In mathematics, the Christoffel–Darboux theorem is an identity for a sequence of orthogonal polynomials, introduced by Elwin Bruno Christoffel (1858) and Jean Gaston Darboux (1878). It states that
where fj(x) is the jth term of a set of orthogonal polynomials of squared norm hj and leading coefficient kj.
References
Christoffel–Darboux formula Wikipedia(Text) CC BY-SA