The word adjoint has a number of related meanings. In linear algebra, it refers to the conjugate transpose and is most commonly
denoted . The analogous concept applied to
an operator instead of a matrix, sometimes also known
as the Hermitian conjugate (Griffiths 1987, p. 22), is most commonly denoted
using dagger notation (Arfken 1985). The adjoint operator is very common in both
Sturm-Liouville theory and quantum mechanics.
For example, Dirac (1982, p. 26) denotes the adjoint of the bra
vector as , or .