在看例子时有几个问题看不懂

yanyanxihua · 发表于 2012-6-20 08:59:43

新手，在看netlogo自带的例子时，有几行程序看不懂，希望高手能够指点。
netlogo自带的social science--traffic grid这一例子当中，
globals
[
  grid-x-inc             ;; the amount of patches in between two roads in the x direction
  grid-y-inc             ;; the amount of patches in between two roads in the y direction
  acceleration          ;; the constant that controls how much a car speeds up or slows down by if
                        ;; it is to accelerate or decelerate
  phase                   ;; keeps track of the phase
  num-cars-stopped       ;; the number of cars that are stopped during a single pass thru the go procedure
  current-light          ;; the currently selected light

  ;; patch agentsets
  intersections ;; agentset containing the patches that are intersections
  roads       ;; agentset containing the patches that are roads
]

turtles-own
[
  speed    ;; the speed of the turtle
  up-car? ;; true if the turtle moves downwards and false if it moves to the right
  wait-time ;; the amount of time since the last time a turtle has moved
]

patches-own
[
  intersection? ;; true if the patch is at the intersection of two roads
  green-light-up? ;; true if the green light is above the intersection.  otherwise, false.
               ;; false for a non-intersection patches.
  my-row       ;; the row of the intersection counting from the upper left corner of the
               ;; world.  -1 for non-intersection patches.
  my-column    ;; the column of the intersection counting from the upper left corner of the
               ;; world.  -1 for non-intersection patches.
  my-phase       ;; the phase for the intersection.  -1 for non-intersection patches.
  auto?          ;; whether or not this intersection will switch automatically.
               ;; false for non-intersection patches.
]

;;;;;;;;;;;;;;;;;;;;;;
;; Setup Procedures ;;
;;;;;;;;;;;;;;;;;;;;;;

;; Initialize the display by giving the global and patch variables initial values.
;; Create num-cars of turtles if there are enough road patches for one turtle to
;; be created per road patch. Set up the plots.
to setup
  ca
  setup-globals

  ;; First we ask the patches to draw themselves and set up a few variables
  setup-patches
  make-current one-of intersections
  label-current

  set-default-shape turtles "car"

  if (num-cars > count roads)
  [
user-message (word "There are too many cars for the amount of "
                     "road.  Either increase the amount of roads "
                     "by increasing the GRID-SIZE-X or "
                     "GRID-SIZE-Y sliders, or decrease the "
                     "number of cars by lowering the NUMBER slider.\n"
                     "The setup has stopped.")
stop
  ]

  ;; Now create the turtles and have each created turtle call the functions setup-cars and set-car-color
  crt num-cars
  [
setup-cars
set-car-color
record-data
  ]

  ;; give the turtles an initial speed
  ask turtles [ set-car-speed ]

  reset-ticks
end

;; Initialize the global variables to appropriate values
to setup-globals
  set current-light nobody ;; just for now, since there are no lights yet
  set phase 0
  set num-cars-stopped 0
  set grid-x-inc world-width / grid-size-x
  set grid-y-inc world-height / grid-size-y

  ;; don't make acceleration 0.1 since we could get a rounding error and end up on a patch boundary
  set acceleration 0.099
end

;; Make the patches have appropriate colors, set up the roads and intersections agentsets,
;; and initialize the traffic lights to one setting
to setup-patches
  ;; initialize the patch-owned variables and color the patches to a base-color
  ask patches
  [
set intersection? false
set auto? false
set green-light-up? true
set my-row -1
set my-column -1
set my-phase -1
set pcolor brown + 3
  ]

  ;; initialize the global variables that hold patch agentsets
  set roads patches with
[(floor((pxcor + max-pxcor - floor(grid-x-inc - 1)) mod grid-x-inc) = 0) or
(floor((pycor + max-pycor) mod grid-y-inc) = 0)]
  set intersections roads with
[(floor((pxcor + max-pxcor - floor(grid-x-inc - 1)) mod grid-x-inc) = 0) and
(floor((pycor + max-pycor) mod grid-y-inc) = 0)]

  ask roads [ set pcolor white ]
setup-intersections
end
其中定义道路的句子，如下所示，是什么意思啊？
set roads patches with
[(floor((pxcor + max-pxcor - floor(grid-x-inc - 1)) mod grid-x-inc) = 0) or
(floor((pycor + max-pycor) mod grid-y-inc) = 0)]
谁能帮我解释一下[(floor((pxcor + max-pxcor - floor(grid-x-inc - 1)) mod grid-x-inc) = 0)是什么意思吗？

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