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view/download model file: Ant-Foraging.nlogo
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.
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 nest-scent in a red-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 and nest scent. There is an on-off PLOT? switch. Turning off the plotting lets the model run faster.
The DISPLAY-FIELD chooser determines whether to display the chemical concentration or the nest-scent concentration.
The MAKE BARRIER button allows barriers to be drawn, which block the ants and diffusion of the chemical and nest scent. The REMOVE BARRIER allows some or all of the barriers to be erased. Click or hold the mouse button to draw or erase barriers.
The DEPOSIT FOOD button allows more food to be deposited. The kind of food to be deposited (“cyan,” “sky,” or “blue”) is determined by the FOOD-KIND chooser. Click or hold the mouse button to add food in particular places.
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 world. In BLUE you see food2 which is on the lower left of the world. In MAGENTA you see food3 which is on the upper left of the world.
Try creating a barrier between a food source and the nest. How long does it take the ants to create a path around it? If you make a hole through the barrier (with REMOVE BARRIER), how long does it take the ants to discover it?
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.
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.
Modified 2007-10-08 by B.J. MacLennan to simulate diffusion of nest-scent, to allow display of nest-scent, to allow insertion and removal of barriers, and to allow introduction of more food.
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, 2001, 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 Uri Wilensky. All rights reserved. See http://ccl.northwestern.edu/netlogo/models/Ants for terms of use.
globals [
carrying-color
free-color
nest-xcor
nest-ycor
barrier-width
barrier-height
barrier-depth
]
turtles-own [
carrying-food?
drop-size ;; how much chemical we're currently dropping
]
patches-own [
chemical
food
nest?
nest-scent
food-source-number
barrier?
]
to startup
set free-color brown
set carrying-color red
set nest-xcor 0.7 * min-pxcor
set nest-ycor 0
set barrier-width 0.1 * world-width
set barrier-height 0.4 * max-pycor
set barrier-depth 0.2 * min-pycor
end
;;;;;;;;;;;;;;;;;;;;;;;;
;;; Setup Procedures ;;;
;;;;;;;;;;;;;;;;;;;;;;;;
to setup
cp ct
setup-turtles
setup-patches
reset-ticks
clear-all-plots
do-plotting
end
to setup-turtles
set-default-shape turtles "bug"
crt ants [
set size 2 ;; easier to see this way
rt random-float 360
set color free-color
set carrying-food? false
setxy nest-xcor nest-ycor
]
end
to setup-patches
ask patches [
set chemical 0
set food 0
set food-source-number -1
set barrier? false
setup-nest
setup-food
setup-barriers
update-display
]
repeat 100 [diffuse nest-scent diffusion-rate / 100]
end
to setup-nest ;; patch procedure
;; set nest? variable to true inside the nest
ifelse (distancexy nest-xcor nest-ycor) < 5
[ set nest? true
set nest-scent 1000 ]
[ set nest? false ]
end
to setup-food ;; patch procedure
;; setup one food source on the right
if ((distancexy (0.7 * max-pxcor) 0) < 5)
[ set food-source-number 1 ]
;; set "food" at sources to either 1 or 2
if (food-source-number > 0)
[ set food (1 + random 2) ]
end
to setup-barriers ;; patch procedure
set barrier? ((abs pxcor) < barrier-width) and (barrier-depth < pycor) and (pycor < barrier-height)
; ifelse ((abs pxcor) < barrier-width) and (barrier-depth < pycor) and (pycor < barrier-height))
end
to update-display ;; patch procedure
;; give color to nest and food sources
ifelse nest?
[ set pcolor violet ] [
ifelse barrier?
