solver.lkh.R

#' @export
makeTSPSolver.lkh = function() {
  makeTSPSolverInternal(
    cl = "lkh",
    short.name = "LKH",
    name = "Lin-Kernigham Heuristic",
    properties = c("euclidean", "external", "requires.tsplib")
  )
}

# INTERNAL
# Helper to write config file needed by Helsgauns LKH implementation.
# PARAMETER = VALUE
#
# @param file.params [character(1)]
#   Path to file.
# @param args [list]
#   Named list of values.
# @return [Nothing]
writeToLKHParameterFile = function(file.params, args) {
  args = sapply(names(args), function(name) {
    if (is.integer(args[[name]])) {
      sprintf("%s = %i", name, args[[name]])
    } else if (is.numeric(args[[name]])) {
      sprintf("%s = %f", name, args[[name]])
    } else {
      sprintf("%s = %s", name, args[[name]])
    }
  })
  output = collapse(args, "\n")
  write(output, file = file.params)
}

#' @title Solver: LKH
#'
#' @description Inexact TSP solvers based the Lin-Kernigham heuristic.
#'
#' @note This solver requires integer inter-city distances.
#'
#' @references
#' Helsgaun, K. (2000). An effective implementation of the lin-kernighan traveling
#' salesman heuristic. European Journal of Operational Research, 126:106-130.
#'
#' Helsgaun, K. (2009). General k-opt submoves for the Lin-Kernighan TSP heuristic.
#' Mathematical Programming Computation, 1(2-3):119-163.
#'
#' @template arg_solver
#' @template arg_instance
#' @template arg_seed
#' @param cutoff.time [\code{integer(1)}]\cr
#'   Maximal running time in seconds.
#'   Default is NULL, i.e., no cutoff time.
#' @template arg_opt_tour_length
#' @param max.trials [\code{integer(1)}]\cr
#'   Maximal number of iterations.
#'   Default is the number of nodes of the instance.
#' @param with.restarts [\code{logical(1)}]\cr
#'   Should LKH restart if a plateau is reached?
#'   Default is \code{FALSE}.
#' @template arg_full_matrix
#' @template arg_verbose
#' @template arg_log_trajectory
#' @template arg_work_dir
#' @template arg_output_files_prefix
#' @template arg_keep_output_files
#' @param more.args [\code{list}]\cr
#'   Named list of parameter which shall be written to the LKH parameter file.
#'   Note that 1) the names should be all uppercase and 2) there is no argument
#'   check. Default ist the empty list.
#' @param ... [any]\cr
#'   Not used at the moment.
#' @template ret_TSPSolverResult
#' @export
run.lkh = function(solver, instance,
  seed = as.integer(ceiling(runif(1L) * 2^15)),
  cutoff.time = NULL,
  opt.tour.length = NULL,
  max.trials = NULL,
  with.restarts = FALSE,
  full.matrix = FALSE,
  verbose = FALSE,
  log.trajectory = TRUE,
  work.dir = NULL,
  output.files.prefix = NULL,
  keep.output.files = FALSE,
  more.args = list(),
  ...) {

  seed = asInt(seed, lower = 1L)
  if (!is.null(cutoff.time))
    cutoff.time = asInt(cutoff.time, lower = 0L)

  if (!is.null(opt.tour.length))
    opt.tour.length = asInt(opt.tour.length, lower = 1L)

  if (!is.null(max.trials))
    max.trials = asInt(max.trials, lower = 10L)

  assertFlag(with.restarts)
  assertFlag(full.matrix)
  assertFlag(verbose)
  assertFlag(log.trajectory)
  assertString(work.dir, null.ok = TRUE)
  assertString(output.files.prefix, null.ok = TRUE)
  assertFlag(keep.output.files)
  assertList(more.args)

  work.dir = BBmisc::coalesce(work.dir, tempdir())
  cur.dir = getwd()
  on.exit(setwd(cur.dir))
  setwd(work.dir)

  temp.file = BBmisc::coalesce(output.files.prefix, basename(tempfile(tmpdir = work.dir)))
  file.params = paste0(temp.file, ".par")
  file.output = paste0(temp.file, ".out")
  file.trajectory = paste0(temp.file, ".traj")

  has.temporary.input = FALSE
  if (testClass(instance, "Network")) {
    file.input = paste0(temp.file, ".tsp")
    has.temporary.input = TRUE
    if (full.matrix && any(round(instance$distance.matrix) != instance$distance.matrix)) {
      stopf("LKH can handle only integer distances!")
    }
    exportToTSPlibFormat(instance, filename = file.input, full.matrix = full.matrix, use.extended.format = FALSE, digits = 100)
  } else {
    file.input = instance
  }

  # the most important parameters are the PROBLEM_FILE, the number of RUNS,
  # the initial SEED for the generator of pseudo random numbers and TIME_LIMIT
  # in seconds.
  args = list()
  args$PROBLEM_FILE = file.input
  if (log.trajectory)
    args$OUTPUT_TRAJECTORY_FILE = file.trajectory
  args$RUNS = 1
  args$SEED = seed
  if (!is.null(cutoff.time))
    args$TIME_LIMIT = cutoff.time
  args$DO_RESTARTS = as.integer(with.restarts)

  if (!is.null(max.trials))
    args$MAX_TRIALS = max.trials

  if (!is.null(opt.tour.length)) {
    args$STOP_AT_OPTIMUM = "YES"
    args$OPTIMUM = opt.tour.length
  }

  # append additional arguments
  args = c(args, more.args)

  args$OUTPUT_TOUR_FILE = file.output
  writeToLKHParameterFile(file.params, args)

  # Write specific parameter file (deleted later)
  # $ in the output file name is replaced by tour length by LKH (see USER GUIDE)
  start.time = proc.time()
  solver.output = system2(solver$bin, args = file.params, stdout = verbose, stderr = verbose)
  runtime = as.numeric(proc.time() - start.time)
  if (verbose)
    print(solver.output)

  # build tour
  tmp = readTSPlibTOURFile(file.output)
  tour = tmp$tour
  tour.length = tmp$tour.length
  trajectory = NULL
  if (log.trajectory) {
    trajectory = read.table(file.trajectory, header = TRUE, sep = ",", stringsAsFactors = FALSE)
  }

  if (!keep.output.files)
    unlink(c(file.output, file.params, file.trajectory, file.trajectory))

  if (has.temporary.input)
    unlink(file.input)

  #distmat.file = paste0(work.dir, "/distmat.csv")

  solver.id = sprintf("LKH%s",
    if(with.restarts) "+restart" else "")
  if (!is.null(more.args$RECOMBINATION))
    solver.id = paste0(solver.id, "+", more.args$RECOMBINATION)

  list(
    solver.id = solver.id,
    tour = tour,
    tour.length = tour.length,
    error = NULL,#distmat.file,
    runtime = runtime,
    trajectory = trajectory,
    solver.output = solver.output
  )
}