isohedral figure

{{short description|≥2-dimensional tessellation or ≥3-dimensional polytope with identical faces}}

{{redirect-distinguish|isohedron|icosahedron}}

{{For|the related Isohedral numbers|Anisohedral tiling}}

File:Dice Set.jpg

In geometry, a tessellation of dimension {{math|2}} (a plane tiling) or higher, or a polytope of dimension {{math|3}} (a polyhedron) or higher, is isohedral or face-transitive if all its faces are the same. More specifically, all faces must be not merely congruent but must be transitive, i.e. must lie within the same symmetry orbit. In other words, for any two faces {{mvar|A}} and {{mvar|B}}, there must be a symmetry of the entire figure by translations, rotations, and/or reflections that maps {{mvar|A}} onto {{mvar|B}}. For this reason, convex isohedral polyhedra are the shapes that will make fair dice.{{citation|title=Dungeons, dragons, and dice|first=K. Robin|last=McLean|journal=The Mathematical Gazette|volume=74|issue=469|year=1990|pages=243–256|doi=10.2307/3619822|jstor=3619822|s2cid=195047512 }}.

Isohedral polyhedra are called isohedra. They can be described by their face configuration. An isohedron has an even number of faces.

The dual of an isohedral polyhedron is vertex-transitive, i.e. isogonal. The Catalan solids, the bipyramids, and the trapezohedra are all isohedral. They are the duals of the (isogonal) Archimedean solids, prisms, and antiprisms, respectively. The Platonic solids, which are either self-dual or dual with another Platonic solid, are vertex-, edge-, and face-transitive (i.e. isogonal, isotoxal, and isohedral).

A form that is isohedral, has regular vertices, and is also edge-transitive (i.e. isotoxal) is said to be a quasiregular dual. Some theorists regard these figures as truly quasiregular because they share the same symmetries, but this is not generally accepted.

A polyhedron which is isohedral and isogonal is said to be noble.

Not all isozonohedra{{Cite web|url=http://mathworld.wolfram.com/Isozonohedron.html|title=Isozonohedron|last=Weisstein|first=Eric W.|website=mathworld.wolfram.com|language=en|access-date=2019-12-26}} are isohedral.{{Cite web|url=http://mathworld.wolfram.com/Isohedron.html|title=Isohedron|last=Weisstein|first=Eric W.|website=mathworld.wolfram.com|language=en|access-date=2019-12-21}} For example, a rhombic icosahedron is an isozonohedron but not an isohedron.{{Cite web|url=http://mathworld.wolfram.com/RhombicIcosahedron.html|title=Rhombic Icosahedron|last=Weisstein|first=Eric W.|website=mathworld.wolfram.com|language=en|access-date=2019-12-21}}

Examples

class="wikitable" style="width:720px;"

!colspan=3|Convex

Concave
valign=top

|180px
Hexagonal bipyramids, V4.4.6, are nonregular isohedral polyhedra.

|240px
The Cairo pentagonal tiling, V3.3.4.3.4, is isohedral.

|240px
The rhombic dodecahedral honeycomb is isohedral (and isochoric, and space-filling).

|240px
A square tiling distorted into a spiraling H tiling (topologically equivalent) is still isohedral.

Classes of isohedra by symmetry

class="wikitable sortable"
Faces||Face
config.
||Class||Name||Symmetry||Order||Convex||Coplanar||Nonconvex
align=center

!4

|V33

Platonictetrahedron
tetragonal disphenoid
rhombic disphenoid

|Td, [3,3], (*332)
D2d, [2+,2], (2*)
D2, [2,2]+, (222)

|24
4
4
4

Image:Tetrahedron.png60px60px
align=center

!6

|V34

Platonic

|cube
trigonal trapezohedron
asymmetric trigonal trapezohedron

|Oh, [4,3], (*432)
D3d, [2+,6]
(2*3)
D3
[2,3]+, (223)

|48
12
12
6

Image:Hexahedron.png30px60px
align=center

!8

|V43

Platonic

|octahedron
square bipyramid
rhombic bipyramid
square scalenohedron

|Oh, [4,3], (*432)
D4h,[2,4],(*224)
D2h,[2,2],(*222)
D2d,[2+,4],(2*2)

|48
16
8
8

Image:Octahedron.png60px60px60px60px60px60px
align=center

!12

|V35

Platonic

|regular dodecahedron
pyritohedron
tetartoid

|Ih, [5,3], (*532)
Th, [3+,4], (3*2)
T, [3,3]+, (*332)

|120
24
12

Image:Dodecahedron.png60px60px60px60px60px60px
align=center

!20

|V53

Platonicregular icosahedron

|Ih, [5,3], (*532)

|120

Image:Icosahedron.png
align=center

! 12

|V3.62

| Catalan

| triakis tetrahedron

|Td, [3,3], (*332)

|24

| Image:triakis tetrahedron.png

60px60px60px
align=center

! 12

|V(3.4)2

| Catalan

| rhombic dodecahedron
deltoidal dodecahedron

|Oh, [4,3], (*432)
Td, [3,3], (*332)

|48
24

| Image:rhombic dodecahedron.png60px60px

60px60px60px
align=center

! 24

|V3.82

| Catalan

| triakis octahedron

|Oh, [4,3], (*432)

|48

| Image:triakis octahedron.png

60px60px
align=center

! 24

|V4.62

| Catalan

| tetrakis hexahedron

|Oh, [4,3], (*432)

|48

| File:Disdyakis cube.png60px

60px60px60px60px
align=center

! 24

|V3.43

| Catalan

| deltoidal icositetrahedron

|Oh, [4,3], (*432)

|48

| Image:Strombic icositetrahedron.png60px

60px60px60px60px
align=center

! 48

|V4.6.8

| Catalan

| disdyakis dodecahedron

|Oh, [4,3], (*432)

