# Big O notation

## Describes limiting behavior of a function / From Wikipedia, the free encyclopedia

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**Big O notation** is a mathematical notation that describes the limiting behavior of a function when the argument tends towards a particular value or infinity. Big O is a member of a family of notations invented by German mathematicians Paul Bachmann,

^{[1]}Edmund Landau,

^{[2]}and others, collectively called

**Bachmann–Landau notation**or

**asymptotic notation**. The letter O was chosen by Bachmann to stand for

*Ordnung*, meaning the order of approximation.

In computer science, big O notation is used to classify algorithms according to how their run time or space requirements grow as the input size grows.^{[3]} In analytic number theory, big O notation is often used to express a bound on the difference between an arithmetical function and a better understood approximation; a famous example of such a difference is the remainder term in the prime number theorem. Big O notation is also used in many other fields to provide similar estimates.

Big O notation characterizes functions according to their growth rates: different functions with the same asymptotic growth rate may be represented using the same O notation. The letter O is used because the growth rate of a function is also referred to as the **order of the function**. A description of a function in terms of big O notation usually only provides an upper bound on the growth rate of the function.

Associated with big O notation are several related notations, using the symbols *o*, Ω, *ω*, and Θ, to describe other kinds of bounds on asymptotic growth rates.