Visually, the torus looks like a doughnut. Informally, we take a rectangleMathworldPlanetmathPlanetmath, identify two edges to form a cylinderPlanetmathPlanetmath, and then identify the two ends of the cylinder to form the torus. Doing this gives us a surface of genus one. It can also be described as the Cartesian product of two circles, that is, S1×S1. The torus can be parameterized in Cartesian coordinatesMathworldPlanetmath by:


with R the major radius and r the minor radius are constant, and s,t[0,2π).

Figure 1: A torus generated with Mathematica 4.1

To create the torus mathematically, we start with the closed subset X=[0,1]×[0,1]2. Let X* be the set with elements:


and also the four-point set


This can be schematically represented in the following diagram.

Diagram 1: The identifications made on I2 to make a torus.

Opposite sides are identified with equal orientations, and the four corners

are identified to one point.

Note that X* is a partitionMathworldPlanetmathPlanetmath of X, where we have identified opposite sides of the square together, and all four corners together. We can then form the quotient topology induced by the quotient map p:XX* by sending each element xX to the corresponding element of X* containing x.

Title torus
Canonical name Torus
Date of creation 2013-03-22 12:55:17
Last modified on 2013-03-22 12:55:17
Owner Daume (40)
Last modified by Daume (40)
Numerical id 15
Author Daume (40)
Entry type Definition
Classification msc 54B15
Classification msc 51H05
Related topic MobiusStrip
Related topic NTorus
Related topic SurfaceOfRevolution2
Defines major radius
Defines minor radius