Small retrosnub icosicosidodecahedron

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Small retrosnub icosicosidodecahedron
Small retrosnub icosicosidodecahedron.png
Type Uniform star polyhedron
Elements F = 112, E = 180
V = 60 (χ = 8)
Faces by sides(40+60){3}+12{5/2}
Coxeter diagram
Wythoff symbol | 3/2 3/2 5/2
Symmetry group Ih, [5,3], *532
Index references U 72, C 91, W 118
Dual polyhedron Small hexagrammic hexecontahedron
Vertex figure Small retrosnub icosicosidodecahedron vertfig.png
(35.5/3)/2
Bowers acronym Sirsid
3D model of a small retrosnub icosicosidodecahedron Small retrosnub icosicosidodecahedron.stl
3D model of a small retrosnub icosicosidodecahedron

In geometry, the small retrosnub icosicosidodecahedron (also known as a retrosnub disicosidodecahedron, small inverted retrosnub icosicosidodecahedron, or retroholosnub icosahedron) is a nonconvex uniform polyhedron, indexed as U72. It has 112 faces (100 triangles and 12 pentagrams), 180 edges, and 60 vertices. [1] It is given a Schläfli symbol sr{⁵/₃,³/₂}.

Contents

The 40 non-snub triangular faces form 20 coplanar pairs, forming star hexagons that are not quite regular. Unlike most snub polyhedra, it has reflection symmetries.

George Olshevsky nicknamed it the yog-sothoth (after the Cthulhu Mythos deity). [2] [3]

Convex hull

Its convex hull is a nonuniform truncated dodecahedron.

Truncated dodecahedron.png
Truncated dodecahedron
Small retrosnub icosicosidodecahedron convex hull.png
Convex hull
Small retrosnub icosicosidodecahedron.png
Small retrosnub icosicosidodecahedron

Cartesian coordinates

Cartesian coordinates for the vertices of a small retrosnub icosicosidodecahedron are all the even permutations of

(±(1-ϕ−α), 0, ±(3−ϕα))
(±(ϕ-1−α), ±2, ±(2ϕ-1−ϕα))
(±(ϕ+1−α), ±2(ϕ-1), ±(1−ϕα))

where ϕ = (1+5)/2 is the golden ratio and α = 3ϕ−2.

See also

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References

  1. Maeder, Roman. "72: small retrosnub icosicosidodecahedron". MathConsult.
  2. Birrell, Robert J. (May 1992). The Yog-sothoth: analysis and construction of the small inverted retrosnub icosicosidodecahedron (M.S.). California State University.
  3. Bowers, Jonathan (2000). "Uniform Polychora" (PDF). In Reza Sarhagi (ed.). Bridges 2000. Bridges Conference. pp. 239–246.