Snub (geometry)
Snub cube or Snub cuboctahedron |
Snub dodecahedron or Snub icosidodecahedron |
In
The terminology was generalized by
Conway snubs
John Conway explored generalized polyhedron operators, defining what is now called Conway polyhedron notation, which can be applied to polyhedra and tilings. Conway calls Coxeter's operation a semi-snub.[2]
In this notation,
Forms to snub | Polyhedra | Euclidean tilings | Hyperbolic tilings | |||
---|---|---|---|---|---|---|
Names | Tetrahedron | Cube or octahedron |
Icosahedron or dodecahedron |
Square tiling | Hexagonal tiling or Triangular tiling |
Heptagonal tiling or Order-7 triangular tiling |
Images | ||||||
Snubbed form Conway notation |
sT | sC = sO | sI = sD | sQ | sH = sΔ | sΔ7 |
Image |
In 4-dimensions, Conway suggests the
Coxeter's snubs, regular and quasiregular
Seed | Rectified r |
Truncated t |
Alternated h | |
---|---|---|---|---|
Name | Cube | Cuboctahedron Rectified cube |
Truncated cuboctahedron Cantitruncated cube |
Snub cuboctahedron Snub rectified cube |
Conway notation | C | CO rC |
tCO trC or trO |
htCO = sCO htrC = srC |
Schläfli symbol | {4,3} | or r{4,3} | or tr{4,3} | htr{4,3} = sr{4,3} |
Coxeter diagram | or | or | or | |
Image |
A regular polyhedron (or tiling), with Schläfli symbol , and
A quasiregular polyhedron, with Schläfli symbol or r{p,q}, and Coxeter diagram or , has quasiregular truncation defined as or tr{p,q}, and or , and has quasiregular snub defined as an alternated truncated rectification or htr{p,q} = sr{p,q}, and or .
For example, Kepler's snub cube is derived from the quasiregular cuboctahedron, with a vertical Schläfli symbol , and
Regular polyhedra with even-order vertices can also be snubbed as alternated truncations, like the snub octahedron, as , , is the alternation of the truncated octahedron, , and . The snub octahedron represents the
The snub tetratetrahedron, as , and , is the alternation of the truncated tetrahedral symmetry form, , and .
Seed | Truncated t |
Alternated h | |
---|---|---|---|
Name | Octahedron | Truncated octahedron | Snub octahedron |
Conway notation | O | tO | htO or sO |
Schläfli symbol | {3,4} | t{3,4} | ht{3,4} = s{3,4} |
Coxeter diagram | |||
Image |
Coxeter's snub operation also allows n-antiprisms to be defined as or , based on n-prisms or , while is a regular n-hosohedron, a degenerate polyhedron, but a valid tiling on the sphere with digon or lune-shaped faces.
Image | ||||||||
---|---|---|---|---|---|---|---|---|
Coxeter
diagrams |
... ... |
|||||||
Schläfli symbols |
s{2,4} | s{2,6} | s{2,8} | s{2,10} | s{2,12} | s{2,14} | s{2,16} ...
