In mathematics, the complex conjugate of a complexvector space is a complex vector space , which has the same elements and additive group structure as , but whose scalar multiplication involves conjugation of the scalars. In other words, the scalar multiplication of satisfies
where is the scalar multiplication of and is the scalar multiplication of .
The letter stands for a vector in , is a complex number, and denotes the complex conjugate of .
More concretely, the complex conjugate vector space is the same underlying real vector space (same set of points, same vector addition and real scalar multiplication) with the conjugate linear complex structureJ (different multiplication by i).
A linear map gives rise to a corresponding linear map which has the same action as . Note that preserves scalar multiplication because
Thus, complex conjugation and define a functor from the category of complex vector spaces to itself.
If and are finite-dimensional and the map is described by the complex matrix with respect to the bases of and of , then the map is described by the complex conjugate of with respect to the bases of and of .
Given a Hilbert space (either finite or infinite dimensional), its complex conjugate is the same vector space as its continuous dual space.
There is one-to-one antilinear correspondence between continuous linear functionals and vectors.
In other words, any continuous linear functional on is an inner multiplication to some fixed vector, and vice versa.
Thus, the complex conjugate to a vector , particularly in finite dimension case, may be denoted as (v-star, a row vector which is the conjugate transpose to a column vector ).
In quantum mechanics, the conjugate to a ket vector is denoted as – a bra vector (see bra–ket notation).