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

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

An electronic analog computing device that accepts as input two periodic functions and outputs their mathematical product

(chemistry) The relationship between the acidity of a solution and the concentration of its solute.

(computing) Any function that is provided as part of a high-level language and can be executed by a simple reference with specification of arguments

(mathematics) Any function whose value is unchanged if the independent variable changes sign i.e. f(x) = f(-x)

(mathematics) A function of two, three or n variables which is a solution to any of Laplace's equations

(mathematics) Any function in which an independent variable is in the form of an exponent; they are the inverse functions of logarithms

(mathematics) Any function of a complex variable which is periodic in two directions.

(mathematical analysis, algebraic geometry) A function defined by a (multivariable) implicit equation when one of the variables is regarded as the value of the function, especially where said equation is such that the value is not directly calculable from the other variables.