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Polytope compound

From Wikipedia, the free encyclopedia

A polyhedral compound is a figure that is composed of several polyhedra sharing a common centre. They are the three-dimensional analogs of polygonal compounds such as the hexagram.

The outer vertices of a compound can be connected to form a convex polyhedron called its convex hull. A compound is a facetting of its convex hull.

Another convex polyhedron is formed by the small central space common to all members of the compound. This polyhedron can be used as the core for a set of stellations.

Regular compounds

A regular polyhedral compound can be defined as a compound which, like a regular polyhedron, is vertex-transitive, edge-transitive, and face-transitive. There are five regular compounds of polyhedra:

Regular compound
(Coxeter symbol)
Picture Spherical Convex hull Common core Symmetry group Subgroup
restricting
to one
constituent
Dual-regular compound
Two tetrahedra
{4,3}[2{3,3}]{3,4}
Compound of two tetrahedra.png
Spherical compound of two tetrahedra.png
Cube

[1]

Octahedron *432
[4,3]
Oh
*332
[3,3]
Td
Two tetrahedra
Five tetrahedra
{5,3}[5{3,3}]{3,5}
Compound of five tetrahedra.png
Spherical compound of five tetrahedra.png
Dodecahedron

[1]

Icosahedron

[1]

532
[5,3]+
I
332
[3,3]+
T
Chiral twin
(Enantiomorph)
Ten tetrahedra
2{5,3}[10{3,3}]2{3,5}
Compound of ten tetrahedra.png
Spherical compound of ten tetrahedra.png
Dodecahedron

[1]

Icosahedron *532
[5,3]
Ih
332
[3,3]
T
Ten tetrahedra
Five cubes
2{5,3}[5{4,3}]
Compound of five cubes.png
Spherical compound of five cubes.png
Dodecahedron

[1]

Rhombic triacontahedron

[1]

*532
[5,3]
Ih
3*2
[3,3]
Th
Five octahedra
Five octahedra
[5{3,4}]2{3,5}
Compound of five octahedra.png
Spherical compound of five octahedra.png
Icosidodecahedron

[1]

Icosahedron

[1]

*532
[5,3]
Ih
3*2
[3,3]
Th
Five cubes

Best known is the regular compound of two tetrahedra, often called the stella octangula, a name given to it by Kepler. The vertices of the two tetrahedra define a cube, and the intersection of the two define a regular octahedron, which shares the same face-planes as the compound. Thus the compound of two tetrahedra is a stellation of the octahedron, and in fact, the only finite stellation thereof.

The regular compound of five tetrahedra comes in two enantiomorphic versions, which together make up the regular compound of ten tetrahedra.[1] The regular compound of ten tetrahedra can also be constructed with five Stellae octangulae.[1]

Each of the regular tetrahedral compounds is self-dual or dual to its chiral twin; the regular compound of five cubes and the regular compound of five octahedra are dual to each other.

Hence, regular polyhedral compounds can also be regarded as dual-regular compounds.

Coxeter's notation for regular compounds is given in the table above, incorporating Schläfli symbols. The material inside the square brackets, [d{p,q}], denotes the components of the compound: d separate {p,q}'s. The material before the square brackets denotes the vertex arrangement of the compound: c{m,n}[d{p,q}] is a compound of d {p,q}'s sharing the vertices of {m,n} counted c times. The material after the square brackets denotes the facet arrangement of the compound: [d{p,q}]e{s,t} is a compound of d {p,q}'s sharing the faces of {s,t} counted e times. These may be combined: thus c{m,n}[d{p,q}]e{s,t} is a compound of d {p,q}'s sharing the vertices of {m,n} counted c times and the faces of {s,t} counted e times. This notation can be generalised to compounds in any number of dimensions.[2]

Dual compounds

A dual compound is composed of a polyhedron and its dual, arranged reciprocally about a common intersphere or midsphere, such that the edge of one polyhedron intersects the dual edge of the dual polyhedron. There are five dual compounds of the regular polyhedra.

The core is the rectification of both solids. The hull is the dual of this rectification, and its rhombic faces have the intersecting edges of the two solids as diagonals (and have their four alternate vertices). For the convex solids, this is the convex hull.

