The first item is the primary reference for this program.
Smith, Robert E., Jr.; Price, Joseph M.; and Howser, Lona M.:
A Smoothing Algorithm Using Cubic Spline Functions.
NASA Technical Note D-7397, February 1974.
De Boor, Carl; and Rice, John R.:
Least Squares Cubic Spline Approximation I - Fixed Knots. CSD TR 20, Purdue Univ., Apr. 1968.
De Boor, Carl; and Rice, John R.: Least Squares Cubic Spline Approximation 11 - Variable
Knots. CSD TR 21, Purdue Univ., Apr. 1968.
Smith, Patricia J.:
FITLOS: A FORTRAN Program for Fitting Low-Order Polynomial
Splines by the Method of Least Squares.
NASA Technical Note D-6401, August 1971.
Ahlberg, J. H.; Nilson, E. N.; and Walsh, J. L.: The Theory of Splines and Their Applications.
Academic Press, Inc., 1967.
Bliss, Gilbert A.: Lectures on the Calculus of Variations. Univ. of Chicago Press,
c. 1946.
Guest, P. G.: Numerical Methods of Curve Fitting. Cambridge Univ. Press, 1961.
Hadley, G.: Nonlinear and Dynamic Programming. Addison-Wesley Pub. Co., Inc.,
C. 1964, pp. 212-213.
Lee, E.T.Y.: Choosing nodes in parametric curve interpolation.
Computer-Aided Design, vol. 21, no. 6, Jul-Aug 1989, pp.363-370.
[Access PDF from Wikipedia under smoothing spline.]
Graham, N.Y.: Smoothing with Periodic Cubic Splines.
Bell System Technical Journal, vol. 62 no. 1, Jan 1983, pp 101-110.
[Access PDF from Wikipedia under smoothing spline.]
Morgan,Jr.,Harry L.:
Computer Program for Plotting and Fairing Wind-Tunnel Data.
NASA Technical Memorandum TM-85648, July, 1983.