R/Points.TLineSeg.R

In TML: Tropical Geometry Tools for Machine Learning

#'Sample k equally spaced points on a max- or min-plus tropical line segment
#'
#'This function calculates k equally spaced points on a tropical line segment
#'
#'@param D1 point in the tropical projective torus
#'@param D2 point in the tropical projective torus
#'@param k number of points
#'@param tadd function; max indicates max-plus addition, min indicates min-plus
#'  addition. Defaults to max
#'@return matrix of k equally spaced points on a tropical line segment
#'@author Ruriko Yoshida \email{ryoshida@@nps.edu}
#'@export
#' @examples
#'D1 <-c(0,4,2)
#'D2 <- c(0,7,-1)
#'Points.TLineSeg(D1, D2, k = 5)
#'Points.TLineSeg(D1, D2, k = 5,tadd=min)

Points.TLineSeg <- function(D1, D2, k = 20, tadd=max){
  d <- length(D1)
  k<-k+1
  x <- matrix(rep(0, d*(k)), k, d)
  decreasing <- identical(tadd, base::min)

  if(length(D1) != length(D2))
    warning("dimension is wrong!")


  index <- order(D2 - D1,decreasing = decreasing)
  lambda <- (D2 - D1)[index]
  L <- lambda[d] - lambda[1]

  for(j in 1:(k)) {
    for(i in 1:d){
      x[j, i] <- tadd((lambda[1] + (j * L)/k) + D1[i], D2[i])
    }
  }

  return(x[1:(nrow(x)-1),])
}