(physics) The relationship between the energy of an electron and its ability to excite an atom to a particular excited state

(mathematics) Any function that is a solution of the Bessel equation

(computing) Any character used to specify a function of a piece of software or hardware (such as carriage return of a printer)

(mathematics) Any function of a complex variable that is holomorphic throughout the complex plane

(mathematics) Any function in which an independent variable appears in the form of a logarithm; they are the inverse functions of exponential functions

Any mathematical relationship between an activity and its cost.

(mathematics) Any function of a real variable whose value decreases (or is constant) as the variable increases.

(physics) The function governing the rate at which mechanical energy is converted to heat during viscous flow.

(mathematics) Any function whose value may be directly calculated from the independent variable.

(mathematics) Any function that is composed of algebraic functions, trigonometric functions, exponential functions and/or logarithmic functions, combined using addition, subtraction, multiplication and/or division