dual homomorphism
Definition.
Let be vector spaces over a field , and be a homomorphism (a linear map) between them. Letting denote the corresponding dual spaces, we define the dual homomorphism , to be the linear mapping with action
We can also characterize as the adjoint of relative to the natural evaluation bracket between linear forms and vectors:
To be more precise is characterized by the condition
If and are finite dimensional, we can also characterize the dualizing operation as the composition of the following canonical isomorphisms:
Category theory perspective.
The dualizing operation behaves contravariantly with respect to composition, i.e.
for all vector space homomorphisms with suitably matched domains. Furthermore, the dual of the identity homomorphism is the identity homomorphism of the dual space. Thus, using the language of category theory, the dualizing operation can be characterized as the homomorphism action of the contravariant, dual-space functor.
Relation to the matrix transpose.
The above properties closely mirror the algebraic properties of the matrix transpose operation. Indeed, is sometimes referred to as the transpose of , because at the level of matrices the dual homomorphism is calculated by taking the transpose.
To be more precise, suppose that and are finite-dimensional, and let be the matrix of relative to some fixed bases of and . Then, the dual homomorphism is represented as the transposed matrix relative to the corresponding dual bases of .
Title | dual homomorphism |
Canonical name | DualHomomorphism |
Date of creation | 2013-03-22 12:29:33 |
Last modified on | 2013-03-22 12:29:33 |
Owner | rmilson (146) |
Last modified by | rmilson (146) |
Numerical id | 10 |
Author | rmilson (146) |
Entry type | Definition |
Classification | msc 15A72 |
Classification | msc 15A04 |
Synonym | adjoint homomorphism |
Synonym | adjoint |
Related topic | LinearTransformation |
Related topic | DualSpace |
Related topic | DoubleDualEmbedding |