound CDel node h3.pngCDel 4.pngCDel 3node.pngCDel 3.pngCDel 3node.png

Rectified Hessian polyhedron

Rectified Hessian polyhedron
Schläfli symbol 3{3}3{4}2
Coxeter diagrams CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png
CDel 3node.pngCDel 3.pngCDel 3node 1.pngCDel 3.pngCDel 3node.png or CDel label3.pngCDel node 1.pngCDel split1.pngCDel nodes.pngCDel label-33.png.
Faces54 3{3}3 Complex polygon 3-3-3.png
Edges216 3{} Complex trion.png
Vertices72
Petrie polygon Octadecagon
van Oss polygon 9 3{4}3 Complex polygon 3-4-3.png
Shephard group M3 = 3[3]3[4]2, order 1296
3[3]3[3]3, order 648
Dual polyhedron Double Hessian polyhedron
2{4}3{3}3
PropertiesRegular

The rectification, CDel 3node.pngCDel 3.pngCDel 3node 1.pngCDel 3.pngCDel 3node.png doubles in symmetry as a regular complex polyhedron CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png with 72 vertices, 216 3{} edges, 54 3{3}3 faces. Its vertex figure is 3{4}2, and van oss polygon 3{4}3. It is dual to the double Hessian polyhedron. [5]

It has a real representation as the 122 polytope, CDel nodes.pngCDel 3ab.pngCDel nodes.pngCDel split2.pngCDel node.pngCDel 3.pngCDel node 1.png, sharing the 72 vertices. Its 216 3-edges can be drawn as 648 simple edges, which is 72 less than 122's 720 edges.

Complex polyhedron 3-3-3-4-2.png
CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png or CDel 3node.pngCDel 3.pngCDel 3node 1.pngCDel 3.pngCDel 3node.png has 72 vertices, 216 3-edges, and 54 CDel 3node 1.pngCDel 3.pngCDel 3node.png faces
Complex polyhedron 3-3-3-4-2-one-blue-face.png
CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png with one blue face, CDel 3node 1.pngCDel 3.pngCDel 3node.png highlighted
Complex polyhedron 3-3-3-4-2-one-blue van oss polygon.png
CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png with one of 9 van oss polygon, CDel 3node 1.pngCDel 4.pngCDel 3node.png, 3{4}3, highlighted

Construction

The elements can be seen in two configuration matrices, a regular and quasiregular form.

M3 = 3[3]3[4]2 symmetry
M3CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 4.pngCDel node.png k-face fkf0f1f2 k-fig Notes
CDel node x.pngCDel 2.pngCDel 3node.pngCDel 4.pngCDel node.png( )f072963{4}2M3/M2 = 1296/18 = 72
L1A1CDel 3node 1.pngCDel 2.pngCDel node x.pngCDel 2.pngCDel node.png3{ }f132162{ }M3/L1A1 = 1296/3/2 = 216
L2CDel 3node 1.pngCDel 3.pngCDel 3node.pngCDel 2.pngCDel node x.png3{3}3f28854( )M3/L2 = 1296/24 = 54
L3 = 3[3]3[3]3 symmetry
L3CDel 3node.pngCDel 3.pngCDel 3node 1.pngCDel 3.pngCDel 3node.png k-face fkf0f1f2 k-fig Notes
L1L1CDel 3node.pngCDel 2.pngCDel node x.pngCDel 2.pngCDel 3node.png( )f0729333{ }×3{ }L3/L1L1 = 648/9 = 72
L1CDel node x.pngCDel 2.pngCDel 3node 1.pngCDel 2.pngCDel node x.png3{ }f1321611{ }L3/L1 = 648/3 = 216
L2CDel 3node.pngCDel 3.pngCDel 3node 1.pngCDel 2.pngCDel node x.png3{3}3f28827*( )L3/L2 = 648/24 = 27
CDel node x.pngCDel 2.pngCDel 3node 1.pngCDel 3.pngCDel 3node.png88*27

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References

  1. Coxeter, Complex Regular polytopes, p.123
  2. Coxeter Regular Convex Polytopes, 12.5 The Witting polytope
  3. Coxeter, Complex Regular polytopes, p.132
  4. Coxeter, Complex Regular Polytopes, p.127
  5. Coxeter, H. S. M., Regular Complex Polytopes, second edition, Cambridge University Press, (1991). p.30 and p.47