|48

| Image:disdyakis dodecahedron.png

60px60px60px60px60px
align=center

! 24

|V34.4

| Catalan

| pentagonal icositetrahedron

|O, [4,3]+, (432)

|24

| Image:pentagonal icositetrahedron.png

align=center

! 30

|V(3.5)2

| Catalan

| rhombic triacontahedron

|Ih, [5,3], (*532)

|120

| Image:rhombic triacontahedron.png

align=center

! 60

|V3.102

| Catalan

| triakis icosahedron

|Ih, [5,3], (*532)

|120

| Image:triakis icosahedron.png

60px60px60px60px
align=center

! 60

|V5.62

| Catalan

| pentakis dodecahedron

|Ih, [5,3], (*532)

|120

| Image:pentakis dodecahedron.png

60px60px60px60px60px
align=center

! 60

|V3.4.5.4

| Catalan

| deltoidal hexecontahedron

|Ih, [5,3], (*532)

|120

| File:Strombic hexecontahedron.png

120px60px
align=center

! 120

|V4.6.10

| Catalan

| disdyakis triacontahedron

|Ih, [5,3], (*532)

|120

| Image:disdyakis triacontahedron.png

60px60px60px60px60px60px
align=center

! 60

|V34.5

| Catalan

| pentagonal hexecontahedron

|I, [5,3]+, (532)

|60

| File:Pentagonal hexecontahedron.png

align=center

!2n

|V33.n

Polar

|trapezohedron
asymmetric trapezohedron

|Dnd, [2+,2n], (2*n)
Dn, [2,n]+, (22n)

|4n
2n

30px60px60px60px
60px60px
align=center

!2n
4n

|V42.n
V42.2n
V42.2n

Polar

|regular n-bipyramid
isotoxal 2n-bipyramid
2n-scalenohedron

|Dnh, [2,n], (*22n)
Dnh, [2,n], (*22n)
Dnd, [2+,2n], (2*n)

|4n

60px60px60px60px60px60px60px60px60px60px60px

''k''-isohedral{{anchor|monohedral}} figure

A polyhedron (or polytope in general) is k-isohedral if it contains k faces within its symmetry fundamental domains.

{{cite journal |last=Socolar |first=Joshua E. S. |year=2007 |title=Hexagonal Parquet Tilings: k-Isohedral Monotiles with Arbitrarily Large k |journal=The Mathematical Intelligencer |volume=29 |issue=2 |pages=33–38 | doi = 10.1007/bf02986203|arxiv=0708.2663 |s2cid=119365079 |url=http://www.phy.duke.edu/~socolar/hexparquet.pdf |access-date=2007-09-09 |format=corrected PDF}} Similarly, a k-isohedral tiling has k separate symmetry orbits (it may contain m different face shapes, for m = k, or only for some m < k).Craig S. Kaplan, [https://books.google.com/books?id=OPtQtnNXRMMC "Introductory Tiling Theory for Computer Graphics"] {{Webarchive|url=https://web.archive.org/web/20221208000331/https://books.google.com/books?id=OPtQtnNXRMMC |date=2022-12-08 }}, 2009, Chapter 5: "Isohedral Tilings", p. 35. ("1-isohedral" is the same as "isohedral".)

A monohedral polyhedron or monohedral tiling (m = 1) has congruent faces, either directly or reflectively, which occur in one or more symmetry positions. An m-hedral polyhedron or tiling has m different face shapes ("dihedral", "trihedral"... are the same as "2-hedral", "3-hedral"... respectively).Tilings and patterns, p. 20, 23.

Here are some examples of k-isohedral polyhedra and tilings, with their faces colored by their k symmetry positions:

class=wikitable width=640

!3-isohedral

!4-isohedral

!isohedral

!2-isohedral

colspan=2|2-hedral regular-faced polyhedra

!colspan=2|Monohedral polyhedra

160px

|160px

|160px

|160px

The rhombicuboctahedron has 1 triangle type and 2 square types.

|The pseudo-rhombicuboctahedron has 1 triangle type and 3 square types.

|The deltoidal icositetrahedron has 1 face type.

|The pseudo-deltoidal icositetrahedron has 2 face types, with same shape.

class=wikitable width=400

!2-isohedral

!4-isohedral

!Isohedral

!3-isohedral

colspan=2|2-hedral regular-faced tilings

!colspan=2|Monohedral tilings

160px

|160px

|160px

|File:P5-type10.png

The Pythagorean tiling has 2 square types (sizes).

|This 3-uniform tiling has 3 triangle types, with same shape, and 1 square type.

|The herringbone pattern has 1 rectangle type.

|This pentagonal tiling has 3 irregular pentagon types, with same shape.

Related terms

A cell-transitive or isochoric figure is an n-polytope (n ≥ 4) or n-honeycomb (n ≥ 3) that has its cells congruent and transitive with each others. In 3 dimensions, the catoptric honeycombs, duals to the uniform honeycombs, are isochoric. In 4 dimensions, isochoric polytopes have been enumerated up to 20 cells.{{cite web | url=http://www.polytope.net/hedrondude/dice4.htm | title=Four Dimensional Dice up to Twenty Sides }}

A facet-transitive or isotopic figure is an n-dimensional polytope or honeycomb with its facets ((n−1)-faces) congruent and transitive. The dual of an isotope is an isogonal polytope. By definition, this isotopic property is common to the duals of the uniform polytopes.

  • An isotopic 2-dimensional figure is isotoxal, i.e. edge-transitive.
  • An isotopic 3-dimensional figure is isohedral, i.e. face-transitive.
  • An isotopic 4-dimensional figure is isochoric, i.e. cell-transitive.

See also

References

{{reflist}}