Generates the I-spline basis matrix associated with integrated spline basis functions. Created by Cai and Wang in October, 2009.
Ispline(x, order, knots)the predictor variables.
the order of the basis functions.
a sequence of increasing points specifying the placement of the knots.
An I-spline basis matrix of dimension c(length(knots)+order-2, length(x)).
Wang, L., McMahan, C., and Hudgens, M. (2014+). A flexible and computationally efficient method for fitting the proportional hazards model to interval censored data. Submitted.
Ramsay, J. (1988). Monotone regression splines in action. Statistical Science 3, 425-441.