R/interruption.R

In loelschlaeger/vntrs: Variable Neighborhood Trust Region Search

#' Interrupt local search
#'
#' @description
#' This function checks if the local search can be interrupted prematurely.
#'
#' @inheritParams vntrs
#' @param point
#' The current location of the local search.
#' @inheritParams unique_optimum
#'
#' @return
#' \code{TRUE} for premature interruption, \code{FALSE} if not.
#'
#' @keywords
#' internal

interruption <- function(f, point, L, minimize) {
  ### no interruption if 'L' is empty
  if (length(L) == 0) {
    return(FALSE)
  }

  ### the value at the best iterate in L
  f_best <- do.call(
    what = ifelse(minimize, min, max),
    args = list(unlist(lapply(L, function(x) x$value)))
  )

  for (i in seq_len(length(L))) {
    ### compute distance between 'point' and identified optima
    dist <- norm(matrix(point - L[[i]]$argument), "F")

    ### check if distance is below 1
    if (dist <= 1) {
      cat(" [optimum already visted]")
      return(TRUE)
    }
  }

  ### check for convergence to a local optimum
  if (1e-3 >= norm(matrix(f(point)$gradient), "F") &&
    3 >= f(point)$value - f_best) {
    cat(" [optimum seems local]")
    return(TRUE)
  }

  ### otherwise do not interrupt
  return(FALSE)
}