Source: /cirosantilli/adjoint-operator

= Adjoint operator
{title2=$A^\dagger$}

Given a <linear operator> $A$ over a space $S$ that has a <inner product> defined, we define the adjoint operator $A^\dagger$ (the $\dagger$ symbol is called "dagger") as the unique operator that satisfies:
$$
\forall v, w \in S, <Av, w> = <v, A^{\dagger} w>
$$