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, with 4 joining at each vertex. It is also the 18-8 gyrochoron. It is the first in an infinite family of isogonal enneagonal dihedral swirlchora and also the first in an infinite family of isochoric enneagonal hosohedral 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: where j, k = 2, 4, 8.
 * $$\left(1,0,1,0\right),$$
 * $$\left(1,0,\cos\left(\frac{j\pi}9\right),±\sin\left(\frac{j\pi}9\right)\right),$$
 * $$\left(1,0,-\frac12,±\frac{\sqrt3}2\right),$$
 * $$\left(\cos\left(\frac{k\pi}9\right),±\sin\left(\frac{k\pi}9\right),1,0\right),$$
 * $$\left(\cos\left(\frac{k\pi}9\right),±\sin\left(\frac{k\pi}9\right),\cos\left(\frac{j\pi}9\right),±\sin\left(\frac{j\pi}9\right)\right),$$
 * $$\left(\cos\left(\frac{k\pi}9\right),±\sin\left(\frac{k\pi}9\right),-\frac12,±\frac{\sqrt3}2\right),$$
 * $$\left(-\frac12,±\frac{\sqrt3}2,1,0\right),$$
 * $$\left(-\frac12,±\frac{\sqrt3}2,\cos\left(\frac{j\pi}9\right),±\sin\left(\frac{j\pi}9\right)\right),$$
 * $$\left(-\frac12,±\frac{\sqrt3}2,-\frac12,±\frac{\sqrt3}2\right),$$


 * (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, ±$\sqrt{3}$/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)).