css600transp_old.nlogo

turtles-own [energy]

to setup
  clear-all
  setup-patches
  setup-turtles
  reset-ticks
end

to go
  if ticks >= 500 [ stop ]
  move-turtles
  eat-grass
  check-death
  reproduce
  regrow-grass
  tick
end

to move-turtles
  ask turtles [
    right random 360
    forward 1
    check-for-collision  energy
    set energy energy - 1
  ]
end

to check-for-collision  [ ref-energy ]
  if count other turtles-here = 1
  [
    let candidate one-of other turtles-here with
      [who < [who] of myself]
    if (candidate != nobody) [
      ask candidate [
        if ( energy < ref-energy )
           [
             die
           ]
      ]
    ]
  ]
end


to eat-grass
  ask turtles [
    if pcolor = green [
      set pcolor black
      set energy (energy + energy-from-grass)
    ]
    ifelse show-energy?
      [ set label energy ]
      [ set label "" ]
  ]
end

to setup-patches
  ask patches [ set pcolor green ]
end

to setup-turtles
  create-turtles turtle-number [ setxy random-xcor random-ycor ]
end

to reproduce
  ask turtles [
    if energy > birth-energy [
      set energy energy - birth-energy
      hatch 1 [ set energy birth-energy ]
    ]
  ]
end

to check-death
  ask turtles [
    if energy <= 0 [ die ]
  ]
end

to regrow-grass
  ask patches [
    if random 100 < 3 [ set pcolor green ]
  ]
end
@#$#@#$#@
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PLOT
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turtle and grass totals
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"" ""
PENS
"turtles" 1.0 0 -16777216 true "" "plot count turtles"
"grass" 1.0 0 -14439633 true "" "plot count patches with [pcolor = green]"

SLIDER
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turtle-number
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HORIZONTAL

SLIDER
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SLIDER
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birth-energy
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@#$#@#$#@
## WHAT IS IT?

This model shows an ecosystem of turtles and grass and how they relate.

## HOW IT WORKS

Turtle wander about, try to consume grass, reproduce if possible, and die if their energy is insufficient.

## HOW TO USE IT

Adjust the sliders, click 'reset' to prime the model, and 'go' to run it for the default ticks.

## THINGS TO NOTICE

The turtles cut into the grass supply, an reproduce, and will reach an equilibrium. 

## THINGS TO TRY

Adjust the sliders and try to make the number of turtles and grass squares equal at the equilibrium.

The equilibrium is a lot closer with the crude collision detection in place that kills the weaker turtles off

## EXTENDING THE MODEL

The interesting wrinkle I experimented with was collision detection, from code found at Ref(2) below.

We now add:
============
to move-turtles
  ask turtles [
    right random 360
    forward 1
    check-for-collision  energy ;; new call 
    set energy energy - 1
  ]
end

to check-for-collision  [ ref-energy ]
  if count other turtles-here = 1
  [
    let candidate one-of other turtles-here with
      [who < [who] of myself]
    if (candidate != nobody) [
      ask candidate [
        if ( energy < ref-energy ) 
           [
             die
           ]
      ]
    ]
  ]
end


## NETLOGO FEATURES

The turtles-here is interesting. The Logo language syntax feels like Lisp had a tryst with JavaScript but didn't want to talk about it.

## RELATED MODELS

This has Tutorial #3 as its starting point.

## CREDITS AND REFERENCES

1. "NetLogo 6.1.1/app/docs/index.html"
2. http://rocs.hu-berlin.de/statphysw1314/materials/downloads-6/files/GasLab%20Two%20Gas.nlogo
@#$#@#$#@
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@#$#@#$#@
NetLogo 6.1.1
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