R/minimummeancycle.R

In rlemon: R Access to LEMON Graph Algorithms

##' Finds the Minimum Mean Cycle in directed graphs.
##'
##' For details on LEMON's implementation, including differences between the
##' algorithms, see \url{https://lemon.cs.elte.hu/pub/doc/1.3.1/a00614.html}.
##' @title Solver for Minimum Mean Cycle
##' @param arcSources Vector corresponding to the source nodes of a graph's
##'   edges
##' @param arcTargets Vector corresponding to the destination nodes of a graph's
##'   edges
##' @param arcDistances Vector corresponding to the distances of a graph's edges
##' @param numNodes The number of nodes in the graph
##' @param algorithm Choices of algorithm include "Howard", "Karp", and
##'   "HartmannOrlin". "Howard" is the default.
##' @return A named list containing two entries: 1) "cost": a vector containing
##'   the costs of each edge in the Minimum Mean Cyckle, and 2) "nodes": the
##'   nodes in the Minimum Mean Cycle.
##' @export
MinMeanCycle <- function(arcSources,
                         arcTargets,
                         arcDistances,
                         numNodes,
                         algorithm = "Howard") {

  check_graph_vertices(arcSources, arcTargets, numNodes)
  check_arc_map(arcSources, arcTargets, arcDistances, numNodes)
  check_algorithm(algorithm)

  algfn <- switch(algorithm,
                  "Howard" = HowardMmcRunner,
                  "Karp" = KarpMmcRunner,
                  "HartmannOrlin" = HartmannOrlinMmcRunner,
                  stop("Invalid algorithm.")
                  )
  result <- algfn(arcSources, arcTargets, arcDistances, numNodes)
  names(result) <- c("costs", "nodes")
  return(result)
}