In mathematics, and particularly in functional analysis and the Calculus of variations, a functional is a function from a vector space into its underlying scalar field, or a set of functions to the real numbers. In other words, it is a function that takes a vector as its input argument, and returns a scalar. Commonly the vector space is a space of functions, thus the functional takes a function for its input argument, then it is sometimes considered a function of a function. Its use originates in the calculus of variations where one searches for a function that minimizes a certain functional. A particularly important application in physics is searching ...

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  1. A function that takes a function as its argument; More precisely: A function y=f(x) whose argument x varies in a space of (real valued, complex valued) functions and whose value belongs to a monodimensional space. An example: the definite integration of integrable real functions in a real interval.
  2. A scalar-valued linear function on a vector space
  3. An object encapsulating a function pointer (or equivalent).


  1. In good working order.
  2. Useful; serving a purpose, fulfilling a function
    That sculpture is not merely artistic, but also functional: it can be used as a hatrack.
  3. Only for functional purposes, notably in architecture
    ''A functional construction element generally must meet higher technical but lower aesthetical requirements
  4. Having semantics defined purely in terms of mathematical functions, without side-effects.
  5. Of a disease, such that its symptoms cannot be referred to any appreciable lesion or change of structure; opposed to organic disease, in which the organ itself is affected.

The above text is a snippet from Wiktionary: functional
and as such is available under the Creative Commons Attribution/Share-Alike License.

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