Compound of twenty octahedra with rotational freedom - Alchetron, the free social encyclopedia

This uniform polyhedron compound is a symmetric arrangement of 20 octahedra, considered as triangular antiprisms. It can be constructed by superimposing two copies of the compound of 10 octahedra UC₁₆, and for each resulting pair of octahedra, rotating each octahedron in the pair by an equal and opposite angle θ.

When θ is zero or 60 degrees, the octahedra coincide in pairs yielding (two superimposed copies of) the compounds of ten octahedra UC₁₆ and UC₁₅ respectively. At a certain intermediate angle, octahedra (from distinct rotational axes) coincide in sets four, yielding the compound of five octahedra. At another intermediate angle the vertices coincide in pairs, yielding the compound of twenty octahedra (without rotational freedom).

Cartesian coordinates

Cartesian coordinates for the vertices of this compound are all the cyclic permutations of

( ± 2 3 sin ⁡ θ , ± ( τ − 1 2 + 2 τ cos ⁡ θ ) , ± ( τ 2 − 2 τ − 1 cos ⁡ θ ) ) ( ± ( 2 − τ 2 cos ⁡ θ + τ − 1 3 sin ⁡ θ ) , ± ( 2 + ( 2 τ − 1 ) cos ⁡ θ + 3 sin ⁡ θ ) , ± ( 2 + τ − 2 cos ⁡ θ − τ 3 sin ⁡ θ ) ) ( ± ( τ − 1 2 − τ cos ⁡ θ − τ 3 sin ⁡ θ ) , ± ( τ 2 + τ − 1 cos ⁡ θ + τ − 1 3 sin ⁡ θ ) , ± ( 3 cos ⁡ θ − 3 sin ⁡ θ ) ) ( ± ( − τ − 1 2 + τ cos ⁡ θ − τ 3 sin ⁡ θ ) , ± ( τ 2 + τ − 1 cos ⁡ θ − τ − 1 3 sin ⁡ θ ) , ± ( 3 cos ⁡ θ + 3 sin ⁡ θ ) ) ( ± ( − 2 + τ 2 cos ⁡ θ + τ − 1 3 sin ⁡ θ ) , ± ( 2 + ( 2 τ − 1 ) cos ⁡ θ − 3 sin ⁡ θ ) , ± ( 2 + τ − 1 cos ⁡ θ + τ 3 sin ⁡ θ ) )

where τ = (1 + √5)/2 is the golden ratio (sometimes written φ).

References

Compound of twenty octahedra with rotational freedom Wikipedia

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