# Regular toroid

A **regular toroid** is an orientable equivelar polyhedron of genus 1.^{[1]} Despite the name, regular toroids are not necessarily abstractly regular in the standard sense. However, an orientable genus 1 polyhedron that is abstractly regular is a guaranteed regular toroid.

## Classes[edit | edit source]

For polyhedra of genus 1, the Euler characteristic must be 0. Thus

- .

For a regular toroid, if each face has s sides, then the number of faces can be rewritten as . Likewise if the degree of each vertex is d then the number of vertices can be rewritten as . Thus the Euler characteristic can be written as:

Since , this leads to the equation

with the restrictions that and , this leads to 3 solutions:

- ,
- ,
- ,

These three solutions form three classes of regular toroids, called , , and by Lajos Szilassi.^{[1]}

### T_{1} [edit | edit source]

This section needs expansion. You can help by adding to it. |

Regular toroids in the class have six triangular faces meeting at every vertex. They are topologically equivalent to looped portions of the triangular tiling.

### T_{2} [edit | edit source]

Regular toroids in the class have four square faces meeting at every vertex. They have an equal number of faces and vertices. They are topologically equivalent to looped portions of the square tiling.

Constructions are known for regular toroids with n×d faces where both n and d are at least 3. The vertex coordinates of these n -d toroids can be given by where and , and r is the major radius of the torus. The resulting toroid has trapezoidal faces. However there are other numbers of faces for which there exist abstract regular toroids, that do not rule out a realization. For example, it is unknown whether a regular toroid can be constructed with 10 or 11 faces.^{[1]} It is known that no regular toroid has fewer than 9 faces / vertices.^{[1]}

### T_{3} [edit | edit source]

This section needs expansion. You can help by adding to it. |

Regular toroids in the class have 3 hexagonal faces meeting at every vertex. They are topologically equivalent to looped portions of the hexagonal tiling.

## References[edit | edit source]

- ↑
^{1.0}^{1.1}^{1.2}^{1.3}Szilassi, Lajos (1986). "Regular toroids" (PDF).*Structural Topology*.**13**: 69–80.

## External links[edit | edit source]

- Szilassi, Lajos. "On some regular toroids"