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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, ′ = ′ = (′) ′.
In the calculus of relations, the composition of relations is called relative multiplication, [1] and its result is called a relative product. [2]: 40 Function composition is the special case of composition of relations where all relations involved are functions.
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
The Church–Turing thesis is the claim that every philosophically acceptable definition of a computable function defines also the same functions. General recursive functions are partial functions from integers to integers that can be defined from constant functions, successor, and; projection functions; via the operators composition,
If f : X → Y is any function, then f ∘ id X = f = id Y ∘ f, where "∘" denotes function composition. [4] In particular, id X is the identity element of the monoid of all functions from X to X (under function composition). Since the identity element of a monoid is unique, [5] one can alternately define the identity function on M to
As a consequence of Liouville's theorem, any function that is entire on the whole Riemann sphere [d] is constant. Thus any non-constant entire function must have a singularity at the complex point at infinity, either a pole for a polynomial or an essential singularity for a transcendental entire function.