globals [
  clock  ;; used to prevent chemical from wrapping around edges of screen
]
turtles-own [
  carrying-food?
]
patches-own [
  chemical food nest? nest-scent food-source-number
]

to setup
  ca
  setup-turtles
  setup-patches
  set clock 0
  do-plotting
end

to setup-turtles
  set-default-shape turtles "hawk"
  cct vultures [
    set size 3 
    set color red
    set carrying-food? false
    setxy random-float screen-edge-x
          random-float screen-edge-y
  ]
end

to setup-patches
    ask patches [
    set chemical 0
    set food 0
    set food-source-number -1
    setup-nest
    setup-food
    update-display
  ]
end

to setup-nest  
  set nest? ((distancexy 0 0) < 5)
  set nest-scent (200 - (distancexy 0 0))
end

to setup-food  
  if ((distancexy -10 -10) < food-size)
  [ set food-source-number 1 ]
  if (food-source-number > 0)
  [ set food 1 ]
end

to update-display  
  ifelse (food > 0)
     [if (food-source-number = 1) [ set pcolor blue ]]
     [set pcolor scale-color green chemical 0.1 5]
end

to go 
  ask turtles [go-turtles]
  ask patches [update-display]
  do-plotting
  set clock (clock + 1)
end

to go-turtles  
  if (who < clock)  
  [ifelse carrying-food?
    [set color orange look-for-food]  
    [set color red look-for-food]  
  ]
end

to look-for-food  ;; turtle procedure
  if (food > 0)
  [ set carrying-food? true
    set food (food - 1)      
    rt 180 stop         
  ]
  ifelse (chemical > 2)
  [ fd 1 ]
  [ ifelse (chemical < 0.05) ;; go in the direction where the chemical smell is strongest
    [ wiggle fd 1]
    [ uphill-chemical fd 1]
  ]
end

to uphill-chemical  
  wiggle
  let scent-ahead food-of patch-ahead 2
  let scent-right food-of patch-right-and-ahead 45 2
  let scent-left food-of patch-left-and-ahead 45 2
  if ((scent-right > scent-ahead) or (scent-left > scent-ahead))
    [ ifelse (scent-right > scent-left)
      [ rt 45 ]
      [ lt 45 ]
  ]
end

to wiggle 
  rt random 30 - random 30
end

to do-plotting
  if not plot? [ stop ]
  set-current-plot "Amount of Food"
  set-current-plot-pen "food"
  plot count patches with [pcolor = blue]
end
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@#$#@#$#@
WHAT IS IT?
-----------
In this project, a colony of ants forages for food. Each ant follows a set of simple rules, but the colony as a whole acts in a sophisticated way.

When an ant finds a piece of food, it carries the food back to the nest, dropping a chemical as it moves. When other ants "sniff" the chemical, they follow the chemical toward the food. As more ants carry food to the nest, they reinforce the chemical trail.


HOW TO USE IT
-------------
Click the SETUP button to set up the ant nest (in violet, at center) and three piles of food. Click the GO button to start the simulation. The chemical is shown in a green-to-white gradient.

The EVAPORATION-RATE slider controls the evaporation rate of the chemical. The DIFFUSION-RATE slider controls the diffusion rate of the chemical. There is an on-off PLOT? switch.  Turning off the plotting lets the model run faster.


THINGS TO NOTICE
----------------
The ant colony generally exploits the food source in order, starting with the food closest to the nest, and finishing with the food most distant from the nest. It is more difficult for the ants to form a stable trail to the more distant food, since the chemical trail has more time to evaporate and diffuse before being reinforced.

Once the colony finishes collecting the closest food, the chemical trail to that food naturally disappears, freeing up ants to help collect the other food sources. The more distant food sources require a larger "critical number" of ants to form a stable trail.

The consumption of the food source is shown in a plot. In CYAN you see food1 which is on the right side of the screen. In BLUE you see food2 which is on the lower left of the screen.  In MAGENTA you see food3 which is on the upper left of the screen.


EXTENDING THE MODEL
-------------------
Try different placements for the food sources. What happens if two food sources are equidistant from the nest? When that happens in the real world, ant colonies typically exploit one source then the other (not at the same time).

In this project, the ants use a "trick" to find their way back to the nest: they follow the "nest scent." Real ants use a variety of different approaches to find their way back to the nest. Try to implement some alternative strategies.


NETLOGO FEATURES
-------------------
In the UPHILL-CHEMICAL procedure, the ant "follows the gradient" of the chemical. That is, it "sniffs" in three directions, then turns in the direction where the chemical is strongest. You might want to try variants of the UPHILL-CHEMICAL procedure, changing the number and placement of "ant sniffs."

RETURN-TO-NEST uses a similar gradient.


CREDITS AND REFERENCES
-----------------------
This model was developed at the MIT Media Lab. See Resnick, M. (1994) "Turtles, Termites and Traffic Jams: Explorations in Massively Parallel Microworlds." Cambridge, Ma: MIT Press. Adapted to StarLogoT, 1997, as part of the Connected Mathematics Project. Adapted to NetLogo, 2000, as part of the Participatory Simulations Project.

To refer to this model in academic publications, please use: Wilensky, U. (1998).  NetLogo Ants model. http://ccl.northwestern.edu/netlogo/models/Ants. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

In other publications, please use: Copyright 1998 by Uri Wilensky.  All rights reserved.  See http://ccl.northwestern.edu/netlogo/models/Ants for terms of use.
@#$#@#$#@
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NetLogo 3.0.2
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