Netlogo让海龟在一个区域内随意行走

假设我有一个海滩和一个海洋，分别用灰色和青色补丁表示。我有一些海龟（鱼），我将它们的起始位置随机限制在海洋的某个地方。现在，鱼的每一个刻度都按照从正态分布（均值 = 0，SD = 1）得出的步长进行随机游走。从逻辑上讲，当移动鱼时，应该留在海洋中而不是移动到海滩上。我尝试了与while []将鱼的起始位置限制在海洋相同的方法，但这似乎在这里不起作用，即鱼根本不动。有什么想法吗？

编辑：除了在水中有 2 条鱼外，我还有 2 只其他海龟（例如牛和羊）在陆地上，与鱼类似，它们在移动时不能/不应该进入水中（实际上我有 3这样的“栖息地”总和，乌龟不应该离开它们开始的栖息地）。当我将 LeirsW 的解决方案用于鱼和牛/羊时，我的 Netlogo 冻结了，我不得不强制退出。对此有什么想法吗？

编辑 2： x0 和 y0 没有错误，需要保留在代码中。

更新代码如下：

breed [ fishes fish ]

fishes-own
[
  x0 y0 xcur ycur
]

to setup

  clear-all
  reset-ticks

  ask patches [set pcolor gray]
  ask patches with [ pycor < (max-pycor / 2) ] [ set pcolor cyan ]

  create-fishes 4
    [
      setxy random-xcor random-ycor
      set x0 xcor
      set y0 ycor

      ifelse who <= ( 3 * 0.5 )       ; Set proportion of fishes in lagoon determined by slider
        [ set shape "fish" set size 2 ]
        [ set shape "fish" set size 3 ]

      set color white

      while [ pcolor != cyan ] [ setxy random-xcor random-ycor ]                   ; Set fishes coordinates for lagoon habitat only
    ]

  create-fishes 4
    [
      setxy random-xcor random-ycor
      set x0 xcor
      set y0 ycor

      ifelse who <= ( 4 - 1 + 4 * 0.5 )
        [ set shape "sheep" set size 2 set color yellow ]
        [ set shape "cow" set size 2  set color yellow]

      ;set color white

      while [ pcolor != gray ] [ setxy random-xcor random-ycor ]                   ; Set fishes coordinates for bank habitat only
    ]

end

to go

  fish-move

  tick

end

to fish-move

  ask fishes with [pcolor = cyan]
    [

          ifelse (random-float 1) < 0.95
            [
              let destination patch (x0 + random-normal 0 1) (y0 + random-normal 0 1)

              while [ [pcolor] of destination != cyan ]
                [
                  set destination patch (x0 + random-normal 0 1) (y0 + random-normal 0 1)
                ]
              move-to destination

              set xcur xcor
              set ycur ycor
            ]
            [
              let destination patch random-xcor random-ycor

              while [ [pcolor] of destination != cyan ]
                [
                  set destination patch random-xcor random-ycor
                ]
              move-to destination

              set xcur xcor
              set ycur ycor
            ]

          ]

  ask fishes with [pcolor = gray]
    [


          ifelse (random-float 1) < 0.95
            [
              let destination patch (x0 + random-normal 0 1) (y0 + random-normal 0 1)

              while [ [pcolor] of destination != gray ]
                [
                  set destination patch (x0 + random-normal 0 1) (y0 + random-normal 0 1)
                ]
              move-to destination

              set xcur xcor
              set ycur ycor
            ]
            [
              let destination patch random-xcor random-ycor

              while [ [pcolor] of destination != gray ]
                [
                  set destination patch random-xcor random-ycor
                ]
              move-to destination

              set xcur xcor
              set ycur ycor
            ]
        ]


end