Function of a real variable

In mathematical analysis, and applications in geometry, applied mathematics, engineering, and natural sciences, a function of a real variable is a function whose domain is the real numbers ℝ, more specifically the subset of ℝ for which the function is defined.

The "output", also called the "value of the function", could be anything: simple examples include a single real number, or a vector of real numbers (the function is "vector valued"). Vector-valued functions of a single real variable occur widely in applied mathematics and physics, particularly in classical mechanics of particles, as well as phase paths of dynamical systems. But we could also have a matrix of real numbers as the output (the function is "matrix valued"), and so on. The "output" could also be other number fields, such as complex numbers, quaternions, or even more exotic hypercomplex numbers.

A real-valued function of a real variable is a function that takes as input a real number, commonly represented by the variable x, for producing another real number, the value of the function, commonly denoted f(x). For simplicity, in this article a real-valued function of a real variable will be simply called a function. To avoid any ambiguity, the other types of functions that may occur will be explicitly specified.

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