How does asking an procedure to run in ask patches produce a different output than running the patches as ask patches?

user_18165305 0
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I was working on a NetLogo project for school, when I ran into this issue with my NetLogo code. When I first made the code, I put the procedure death-check in the ask patches command with this being my program:

patches-own [num-live] 

to setup ;;this sets up all of the code
  clear-all
  ask patches [
    if random 100 < percent-alive [
      cell-birth
    ]
  ]
  reset-ticks
end

to go 
  ask patches [
    set num-live count neighbors with [
      pcolor = yellow
    ]
    death-check
  ]
  tick
end

to cell-birth 
  set pcolor yellow
end

to cell-death 
  set pcolor black
end

to death-check 
  if num-live < 2 or num-live > 3 [
    cell-death
  ]
  if num-live = 3 [
  cell-birth
  ]
end

And I got this output

Now if I put the ask patches inside the procedure, it comes out with a different output. Here is what I changed inside the code:

to go 
  ask patches [
    set num-live count neighbors with [
      pcolor = yellow
    ]
  ]
  death-check
  tick
end

to death-check
  ask patches [
    if num-live < 2 or num-live > 3 [
      cell-death
    ]
    if num-live = 3 [
      cell-birth
    ]
  ]
end

With this being the output

What I was wondering was why did this small change make such a big difference for my program?

netlogo
1 Answers

The difference here is that in one instance, you are calling ask twice, whereas in the other you are only calling ask once. Consider two examples, which I'm calling go-1-ask and go-2-ask:

go-1-ask:

to go-1-ask 
  ask patches [
    set num-live count neighbors with [
      pcolor = yellow
    ]
    if num-live < 2 or num-live > 3 [
      cell-death
    ]
    if num-live = 3 [
      cell-birth
    ]
  ]
  tick
end

go-2-ask:

to go-2-ask
  ask patches [
    set num-live count neighbors with [
      pcolor = yellow
    ]
  ]
  ask patches [
    if num-live < 2 or num-live > 3 [
      cell-death
    ]
    if num-live = 3 [
      cell-birth
    ]
  ]
  tick
end

All I've done relative to your code is nest the code from each different death-check examples within the go procedure.

In go-1-ask, you are asking all patches, in a random order, to set num-live then to evaluate it. So, patch 43 will run the code, then maybe patch 71, and so on. In contrast, in go-2-ask, you are first asking all patches to assess their num-live. Only then, once all patches have performed that first check, are you performing the death-check. In short- the order of operations is different between the two methods, which accounts for the difference in behaviour.

user_55930660
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