R/bsplineS.R

In fda: Functional Data Analysis

bsplineS <- function (x, breaks, norder=4, nderiv=0, returnMatrix=FALSE)
{
#  This is a wrapper function for the S-PLUS spline.des function.
#  The number of spline functions is equal to the number of
#     discrete break points, length(BREAKVALUES), plus the order, NORDER,
#           minus 2.
#  Arguments are as follows:
#  X      ... array of values at which the spline functions are to
#             evaluated
#  BREAKS ... a STRICTLY INCREASING sequence of break points or knot
#             values.  It must contain all the values of X within its
#             range.
#  NORDER ... order of spline (1 more than degree), so that 1 gives a
#             step function, 2 gives triangle functions,
#             and 4 gives cubic splines
#  NDERIV ... highest order derivative.  0 means only function values
#             are returned.
#  Return is a matrix with length(X) rows and number of columns equal to
#                   number of b-splines

#  last modified 6 May 2012 by Spencer Graves
#  previously modified 2 April 2012 by Jim Ramsay

  x <- as.vector(x)
  n <- length(x)
  tol <- 1e-14
  nbreaks <- length(breaks)
  if (nbreaks < 2) stop('Number of knots less than 2.')
  if (min(diff(breaks)) < 0 ) stop('Knots are not increasing')

  if ( max(x) > max(breaks) + tol ||
       min(x) < min(breaks) - tol )
     stop('Knots do not span the values of X')
  if ( x[n] > breaks[nbreaks]) breaks[nbreaks] <- x[n]
  if ( x[1] < breaks[1]      ) breaks[1]       <- x[1]

  if (norder > 20) stop('NORDER exceeds 20.')
  if (norder <  1) stop('NORDER less than 1.')
  if (nderiv > 19) stop('NDERIV exceeds 19.')
  if (nderiv <  0) stop('NDERIV is negative.')
  if (nderiv >= norder) stop (
         'NDERIV cannot be as large as order of B-spline.')

  knots  <- c(rep(breaks[1      ],norder-1), breaks,
              rep(breaks[nbreaks],norder-1)  )
  derivs <- rep(nderiv,n)
  nbasis <- nbreaks + norder - 2
  if (nbasis >= norder) {
      if (nbasis > 1) {
  	    basismat <- Matrix(spline.des(knots, x, norder, derivs)$design)
      } else {
  	    basismat <- as.matrix(spline.des(knots, x, norder, derivs)$design)
      }
      if((!returnMatrix) && (length(dim(basismat)) == 2)){
          return(as.matrix(basismat))
      }
      return(basismat)
  } else {
      stop("NBASIS is less than NORDER.")
  }
}