NetLogo中使用tie的链接未正常工作问题排查

目标是创建2辆主车（cars），每辆主车后方配置6个跟随者（followers），让跟随者在主车后方均匀排成队列，通过tie链接依次绑定，实现主车移动时拉动整个队列。但当前代码仅主车与最近的第一个跟随者的tie生效，后续跟随者无法被拉动。

用户提供的代码如下：

globals [small  len_small ]
breed [cars car]
breed [followers follower]

cars-own [reg no_foll  len]
followers-own [reg]

to setup
  clear-all
   set small 2
   set len_small 7
 
  ask patches with [pycor >= 5 or pycor <=  1][set pcolor red]
  ask patches with [pycor = 4 ][set pcolor blue]
   ask patches with [ pycor = 2][set pcolor blue + 1]
  ask patches with [pycor = 3][set pcolor white]
  make_small
  reset-ticks

end

to go
  ask cars [forward 2]
  
end

to make_small
 create-cars  small  [move-to one-of patches with [pcolor = white  ]
    set shape "circle" set color red  set reg who set no_foll 0  set len len_small
    set heading one-of  [90 270]]
  
   create-followers (len_small - 1) * small [ set shape "car" set color red move-to one-of cars with [color = red and no_foll < (len_small - 1)]
    set heading [heading] of one-of cars-here + 180 set reg [reg] of one-of cars-here ask one-of cars-here [set no_foll no_foll + 1]]
  form_small_car
end

to form_small_car
  ask followers with [color = red ] [while [any? other turtles-here with [reg = [reg] of myself]][forward 1]]
  ask cars with [color = red] [let foll_behind_list followers-on patch-ahead -1 let foll_behind one-of foll_behind_list with [reg = [reg] of myself] create-link-to foll_behind [tie]]
  ask followers with [color = red and any? followers-on patch-ahead -1] [let foll_behind_list followers-on patch-ahead -1 let foll_behind one-of foll_behind_list with [reg = [reg] of myself ] 
  create-link-to foll_behind [tie]]
 end

核心问题分析 #

• 跟随者队列排列逻辑失效：当前仅让重叠的跟随者向前挪1步，无法让同组（同reg）的跟随者形成从主车开始依次向后的有序队列。所有跟随者初始都堆在主车格子，挪步后位置依然混乱，导致后续无法准确找到队列中的下一个跟随者。
• 链接创建逻辑随机且无序：
  1. 主车和跟随者创建链接时用one-of随机选择，无法确保选中的是队列中紧跟主车的第一个跟随者；
  2. 跟随者之间创建链接时，同样随机选择patch-ahead -1格子里的跟随者，且因队列无序，该格子里可能没有同组的下一个跟随者，导致后续链接无法创建；
  3. 没有按队列顺序依次绑定，而是所有海龟同时执行链接创建，无法形成“主车→跟随者1→跟随者2→…→跟随者6”的链式绑定。

修正方案 #

要实现有序队列和链式tie绑定，需先对每个reg组的主车和跟随者排序，再按顺序绑定并排列：

修改form_small_car过程如下：

to form_small_car
  ; 遍历每辆主车，处理其对应的跟随者组
  ask cars [
    ; 筛选出当前主车的同组海龟（主车+所有对应跟随者）
    let my-group (turtles with [reg = [reg] of myself])
    ; 按到主车的距离排序，主车为第一个，跟随者由近到远排列
    let sorted-group sort-by [ [a b] -> distance myself < distance myself ] my-group
    ; 依次给相邻海龟创建tie链接，并排列成队列
    foreach range (length sorted-group - 1) [ i ->
      let front-turtle item i sorted-group
      let back-turtle item (i + 1) sorted-group
      ; 前面的海龟绑定后面的海龟，确保移动时能拉动
      ask front-turtle [ create-link-to back-turtle [ tie ] ]
      ; 让后面的海龟移动到前面海龟的正后方1格，形成整齐队列
      ask back-turtle [
        face front-turtle
        forward 1
      ]
    ]
  ]
end

另外可优化make_small中跟随者的初始位置，避免全部堆在主车格子：
将创建跟随者的代码中move-to one-of cars...改为：

move-to patch-ahead -1 of one-of cars with [color = red and no_foll < (len_small - 1)]

这样初始时跟随者会落在主车后方格子，减少后续排序和移动的工作量。

内容的提问来源于stack exchange，提问作者Kevin A