# Big O notation

The **big O notation** is a mathematical notation to express various bounds concerning asymptotic behaviour of functions. It is often used in particular applications in physics, computer science, engineering and other applied sciences. For example, a typical context use in computer science is to express the complexity of algorithms.

More formally, if *f* and *g* are real valued functions of the real variable then the notation indicates that there exist a real number *T* and a constant *C* such that for all

Similarly, if and are two numerical sequences then means that for all *n* big enough.

The big O notation is also often used to indicate that the absolute value of a real valued function around some neighbourhood of a point is upper bounded by a constant multiple of the absolute value of another function, in that neigbourhood. For example, for a real number the notation , where *g*(*t*) is a function which is continuous at *t* = 0 with *g*(0) = 0, denotes that there exists a real positive constant *C* such that on *some* neighbourhood *N* of .