NetLogo：询问有限数量的海龟，按变量值排序

Question

我正在尝试在 NetLogo（5.3.1，在 Mac Sierra 上）中对容量限制和优先级进行建模。它归结为要求有限数量的海龟（比如 n）做某些事情，并选择这些海龟，以便（1）它们满足特定条件并且（2）它们是 n 海龟变量的最大值 my-variable。

我正在尝试通过以下方式做到这一点：

let subset-of-turtles turtles with [ condition-variable = some-value ]
ask max-n-of n subset-of-turtles [ my-variable ] [< do something >]

但它有多个问题。

首先，如果没有乌龟满足[ condition-variable = some-value ]的条件，NetLogo会抛出一个错误

Requested n random agents from a set of only 0 agents.

我尝试通过在 ask 命令之前插入一行来解决：

let subset-of-turtles turtles with [ condition-variable = some-value ]
if subset-of-turtles != nobody [
  ask max-n-of n subset-of-turtles [ my-variable ] [< do something >]
  ]

但是不行:

observer> show turtles with [ condition-variable = some-value ]
observer: (agentset, 0 turtles)
observer> let subset-of-turtles turtles with [ condition-variable = some-value ] show subset-of-turtles != nobody
observer: true

NetLogo认为一个空的agentset仍然是一个agentset，所以它会通过不同于nobody的测试。

其次，即使有一些海龟满足条件，如果少于n，NetLogo 也会抛出同样的错误。我的模型是一个增长模型，在这个模型中，能力意味着一开始就足够了，然后就会达到约束。因此，这将发生在模型的每个运行中。

我希望 NetLogo 最多执行 ask 块中的命令 n 次。假设有m只海龟满足条件： 1.如果m <= n，对所有m只海龟执行命令 2. If m > n，执行my-variable值最高的n只海龟的命令。有人可以建议吗？

Answer 1

假设此设置：

turtles-own [
  condition-variable
  my-variable
]



to setup
  ca
  reset-ticks
  crt 10 [
    setxy random 30 - 15 random 30 - 15 
    set condition-variable random 2
    set my-variable 1 + random 10
  ]

end

~~首先，您可以使用 count 快速检查代理集是否为空，并将其用作您的条件。~~

不要这样做；正如@JenB 在接受的答案中所建议的那样，改用 any? 原语。

其次，你可以用ifelse来表达"If there are fewer turtles in the subset than n, only ask the turtles in the subset. Else, ask n turtles in the subset."

to go

  let n 5
  let subset-of-turtles turtles with [ condition-variable = 1 ]

  ;;  obtain the number of turtles in the subset
  let subcount count subset-of-turtles

  ;; If there are more than 0 turtles in the subset, do the following
  if subcount > 0 [
    ;; If n is greater than the number in the subset, only ask the subset
    ifelse n >= subcount [
      ask max-n-of subcount subset-of-turtles [ my-variable ] [
        set size 2
      ]
    ]
    ;; If n is NOT greater than the number in the subset, ask n of the subset
    [
      ask max-n-of n subset-of-turtles [ my-variable ][
        set size 2
      ]
    ]
  ]  
end

Answer 2

一般来说，我不建议测试是否count <agentset> = 0，因为NetLogo仍然需要构造agentset来统计它。但是，有一个非常方便的 any? 记者可以完成这项任务。因此，尝试对原始代码进行以下修改：

let subset-of-turtles turtles with [ condition-variable = some-value ]
if any? subset-of-turtles [
  ask max-n-of n subset-of-turtles [ my-variable ] [< do something >]
  ]

NetLogo：询问有限数量的海龟，按变量值排序

NetLogo: Asking a limited number of turtles, ranked by the value of a variable

constraints

ranking

netlogo