elevator simulation code

elevator.R

nmin <- 120;
time <- nmin * 60;
lambda <- 10/60; # 10 passengers every minute, on average
arrivals <- rpois(time, lambda);
population <- sum(arrivals);

nelev <- 4; # number of elevators
nfloor <- 7; # number of floors
elevators <- matrix(1, ncol=nelev, nrow=time)

entry <- 10; # seconds for doors to open, people to enter, doors to close
exit <- 10; # seconds for doors to open, people to leave, doors to close
speed <- 1/5; # floors/second

max <- 10; # (soft) maximum number of passengers per car

waiting <- 0; # how many people are currently waiting
waittimes <- integer(0); # vector of waiting times for currently waiting
totalwait <- integer(0); # total wait for those whose elevators left before the end

passengers <- integer(nelev); # number of passengers boarding each elevator
departing <- integer(nelev); # number of seconds until each elevator will depart, if boarding

for (t in 1:time) {
  # any elevators about ready to go?
  if (any(departing == 1)) {
    leaving <- which(departing == 1);
    while (length(leaving)) {
      elevator <- leaving[1];
      leaving <- leaving[-1];

      totalwait <- c(totalwait, waittimes[1:passengers[elevator]]);
      waittimes <- waittimes[-(1:passengers[elevator])];
      dests <- sample(2:nfloor, passengers[elevator], replace=T); # random individual destinations
      stops <- sort(unique(dests)); # floors to stop at
      dists <- rev(rev(stops) - c(rev(stops)[-1],1)); # distance between stops

      offset <- t;
      d <- 1;
      while (offset < time && d <= length(dists)) {
        # time spent between stops:
	enroute <- min(offset+as.integer(round(dists[d] / speed, 0)), time);
        elevators[offset:enroute, elevator] <- NA;
	offset <- enroute;

	# time spent exiting at each stop:
	onfloor <- min(offset+exit, time);
        elevators[offset:onfloor, elevator] <- stops[d];
        offset <- onfloor+1;

	d <- d + 1;
      }

      # time spent returning back to first floor:
      if (offset < time) {
        enroute <- min(offset+as.integer(round(sum(dists)/speed, 0)), time);
        elevators[offset:enroute, elevator] <- NA;
      }

      passengers[elevator] <- 0; # reset passenger count.
    }
  }

  # count down for departing elevator(s):
  departing <- departing - ifelse(departing, 1, 0);

  # add any new arrivals to the waiting line:
  waiting <- waiting + arrivals[t];
  waittimes <- c(waittimes, rep(0, arrivals[t]));

  if (waiting > 0) {
    # board anyone we can:
    available <- which(elevators[t,] == 1 & passengers <= max);
    while (waiting > 0 && length(available) > 0) {
      elevator <- available[1]; # first available elevator
      available <- available[-1]; # remove this elevator from available list

      boarding <- min(waiting, max-passengers[elevator]); 
      passengers[elevator] <- passengers[elevator] + boarding;
      waiting <- waiting - boarding;

      # mark when this elevator will depart: "entry" seconds for first passenger(s),
      # and +1 additional second for each new set of arrivals before departure
      departing[elevator] <- departing[elevator] + ifelse(departing[elevator], 1, entry)
    }
  }

  # update how long everyone has been waiting:
  waittimes <- waittimes + 1;

}

image(list(x=1:500, y=1:4, z=elevators[1:500,]),col=rainbow(7), ylab="elevator",xlab="time")
for (f in 1:nelev) {
  floors <- rle(elevators[1:500, f]);
  text(cumsum(floors$lengths)[!is.na(floors$values)]-(exit/2), f, floors$values[!is.na(floors$values)])
}

Hi,

this is probably late to ask, but why do you add an additional second for each new set of arrivals before departure on line 84?

Thanks

Something else: variable population is never used :)