|
s{2,∞} |
sr{2,2} |
sr{2,3} |
sr{2,4} |
sr{2,5} |
sr{2,6} |
sr{2,7} |
sr{2,8}... ... |
sr{2,∞} | |
Conway notation |
A2 = T | A3 = O | A4 | A5 | A6 | A7 | A8... | A∞ |
The same process applies for snub tilings:
Triangular tiling Δ |
Truncated triangular tiling tΔ |
Snub triangular tiling htΔ = sΔ |
---|---|---|
{3,6} | t{3,6} | ht{3,6} = s{3,6} |
Examples
Space | Spherical | Euclidean | Hyperbolic | |||||
---|---|---|---|---|---|---|---|---|
Image | ||||||||
Coxeter
diagram |
... | |||||||
Schläfli symbol |
s{2,4} | s{3,4} | s{4,4} | s{5,4} | s{6,4} | s{7,4} | s{8,4} | ...s{∞,4} |
Conway notation |
Spherical | Euclidean | Hyperbolic | |||||
---|---|---|---|---|---|---|---|---|
Image | ||||||||
Coxeter
diagram |
... | |||||||
Schläfli symbol |
sr{2,3} | sr{3,3} | sr{4,3} | sr{5,3} | sr{6,3}
|
sr{7,3}
|
sr{8,3}
|
...sr{∞,3} |
Conway notation |
A3 | sT | sC or sO | sD or sI | sΗ or sΔ |
Space | Spherical | Euclidean | Hyperbolic | |||||
---|---|---|---|---|---|---|---|---|
Image | ||||||||
Coxeter
diagram |
... | |||||||
Schläfli symbol |
sr{2,4} | sr{3,4} | sr{4,4} | sr{5,4} | sr{6,4} | sr{7,4} | sr{8,4} | ... sr{∞,4}
|
Conway notation |
A4 | sC or sO | sQ |
Nonuniform snub polyhedra
Nonuniform polyhedra with all even-valance vertices can be snubbed, including some infinite sets; for example:
Snub square bipyramid |
---|
Snub hexagonal bipyramid |
Image | ... | |||
---|---|---|---|---|
Schläfli symbols |
ss{2,4} | ss{2,6} | ss{2,8} | ss{2,10}... |
ssr{2,2} |
ssr{2,3} |
ssr{2,4} |
ssr{2,5}... |
Coxeter's uniform snub star-polyhedra
Snub star-polyhedra are constructed by their Schwarz triangle (p q r), with rational ordered mirror-angles, and all mirrors active and alternated.
s{3/2,3/2} |
s{(3,3,5/2)} |
sr{5,5/2} |
s{(3,5,5/3)} |
sr{5/2,3} |
sr{5/3,5} |
s{(5/2,5/3,3)} |
sr{5/3,3} |
s{(3/2,3/2,5/2)} |
s{3/2,5/3} |
Coxeter's higher-dimensional snubbed polytopes and honeycombs
In general, a regular polychoron with Schläfli symbol , and
A rectified polychoron = r{p,q,r}, and has snub symbol = sr{p,q,r}, and .
Examples
There is only one uniform convex snub in 4-dimensions, the snub 24-cell. The regular 24-cell has Schläfli symbol, , and
The related snub 24-cell honeycomb can be seen as a or s{3,4,3,3}, and , and lower symmetry or sr{3,3,4,3} and or , and lowest symmetry form as or s{31,1,1,1} and .
A Euclidean honeycomb is an
Another Euclidean (scaliform) honeycomb is an
The only uniform snub hyperbolic uniform honeycomb is the snub hexagonal tiling honeycomb, as s{3,6,3} and , which can also be constructed as an alternated hexagonal tiling honeycomb, h{6,3,3}, . It is also constructed as s{3[3,3]} and .
Another hyperbolic (scaliform) honeycomb is a
See also
Seed | Truncation | Rectification | Bitruncation | Dual | Expansion | Omnitruncation | Alternations | ||
---|---|---|---|---|---|---|---|---|---|
t0{p,q} {p,q} |
t01{p,q} t{p,q} |
t1{p,q} r{p,q} |
t12{p,q} 2t{p,q} |
t2{p,q} 2r{p,q} |
t02{p,q} rr{p,q} |
t012{p,q} tr{p,q} |
ht0{p,q} h{q,p} |
ht12{p,q} s{q,p} |
ht012{p,q} sr{p,q} |
References
- S2CID 202575183.
- ISBN 0-486-61480-8(pp. 154–156 8.6 Partial truncation, or alternation)
- 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,
- (Paper 17) Coxeter, The Evolution of Coxeter–Dynkin diagrams, [Nieuw Archief voor Wiskunde 9 (1991) 233–248]
- (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]
- ISBN 978-0-486-40919-1(Chapter 3: Wythoff's Construction for Uniform Polytopes)
- Norman Johnson Uniform Polytopes, Manuscript (1991)
- N.W. Johnson: The Theory of Uniform Polytopes and Honeycombs, Ph.D. Dissertation, University of Toronto, 1966
- ISBN 978-1-56881-220-5
- Weisstein, Eric W. "Snubification". MathWorld.
- Richard Klitzing, Snubs, alternated facetings, and Stott–Coxeter–Dynkin diagrams, Symmetry: Culture and Science, Vol. 21, No.4, 329–344, (2010) [3]