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geom3d[duality] - define the dual of a given polyhedron
Calling Sequence
duality(dgon, gon, s)
Parameters
dgon
-
the name of the reciprocal polyhedron to be created
core
the given polyhedron (either a regular solid or a semi-regular solid)
s
a sphere which is concentric with the given polyhedron, or a radius of the sphere concentric with the given polyhedron.
Description
The edges and vertices of a polyhedron constitute a special case of a graph, which is a set of N0 points or nodes, joined in pairs by N1 segments or branches. Hence, the essential property of a polyhedron is that its faces together form a single unbounded surface. The edges are merely curves drawn on the surface, which come together in sets of three or more at the vertices. In other words, a polyhedron with N2 faces, N1 edges, and N0 vertices may be regarded as a map, i.e., as the partition of an unbounded surface into N2 polygonal regions by means of N1 simple curves joining pairs of N0 points.
From a given map, one may derive a second, called the dual map, on the same surface. This second map has N2 vertices, one in the interior of each face of the given map; N1 edges, one crossing each edge of the given map; and N0 faces, one surrounding each vertex of the given map. Corresponding to a p-gonal face of the given map, the dual map will have a vertex where p edges (and p faces) come together.
Duality is a symmetric relation: a map is the dual of its dual.
Regular map: a map is said to be regular, of type , if there are p vertices and p edges for each face, q edges and q faces at each vertex, arranged symmetrically in a sense that can be made precise. Thus a regular polyhedron is a special case of a regular map. For each map of type , there is a dual map of type .
Consider the regular polyhedron , with its N0 vertices, N1 edges, N2 faces. If we replace each edge by a perpendicular line touching the mid-sphere at the same point, we obtain the N1 edges of the reciprocal polyhedron , which has N2 vertices and N0 faces. This process is, in fact, reciprocation with respect to the mid-sphere: the vertices and face-planes of are the poles and polars of the face-planes and vertices of . Reciprocation with respect to another concentric sphere would yield a larger or smaller .
This process of reciprocation can evidently be applied to any figure which has a recognizable ``center''. It agrees with the topological duality that one defines for maps. The thirteen Archimedean solids hence are included in this case, i.e., for each Archimedean solid, there exists a reciprocal polyhedron.
For a given regular solid, its dual is also a regular solid. To access information of the dual of an Archimedean solid, use the following function calls:
center(dgon)
returns the center of dgon.
faces(dgon)
returns the faces of dgon, each face is represented
as a list of coordinates of its vertices.
form(dgon)
returns the form of dgon.
radius(dgon)
returns the mid-radius of dgon.
schlafli(dgon)
returns the ``Schlafli'' symbol of dgon.
vertices(dgon)
returns the coordinates of vertices of dgon.
Examples
Define the reciprocal polyhedron of a small stellated dodecahedron with center (0,0,0) radius 1 with respect to its mid-sphere:
Plotting:
Define the reciprocal polyhedron of a small rhombiicosidodecahedron with center (0,0,0) radius 1 with respect to its mid-sphere:
See Also
geom3d[Archimedean], geom3d[polar], geom3d[pole], geom3d[RegularPolyhedron]
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