Computation of a Cubic B-Spline Basis and Its Derivatives

Computation of a cubic B-spline basis for arbitrary knots. It also provides the 1st and 2nd derivatives, as well as the integral of the basis elements. It is used by the author to fit penalized B-spline models, see e.g. Jullion, A. and Lambert, P. (2006) , Lambert, P. and Eilers, P.H.C. (2009) and, more recently, Lambert, P. (2021) . It is inspired by the algorithm developed by de Boor, C. (1977) .