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# Function space

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 Title: Function space Author: World Heritage Encyclopedia Language: English Subject: Collection: Topology of Function Spaces Publisher: World Heritage Encyclopedia Publication Date:

### Function space

In mathematics, a function space is a set of functions of a given kind from a set X to a set Y. It is called a space because in many applications it is a topological space (including metric spaces), a vector space, or both. Namely, if Y is a field, functions have inherent vector structure with two operations of pointwise addition and multiplication to a scalar. Topological and metrical structures of function spaces are more diverse.

## Contents

• Examples 1
• Functional analysis 2
• Norm 3
• Bibliography 4
• See also 5
• Footnotes 6

## Examples

Function spaces appear in various areas of mathematics:

• In set theory, the set of functions from X to Y may be denoted XY or YX.
• As a special case, the power set of a set X may be identified with the set of all functions from X to {0, 1}, denoted 2X.
• The set of bijections from X to Y is denoted XY. The factorial notation X! may be used for permutations of a single set X.
• In linear algebra the set of all linear transformations from a vector space V to another one, W, over the same field, is itself a vector space (with the natural definitions of 'addition of functions' and 'multiplication of functions by scalars' : this vector space is also over the same field as that of V and W.);

## Functional analysis

topological vector spaces within reach of the ideas that would apply to normed spaces of finite dimension.

## Norm

If y is an element of the function space \mathcal {C}(a,b) of all continuous functions that are defined on a closed interval [a,b], the norm \|y\|_\infty defined on \mathcal {C}(a,b) is the maximum absolute value of y (x) for axb,[1]

\| y \| \equiv \max_{a \le x \le b} |y(x)| \qquad \text{where} \ \ y \in \mathcal {C}(a,b) \, .

## Bibliography

• Kolmogorov, A. N., & Fomin, S. V. (1967). Elements of the theory of functions and functional analysis. Courier Dover Publications.
• Stein, Elias; Shakarchi, R. (2011). Functional Analysis: An Introduction to Further Topics in Analysis. Princeton University Press.

## Footnotes

1. ^
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