R/bfa_subtree.R

In bifurcatingr: Bifurcating Autoregressive Models

#' Subtree Extractor
#'
#' This function extracts subtree of size \eqn{(2^p-1)} from the end of a given
#' bifurcating autoregressive tree (model) of order p.
#' @param n subtree size (integer)
#' @param p an integer determining the order of bifurcating autoregressive model
#' @return A numeric vector representing a subtree of size \eqn{(2^p-1)} from
#'   the end of a given bifurcating autoregressive tree.
#' @export
#' @examples
#' bfa_subtree(31, 1)
#' bfa_subtree(31, 2)
bfa_subtree <- function(n, p){
  Rs <- floor((n)/(2^(p-1)))
  subtree <- c()
  for(R in Rs){
    indx <- NULL
    for (i in 0:10){
      ind <- ((2^i)*R):((2^i)*R+(2^i-1))
      indx <- c(indx,if(utils::tail(ind, n=1)<=n){ind})
    }
    subtree <- append(subtree, c(indx))
  }
  subtree
}