Dual space

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In mathematics, any vector space, V, has a corresponding dual vector space (or just dual space for short) consisting of all linear functionals on V. Dual vector spaces defined on finite-dimensional vector spaces can be used for defining tensors which are studied in tensor algebra. When applied to vector spaces of functions (which typically are infinite-dimensional), dual spaces are employed for defining and studying concepts like measures, distributions, and Hilbert spaces. Consequently, the dual space is an important concept in the study of functional analysis.

There are two types of dual spaces: the algebraic dual space, and the continuous dual space. The algebraic dual space is defined for all vector spaces. When defined for a topological vector space there is a subspace of this dual space, corresponding to continuous linear functionals, which constitutes a continuous dual space.

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Algebraic dual space

Given any vector space V over a field F, the dual space V* is defined as the set of all linear maps φ: VF (linear functionals). The dual space V* itself becomes a vector space over F when equipped with the following addition and scalar multiplication:

for all φ, ψV*, xV, and aF. Elements of the algebraic dual space V* are sometimes called covectors or one-forms.

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