Dual compound Picture Hull Core Symmetry group
Two tetrahedra
(Compound of two tetrahedra, stellated octahedron)
Dual compound 4 max.png
Cube Octahedron *432
[4,3]
Oh
Cube-octahedron
(Compound of cube and octahedron)
Dual compound 8 max.png
Rhombic dodecahedron Cuboctahedron *432
[4,3]
Oh
Dodecahedron-icosahedron
(Compound of dodecahedron and icosahedron)
Dual compound 20 max.png
Rhombic triacontahedron Icosidodecahedron *532
[5,3]
Ih
Small stellated dodecahedron-great dodecahedron
(Compound of sD and gD)
Skeleton pair Gr12 and dual, size m (crop), thick.png
Medial rhombic triacontahedron
(Convex: Icosahedron)
Dodecadodecahedron
(Convex: Dodecahedron)
*532
[5,3]
Ih
Great icosahedron-great stellated dodecahedron
(Compound of gI and gsD)
Skeleton pair Gr20 and dual, size s, thick.png
Great rhombic triacontahedron
(Convex: Dodecahedron)
Great icosidodecahedron
(Convex: Icosahedron)
*532
[5,3]
Ih

The tetrahedron is self-dual, so the dual compound of a tetrahedron with its dual is the regular stellated octahedron.

The octahedral and icosahedral dual compounds are the first stellations of the cuboctahedron and icosidodecahedron, respectively.

Uniform compounds

In 1976 John Skilling published Uniform Compounds of Uniform Polyhedra which enumerated 75 compounds (including 6 as infinite prismatic sets of compounds, #20-#25) made from uniform polyhedra with rotational symmetry. (Every vertex is vertex-transitive and every vertex is transitive with every other vertex.) This list includes the five regular compounds above. [1]

The 75 uniform compounds are listed in the Table below. Most are shown singularly colored by each polyhedron element. Some chiral pairs of face groups are colored by symmetry of the faces within each polyhedron.

  • 1-19: Miscellaneous (4,5,6,9,17 are the 5 regular compounds)
UC01-6 tetrahedra.png
UC02-12 tetrahedra.png
UC03-6 tetrahedra.png
UC04-2 tetrahedra.png
UC05-5 tetrahedra.png
UC06-10 tetrahedra.png
UC07-6 cubes.png
UC08-3 cubes.png
UC09-5 cubes.png
UC10-4 octahedra.png
UC11-8 octahedra.png
UC12-4 octahedra.png
UC13-20 octahedra.png
UC14-20 octahedra.png
UC15-10 octahedra.png
UC16-10 octahedra.png
UC17-5 octahedra.png
UC18-5 tetrahemihexahedron.png
UC19-20 tetrahemihexahedron.png
UC20-2k n-m-gonal prisms.png
UC21-k n-m-gonal prisms.png
UC22-2k n-m-gonal antiprisms.png
UC23-k n-m-gonal antiprisms.png
UC24-2k n-m-gonal antiprisms.png
UC25-k n-m-gonal antiprisms.png
UC26-12 pentagonal antiprisms.png
UC27-6 pentagonal antiprisms.png
UC28-12 pentagrammic crossed antiprisms.png
UC29-6 pentagrammic crossed antiprisms.png
UC30-4 triangular prisms.png
UC31-8 triangular prisms.png
UC32-10 triangular prisms.png
UC33-20 triangular prisms.png
UC34-6 pentagonal prisms.png
UC35-12 pentagonal prisms.png
UC36-6 pentagrammic prisms.png
UC37-12 pentagrammic prisms.png
UC38-4 hexagonal prisms.png
UC39-10 hexagonal prisms.png
UC40-6 decagonal prisms.png
UC41-6 decagrammic prisms.png
UC42-3 square antiprisms.png
UC43-6 square antiprisms.png
UC44-6 pentagrammic antiprisms.png
UC45-12 pentagrammic antiprisms.png
  • 46-67: Tetrahedral symmetry embedded in octahedral or icosahedral symmetry,
UC46-2 icosahedra.png
UC47-5 icosahedra.png
UC48-2 great dodecahedra.png
UC49-5 great dodecahedra.png
UC50-2 small stellated dodecahedra.png
UC51-5 small stellated dodecahedra.png
UC52-2 great icosahedra.png
UC53-5 great icosahedra.png
UC54-2 truncated tetrahedra.png
UC55-5 truncated tetrahedra.png
UC56-10 truncated tetrahedra.png
UC57-5 truncated cubes.png
UC58-5 quasitruncated hexahedra.png
UC59-5 cuboctahedra.png
UC60-5 cubohemioctahedra.png
UC61-5 octahemioctahedra.png
UC62-5 rhombicuboctahedra.png
UC63-5 small rhombihexahedra.png
UC64-5 small cubicuboctahedra.png
UC65-5 great cubicuboctahedra.png
UC66-5 great rhombihexahedra.png
UC67-5 great rhombicuboctahedra.png
UC68-2 snub cubes.png
UC69-2 snub dodecahedra.png
UC70-2 great snub icosidodecahedra.png
UC71-2 great inverted snub icosidodecahedra.png
UC72-2 great retrosnub icosidodecahedra.png
UC73-2 snub dodecadodecahedra.png
UC74-2 inverted snub dodecadodecahedra.png
UC75-2 snub icosidodecadodecahedra.png

Other compounds

Compound of 4 cubes.png
Compound of 4 octahedra.png
The compound of four cubes (left) is neither a regular compound, nor a dual compound, nor a uniform compound. Its dual, the compound of four octahedra (right), is a uniform compound.

