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Aruho
Aruho

Reputation: 1

NetLogo: Having a turtle remember its starting location

I want to have my turtles move back and forth between a central area and their starting location. I have set the central area (patch 0 0, and its neighbouring patches). I have set these turtles to begin from random locations on setup.

Now I need them to move to the central area and be able to remember and return to their respective starting positions. Here is my attempt, but one that is not working.

ask patches
[ set target-patch patch 0 0  
  ask target-patch
  [ set pcolor green
    ask neighbors [set pcolor green]
    set hold-time 5
  ]
]

create-turtles 10
[ set shape "car"
  set size 1
  set color white
  setxy random-xcor random-ycor
  if (patches != patches with [pcolor = green])
  [ set start-position (random-xcor random-ycor)] ;; line with error
]

to go
  ask turtles
  [ set heading target-patch move-to target-patch
    set hold-time hold-time + 5
  ]
  ask turtles
  [ if hold-time >= 10
    [ set heading start-position move-to start-position]
  ]
end

Upvotes: 0

Views: 598

Answers (1)

JenB
JenB

Reputation: 17678

There are several problems with your code. I strongly suggest that you code in smaller pieces. That is, add some code and make sure it works before writing the next piece. Making sure it works is not just making it through without error messages, it needs to do what you expect it to do.

On your specific question. The line if (patches != patches with [pcolor = green]) is causing an error. First, patches is the set of all patches, not just a particular patch. So you are (sort of) asking whether the set of all patches is not equal to the set of patches that are green. Is that really what you intended? If so, it is easier to simply ask whether there is any patch that is not green:

if any? patches with [pcolor != green]

or to check whether they are all green and continue if not:

if not all? patches [pcolor = green]

However, since you are asking about moving back and forth to and from the central green patches, I think you really want to have the turtle check whether the patch they happen to be located on is green. This code looks at the patch where the turtle is located (patch-here) and checks whether the color (pcolor) is green:

if [pcolor] of patch-here = green [ ]

However, one of the tricks of NetLogo is that turtles can access the variables of the patch they are on directly. Note that a patch cannot access a turtle's variables because there may be multiple turtles on the patch so the patch doesn't know which turtle you want. But a turtle can only ever be on one patch at once. So you could write:

if pcolor = green [ ]

You also need to rethink this code:

ask patches
[ set target-patch patch 0 0  
  ask target-patch
  [ set pcolor green
    ask neighbors [set pcolor green]
    set hold-time 5
  ]
]

This suggests to me that you have misunderstood something very fundamental to NetLogo programming. You need to think from the perspective of an individual agent. Looking at this code, you first do ask turtles, so that is going to run through all the turtles in random order. Let's call them A, then B, then C and so on.

What is each turtle going to do? Everything in the [ ]. So, A sets the value of the global variable named "target-patch" to patch 0 0. Then A asks that patch to turn green, have the 8 surrounding patches to turn green, and to set the variable "hold-time" to the value 5.

So far, so good. But then turtle B does exactly the same thing - it assigns "target-patch", turns it and its neighbors green etc. Then turtle C. If you have 100 turtles, this block of code will run 100 times and do exactly the same thing each time.

Upvotes: 1

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