R/cpm.R

In antoanne/ifmFramework: Financial evaluation of Projects

#' The critical path method (CPM) is a step-by-step project management technique for process
#' planning that defines critical and non-critical tasks with the goal of preventing time-frame
#' problems and process bottlenecks#' activities are "critical," meaning that they have to be done on time or else
#' the whole project will take longer.
#'
#' @name cpm
#'
#' @aliases critical.path.method critical_path_method
#'
#' @param activities.duration Vector with activities duration.
#' @param activities.successors Vector with dependencies between activities.
#'
#' @description The Critical Path Method or Critical Path Analysis, is a
#' mathematically based algorithm for scheduling a set of project activities.
#'
#' CPM will get how long your complex project will take to complete and which
#' activities are "critical," meaning that they have to be done on time or else
#' the whole project will take longer.
#'
#' @export
#'
#' @return Returns list of EST (Early Start Time), EFT(Early Finish Time),
#' LST(Lately Start Time), LFT (Lately Finish Time) using Forward Pass and Backward Pass
#'
#' @keywords critical path, scheduling, project activities
#'
#' @family scheduling
#'
#' @examples
#' ex.cpm.activities.duration <- c(1,4,5,7,2,3,1)
#' ex.cpm.activities.successors <- list(c(2,3), 4, c(4,5), 6, 7, 7, c(0))
#' ex.cpm <- cpm(ex.cpm.activities.duration,
#'               ex.cpm.activities.successors)
#'
cpm <- critical.path.method <- critical_path_method <-
  function(activities.duration = c(1,4,5,7,2,3,1),
           activities.successors = list(c(2,3), 4, c(4,5), 6, 7, 7, c(0)))
    {

      activities.predecessors <- utils.suc2pred(activities.successors)

      activities.quantity <- length(activities.duration)
      #generates early and late start times of for a cpm network
      est<-vector (mode="numeric", length=activities.quantity)
      eft<-vector (mode="numeric", length=activities.quantity)
      lst<-vector (mode="numeric", length=activities.quantity)
      lft<-vector (mode="numeric", length=activities.quantity)

      #Functions
      cpm.forward <- function(s=1){
        #find early start and finish times
        eft[s] <<- est[s] + activities.duration[s]
        if (activities.successors[[s]][1]!=0){
          for (i in activities.successors[[s]]){
            if (est[i] < eft[s]){
              est[i]<<-eft[s]
            }
            cpm.forward(i)
          }
        }
      }

      cpm.backward<-function(s){
        #find late start and finish times
        lst[s]<<-lft[s] - activities.duration[s]
        if (activities.predecessors[[s]][1]!=0){
          for (i in activities.predecessors[[s]]){
            if (lft[i]>lst[s]){
              lft[i]<<-lst[s]
            }
            cpm.backward(i)
          }
        }
      }

      #Main
      cpm.forward()
      lft<-rep(eft[activities.quantity], times=activities.quantity)
      cpm.backward(activities.quantity)
      return(list('est' = est, 'eft' = eft,
                  'lst' = lst, 'lft' = lft))
    }