Two polyhedra that are compounds but have their elements rigidly locked into place are the small complex icosidodecahedron (compound of icosahedron and great dodecahedron) and the great complex icosidodecahedron (compound of small stellated dodecahedron and great icosahedron). If the definition of a uniform polyhedron is generalised they are uniform.

The section for entianomorphic pairs in Skilling's list does not contain the compound of two great snub dodecicosidodecahedra, as the pentagram faces would coincide. Removing the coincident faces results in the compound of twenty octahedra.

4-polytope compounds

Orthogonal projections
Regular compound 75 tesseracts.png
Regular compound 75 16-cells.png
75 {4,3,3} 75 {3,3,4}

In 4-dimensions, there are a large number of regular compounds of regular polytopes. Coxeter lists a few of these in his book Regular Polytopes[3]. McMullen added six in his paper New Regular Compounds of 4-Polytopes[4].

Self-duals:

Compound Constituent Symmetry
120 5-cells 5-cell [5,3,3], order 14400[3]
120 5-cells(var) 5-cell order 1200[4]
720 5-cells 5-cell [5,3,3], order 14400[3]
5 24-cells 24-cell [5,3,3], order 14400[3]

Dual pairs:

Compound 1 Compound 2 Symmetry
3 16-cells[5] 3 tesseracts [3,4,3], order 1152[3]
15 16-cells 15 tesseracts [5,3,3], order 14400[3]
75 16-cells 75 tesseracts [5,3,3], order 14400[3]
75 16-cells(var) 75 tesseracts(var) order 600[4]
300 16-cells 300 tesseracts [5,3,3]+, order 7200[3]
600 16-cells 600 tesseracts [5,3,3], order 14400[3]
25 24-cells 25 24-cells [5,3,3], order 14400[3]

Uniform compounds and duals with convex 4-polytopes:

Compound 1
Vertex-transitive
Compound 2
Cell-transitive
Symmetry
2 16-cells[6] 2 tesseracts [4,3,3], order 384[3]
100 24-cells 100 24-cells [5,3,3]+, order 7200[3]
200 24-cells 200 24-cells [5,3,3], order 14400[3]
5 600-cells 5 120-cells [5,3,3]+, order 7200[3]
10 600-cells 10 120-cells [5,3,3], order 14400[3]
25 24-cells(var) 25 24-cells(var) order 600[4]

The superscript (var) in the tables above indicates that the labeled compounds are distinct from the other compounds with the same number of constituents.

Compounds with regular star 4-polytopes

Self-dual star compounds:

Compound Symmetry
5 {5,5/2,5} [5,3,3]+, order 7200[3]
10 {5,5/2,5} [5,3,3], order 14400[3]
5 {5/2,5,5/2} [5,3,3]+, order 7200[3]
10 {5/2,5,5/2} [5,3,3], order 14400[3]

Dual pairs of compound stars:

Compound 1 Compound 2 Symmetry
5 {3,5,5/2} 5 {5/2,5,3} [5,3,3]+, order 7200
10 {3,5,5/2} 10 {5/2,5,3} [5,3,3], order 14400
5 {5,5/2,3} 5 {3,5/2,5} [5,3,3]+, order 7200
10 {5,5/2,3} 10 {3,5/2,5} [5,3,3], order 14400
5 {5/2,3,5} 5 {5,3,5/2} [5,3,3]+, order 7200
10 {5/2,3,5} 10 {5,3,5/2} [5,3,3], order 14400

Uniform compound stars and duals:

Compound 1
Vertex-transitive
Compound 2
Cell-transitive
Symmetry
5 {3,3,5/2} 5 {5/2,3,3} [5,3,3]+, order 7200
10 {3,3,5/2} 10 {5/2,3,3} [5,3,3], order 14400

Compounds with duals

Dual positions:

