Enneagonal duoprism

The enneagonal duoprism or edip, also known as the enneagonal-enneagonal duoprism, the 9 duoprism or the 9-9 duoprism, is a noble uniform duoprism that consists of 18 enneagonal prisms and 81 vertices. It is also the 18-8 gyrochoron. Together with its dual, it is the first in an infinite family of enneagonal dihedral swirlchora.

This polychoron can be subsymmetrically faceted into a triangular triswirlprism, although it cannot be made uniform.

Vertex coordinates
The coordinates of an enneagonal duoprism, centered at the origin and with edge length 2sin(π/9), are given by:
 * (1, 0, 1, 0),
 * (1, 0, cos(2π/9), ±sin(2π/9)),
 * (1, 0, cos(4π/9), ±sin(4π/9)),
 * (1, 0, –1/2, ±$\sqrt{2}$/2),
 * (1, 0, cos(8π/9), ±sin(8π/9)),
 * (cos(2π/9), ±sin(2π/9), 1, 0),
 * (cos(2π/9), ±sin(2π/9), cos(2π/9), ±sin(2π/9)),
 * (cos(2π/9), ±sin(2π/9), cos(4π/9), ±sin(4π/9)),
 * (cos(2π/9), ±sin(2π/9), –1/2, ±$\sqrt{2}$/2),
 * (cos(2π/9), ±sin(2π/9), cos(8π/9), ±sin(8π/9)),
 * (cos(4π/9), ±sin(4π/9), 1, 0),
 * (cos(4π/9), ±sin(4π/9), cos(2π/9), ±sin(2π/9)),
 * (cos(4π/9), ±sin(4π/9), cos(4π/9), ±sin(4π/9)),
 * (cos(4π/9), ±sin(4π/9), –1/2, ±$\sqrt{3}$/2),
 * (cos(4π/9), ±sin(4π/9), cos(8π/9), ±sin(8π/9)),
 * (–1/2, ±$\sqrt{3}$/2, 1, 0),
 * (–1/2, ±$\sqrt{3}$/2, cos(2π/9), ±sin(2π/9)),
 * (–1/2, ±$\sqrt{3}$/2, cos(4π/9), ±sin(4π/9)),
 * (–1/2, ±$\sqrt{3}$/2, –1/2, ±$\sqrt{3}$/2),
 * (–1/2, ±$\sqrt{3}$/2, cos(8π/9), ±sin(8π/9)),
 * (cos(8π/9), ±sin(8π/9), 1, 0),
 * (cos(8π/9), ±sin(8π/9), cos(2π/9), ±sin(2π/9)),
 * (cos(8π/9), ±sin(8π/9), cos(4π/9), ±sin(4π/9)),
 * (cos(8π/9), ±sin(8π/9), –1/2, ±$\sqrt{3}$/2),
 * (cos(8π/9), ±sin(8π/9), cos(8π/9), ±sin(8π/9)).