Let V {\displaystyle {}V} be a finite-dimensional K {\displaystyle {}{\mathbb {K} }} -vector space, endowed with an inner product, and let v 1 , v 2 , … , v n {\displaystyle {}v_{1},v_{2},\ldots ,v_{n}} be a basis of V {\displaystyle {}V} .
orthonormal basis u 1 , u 2 , … , u n {\displaystyle {}u_{1},u_{2},\ldots ,u_{n}} of V {\displaystyle {}V} with
for alle