**Kevin D. Cole**

- the differential equation (Heat, Laplace, Helmoltz),
- the coordinate system (rectangular, cylindrical spherical),
- the body shape, and
- the type of boundary conditions.

Within each coordinate system the body shape is determined by the location of the boundaries, with each boundary defined by a constant value of one coordinate; these are called orthogonal bodies. Several body shapes are listed below for each coordinate system:

- Rectangular: infinite body, semi-infinite body, infinite strip, semi-infinite strip, plate, rectangle, parallelpiped.
- Cylindrical: solid cylinder, hollow cylinder, finite cylinder, infinite region surrounding a circular hole, thin ring, wedge.
- Spherical (polar): infinite body, sphere, hollow sphere, infinite region surrounding a spherical void, spherical sector.