尝试移动到最近的品种时，是什么导致了 "Nobody" 错误？

Question

我做了一个老虎吃狼的模型。当老虎的能量大于狼能量总和的一半时，老虎就会找到离它最近的狼，吃掉它并获得能量。所以我写道：

to tigers-feed
  ask tigers [
    let WE-sum sum [WEnergy] of wolves
    if TEnergy > WE-sum * 0.5 [
      move-to min-one-of wolves [distance myself] ;;it reports bugs here.
      ask one-of wolves-here [die]
      set TEnergy Wt * tiger-gain-from-food
    ]
  ]

但是当运行执行to go命令时，程序会警告我：

MOVE-TO expected input to be an agent but got NOBODY instead.

这是我的完整代码：

globals[
  Ww
  Wt
  wolf-gain-from-food
  tiger-gain-from-food
]

breed [wolves wolf]
breed [tigers tiger]

wolves-own [WEnergy]
tigers-own [TEnergy]

;;probably nothing wrong with here, you can jump them.
to setup
  clear-all
  parameter-initialization
  setup-breed
  reset-ticks
end

to parameter-initialization
  set Ww random 2
  set Wt random 4
  set wolf-gain-from-food 100
  set tiger-gain-from-food 200
end

to setup-breed

  set-default-shape wolves "wolf"
  create-wolves 100 [setxy random-xcor random-ycor]
  ask wolves [
    set WEnergy Ww * wolf-gain-from-food
    set size 4
    set color grey
  ]

  set-default-shape tigers "x"
  create-tigers 1 [setxy random-xcor random-ycor]
  ask tigers [
    set TEnergy Wt * tiger-gain-from-food
    set size 6
    set color yellow
  ]

end



to go
  ask tigers [set TEnergy TEnergy + 2]
  tigers-feed
  tick
end

to tigers-feed
  ask tigers [
    let WE-sum sum [WEnergy] of wolves
    
    if TEnergy > WE-sum * 0.5 [
      move-to min-one-of wolves [distance myself]
      ask one-of wolves-here [die]
      set TEnergy Wt * tiger-gain-from-food
    ]
  ]

end

事实上，当我尝试运行只执行一次时，程序并没有报错。所以我想这不是导致错误的命令 move-to min-one-of wolves [distance myself] 。那么究竟是什么导致了错误呢？

Answer 1

给你错误的那一行实际上是 move-to min-one-of wolves [distance myself].

如您所见，只有当模型中没有狐狸时才会出现错误。这是因为您没有包含停止条件或任何其他阻止模型在 none.

处搜索狼的条件

假设当老虎吃掉所有的狼时你很高兴让模型停止，你可以这样做：

to go
  if (not any? wolves) [stop]
  ask tigers [set TEnergy TEnergy + 2]
  tigers-feed
  tick
end

请注意，写 any? <agentset> 等同于写 count <agentset> > 0 但是，正如 NetLogo 词典中正确建议的那样，it is more efficient and readable for this purpose（在我们的例子中，我们必须添加 not在它之前）。

尝试移动到最近的品种时，是什么导致了 "Nobody" 错误？

When trying to move to nearest breed, what causes the "Nobody" error?

agent-based-modeling

netlogo