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The composition of functions is a special case of the composition of relations, sometimes also denoted by . As a result, all properties of composition of relations are true of composition of functions, [2] such as associativity.
In computer science, function composition is an act or mechanism to combine simple functions to build more complicated ones. Like the usual composition of functions in mathematics , the result of each function is passed as the argument of the next, and the result of the last one is the result of the whole.
In calculus, the chain rule is a formula that expresses the derivative of the composition of two differentiable functions f and g in terms of the derivatives of f and g.More precisely, if = is the function such that () = (()) for every x, then the chain rule is, in Lagrange's notation, ′ = ′ (()) ′ (). or, equivalently, ′ = ′ = (′) ′.
The domain of a composition operator can be taken more narrowly, as some Banach space, often consisting of holomorphic functions: for example, some Hardy space or Bergman space. In this case, the composition operator lies in the realm of some functional calculus , such as the holomorphic functional calculus .
Bijective composition: the first function need not be surjective and the second function need not be injective. A function is bijective if it is both injective and surjective. A bijective function is also called a bijection or a one-to-one correspondence (not to be confused with one-to-one function, which refers to injection
Composite function: is formed by the composition of two functions f and g, by mapping x to f (g(x)). Inverse function: is declared by "doing the reverse" of a given function (e.g. arcsine is the inverse of sine). Implicit function: defined implicitly by a relation between the argument(s) and the value.
Examples illustrating the conversion of a function directly into a composition follow: Example 1. [ 7 ] [ 14 ] Suppose ϕ {\displaystyle \phi } is an entire function satisfying the following conditions:
If a function is bijective (and so possesses an inverse function), then negative iterates correspond to function inverses and their compositions. For example, f −1 (x) is the normal inverse of f, while f −2 (x) is the inverse composed with itself, i.e. f −2 (x) = f −1 (f −1 (x)).