《基于Agent与个体的建模》第5章蝴蝶Hilltopping习题corridor width结果不符问题

安全阿岳

2026-10-4

问题根源

核心错误是corridor-width计算逻辑不符合习题定义：书中走廊宽度为「被踩踏过的patch总数」除以「所有蝴蝶从起点到山顶的平均移动总路程」，你当前用的是蝴蝶到起点的直线距离作为分母，数值远小于实际路程，导致结果大幅偏低。
缺少蝴蝶到达山顶后的停止逻辑：如果蝴蝶到达山顶后继续移动，会导致总路程统计虚高，进一步压低计算结果。
隐式上下文赋值有歧义：在turtle上下文直接修改patches-own的used?变量，部分NetLogo版本可能出现赋值异常。

修复方案

给turtles新增total-distance变量，记录每只蝴蝶移动的总步数
修改corridor-width的分母为所有蝴蝶的total-distance平均值
新增山顶判定逻辑，蝴蝶到达山顶后停止移动
明确used?变量的赋值对象为当前所在patch

修复后完整代码

patches-own [elevation used?]
turtles-own [start-patch total-distance reached-peak?]

to setup
  ca
  ask patches
  [
    set elevation 200 + (100 * (sin (pxcor * 3.8) + sin (pycor * 3.8)))
    set pcolor scale-color green elevation 0 400
    set used? false
  ]

  reset-ticks

  create-turtles 500
  [
    set size 2
    setxy 71 69
    pen-down
    set start-patch patch-here
    set total-distance 0
    set reached-peak? false
  ]
end

to go
  ask turtles with [not reached-peak?] [move]
  plot corridor-width
  tick
  if ticks >= 1000 or all? turtles [reached-peak?] [
    output-print word "Corridor width: " corridor-width 
    stop
  ]
end

to-report corridor-width
  let countpatches count patches with [used?]
  let mean-traveled mean [total-distance] of turtles
  report countpatches / mean-traveled
end

to move
  ; 判定是否到达山顶
  if elevation >= max [elevation] of neighbors [
    set reached-peak? true
    stop
  ]
  ifelse random-float 1.0 < q
    [uphill elevation 1]
    [move-to one-of neighbors]
  set total-distance total-distance + 1
  ask patch-here [set used? true]
end