R/Bspline.R

In ManonMartin/SOAP-NMR: Pre-process 1H-NMR FID signals

# B-spline basis for the warping function
Bspline <- function(x, x0, x1, ndx, deg = 3) {
  if (min(x) < x0 | max(x) > x1) {
    stop("Some elements of x out of bounds !!")
  }
  dx <- (x1 - x0)/ndx
  t <- x0 + dx * ((-deg):(ndx - 1))
  Tt <- matrix(1, nrow = length(x), ncol = 1) %*% t
  X <- x %*% matrix(1, nrow = 1, ncol = length(t))
  D <- (X - Tt)/dx
  B <- t(diff(rbind(rep.int(0, length(x)), t(D <= 1))))
  r <- c(2:length(t), 1)
  for (k in 1:deg) {
    B <- (D * B + (k + 1 - D) * B[, r])/k
  }  #FIXME sparse ?
  return(B)
}