Inner product determined by a basis ($⟨u,v{⟩}_e={\sum }_i{u}_i\overline{v_i}$)

Each basis $e_1,\dots ,e_n$ of a finite-dimensional complex vector space determines a unique complex inner product making that basis orthonormal. In coordinates it is $⟨{\sum }_i{u}_i{e}_i,{\sum }_i{v}_i{e}_i{⟩}_e={\sum }_i{u}_i\overline{v_i}$, with the first argument linear. The formula is sesquilinear, has conjugate symmetry, and satisfies $⟨v,v{⟩}_e={\sum }_i|v_i{|}^2$, which is positive unless $v=0$. Expanding any inner product in the given basis proves uniqueness. Its codomain is the complex numbers; only its diagonal values are necessarily real. The resulting identification with the dual space is conjugate-linear, not complex-linear.