Exercise: Plotting Torus

In geometry, a torus is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle.

A torus is defined by the following equation:

$$x(\theta, \phi)=(R+rcos\theta)cos\phi$$

$$y(\theta, \phi)=(R+rcos\theta)sin\phi$$

$$z(\theta, \phi)=rsin\theta$$