Compound Constituent Symmetry
2 5-cell 5-cell [[3,3,3]], order 240
2 24-cell 24-cell [[3,4,3]], order 2304
1 tesseract, 1 16-cell tesseract, 16-cell
1 120-cell, 1 600-cell 120-cell, 600-cell
2 great 120-cell great 120-cell
2 grand stellated 120-cell grand stellated 120-cell
1 icosahedral 120-cell, 1 small stellated 120-cell icosahedral 120-cell, small stellated 120-cell
1 grand 120-cell, 1 great stellated 120-cell grand 120-cell, great stellated 120-cell
1 great grand 120-cell, 1 great icosahedral 120-cell great grand 120-cell, great icosahedral 120-cell
1 great grand stellated 120-cell, 1 grand 600-cell great grand stellated 120-cell, grand 600-cell

Group theory

In terms of group theory, if G is the symmetry group of a polyhedral compound, and the group acts transitively on the polyhedra (so that each polyhedron can be sent to any of the others, as in uniform compounds), then if H is the stabilizer of a single chosen polyhedron, the polyhedra can be identified with the orbit space G/H – the coset gH corresponds to which polyhedron g sends the chosen polyhedron to.

Compounds of tilings

There are eighteen two-parameter families of regular compound tessellations of the Euclidean plane. In the hyperbolic plane, five one-parameter families and seventeen isolated cases are known, but the completeness of this listing has not been enumerated.

The Euclidean and hyperbolic compound families 2 {p,p} (4 ≤ p ≤ ∞, p an integer) are analogous to the spherical stella octangula, 2 {3,3}.

A few examples of Euclidean and hyperbolic regular compounds
Self-dual Duals Self-dual
2 {4,4} 2 {6,3} 2 {3,6} 2 {∞,∞}
Kah 4 4.png
Compound 2 hexagonal tilings.png
Compound 2 triangular tilings.png
Infinite-order apeirogonal tiling and dual.png
3 {6,3} 3 {3,6} 3 {∞,∞}
Compound 3 hexagonal tilings.png
Compound 3 triangular tilings.png
Iii symmetry 000.png

A known family of regular Euclidean compound honeycombs in five or more dimensions is an infinite family of compounds of hypercubic honeycombs, all sharing vertices and faces with another hypercubic honeycomb. This compound can have any number of hypercubic honeycombs.

There are also dual-regular tiling compounds. A simple example is the E2 compound of a hexagonal tiling and its dual triangular tiling, which shares its edges with the deltoidal trihexagonal tiling. The Euclidean compounds of two hypercubic honeycombs are both regular and dual-regular.

Footnotes

  1. ^ a b c d e f g h i j "Compound Polyhedra". www.georgehart.com. Retrieved 2020-09-03.
  2. ^ Coxeter, Harold Scott MacDonald (1973) [1948]. Regular Polytopes (Third ed.). Dover Publications. p. 48. ISBN 0-486-61480-8. OCLC 798003.
  3. ^ a b c d e f g h i j k l m n o p q r s Regular polytopes, Table VII, p. 305
  4. ^ a b c d McMullen, Peter (2018), New Regular Compounds of 4-Polytopes, New Trends in Intuitive Geometry, 27: 307–320
  5. ^ Klitzing, Richard. "Uniform compound stellated icositetrachoron".
  6. ^ Klitzing, Richard. "Uniform compound demidistesseract".

External links

References

  • Skilling, John (1976), "Uniform Compounds of Uniform Polyhedra", Mathematical Proceedings of the Cambridge Philosophical Society, 79: 447–457, doi:10.1017/S0305004100052440, MR 0397554.
  • Cromwell, Peter R. (1997), Polyhedra, Cambridge.
  • Wenninger, Magnus (1983), Dual Models, Cambridge, England: Cambridge University Press, pp. 51–53.
  • Harman, Michael G. (1974), Polyhedral Compounds, unpublished manuscript.
  • Hess, Edmund (1876), "Zugleich Gleicheckigen und Gleichflächigen Polyeder", Schriften der Gesellschaft zur Berörderung der Gasammten Naturwissenschaften zu Marburg, 11: 5–97.
  • Pacioli, Luca (1509), De Divina Proportione.
  • Regular Polytopes, (3rd edition, 1973), Dover edition, ISBN 0-486-61480-8
  • Anthony Pugh (1976). Polyhedra: A visual approach. California: University of California Press Berkeley. ISBN 0-520-03056-7. p. 87 Five regular compounds
  • McMullen, Peter (2018), "New Regular Compounds of 4-Polytopes", New Trends in Intuitive Geometry, 27: 307–320, doi:10.1007/978-3-662-57413-3_12.
This page was last edited on 5 September 2020, at 15:34
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