[ set pcolor grey ] [
ifelse (food > 0)
[ if (food-source-number = 1) [ set pcolor cyan ]
if (food-source-number = 2) [ set pcolor sky ]
if (food-source-number = 3) [ set pcolor blue ]
] [
ifelse display-field = "chemical"
[set pcolor scale-color green chemical 0.1 5 ] ;; scale color to show chemical concentration
[set pcolor scale-color red (log (nest-scent + 0.1) 10) -1 3 ] ;; scale color to show nest scent
]]]
end
;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Runtime Procedures ;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;
to go ;; forever button
ask turtles [ go-turtles ]
diffuse chemical (diffusion-rate / 100)
diffuse nest-scent (diffusion-rate / 100)
ask patches [ go-patches ]
tick
do-plotting
end
to go-turtles ;; turtle procedure
if (who < ticks) ;; delay the initial departure of ants
[ ifelse carrying-food?
[set color carrying-color return-to-nest ] ;; if ant finds food, it returns to the nest
[set color free-color look-for-food ] ;; otherwise it keeps looking
; [set color orange return-to-nest ] ;; if ant finds food, it returns to the nest
; [set color brown look-for-food ] ;; otherwise it keeps looking
avoid-barrier
]
end
to go-patches ;; patch procedure
set chemical (chemical * (100 - evaporation-rate) / 100) ;;slowly evaporate chemical
if barrier? [set chemical 0 set nest-scent 0]
ifelse nest?
[ set nest-scent 1000 ]
[ set nest-scent nest-scent * 0.99 ]
if food-source-number > 0
[ set food food + replenish-rate ]
update-display ;; Refresh the Display
end
to return-to-nest ;; turtle procedure
ifelse nest? ;; if ant is in the nest, it drops food and heads out again
[ set carrying-food? false
rt 180 fd 1
]
[ set chemical (chemical + drop-size) ;; drop some chemical, but the amount decreases each time
set drop-size (drop-size - 1.5)
if drop-size < 1 [set drop-size 1]
uphill-nest-scent ;; head toward the greatest value of nest-scent
wiggle ;; which is toward the nest
fd 1]
end
to look-for-food ;; turtle procedure
if (food > 0)
[ set carrying-food? true ;; pick up food
set food food - 1 ;; and reduce the food source
set drop-size 60
rt 180 stop ;; and turn around
]
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 ;; turtle procedure
wiggle
;; sniff left and right, and go where the strongest smell is
let scent-ahead [chemical] of patch-ahead 1
let scent-right chemical-scent 45
let scent-left chemical-scent -45
if (scent-right > scent-ahead) or (scent-left > scent-ahead)
[ ifelse scent-right > scent-left
[ rt 45 ]
[ lt 45 ]
]
end
to uphill-nest-scent ;; turtle procedure
wiggle
;; sniff left and right, and go where the strongest smell is
let scent-ahead [nest-scent] of patch-ahead 1
let scent-right get-nest-scent 45
let scent-left get-nest-scent -45
if (scent-right > scent-ahead) or (scent-left > scent-ahead)
[ ifelse scent-right > scent-left
[ rt 45 ]
[ lt 45 ]
]
end
to wiggle ;; turtle procedure
rt random 40 - random 40
if not can-move? 1
[ rt 180 ]
end
to-report get-nest-scent [ angle ]
let p patch-right-and-ahead angle 1
if p = nobody [ report 0 ]
report [nest-scent] of p
end
to-report chemical-scent [ angle ]
let p patch-right-and-ahead angle 1
if p = nobody [ report 0 ]
report [chemical] of p
end
to avoid-barrier
if (nobody != patch-ahead 1) and ([barrier?] of patch-ahead 1)
[right 90 + random 180]
forward 1
end
to do-plotting
if not plot? [ stop ]
set-current-plot "Food of each kind"
set-current-plot-pen "food-in-pile1"
plot count patches with [pcolor = cyan]
set-current-plot-pen "food-in-pile2"
plot count patches with [pcolor = sky]
set-current-plot-pen "food-in-pile3"
plot count patches with [pcolor = blue]
end
to make-barrier
if mouse-down?
[ask patches [
if ((abs (pxcor - mouse-xcor)) < 2) and ((abs (pycor - mouse-ycor)) < 2)
[set pcolor grey
set barrier? true]]
]
end
to remove-barrier
if mouse-down?
[ask patches [
if ((abs (pxcor - mouse-xcor)) < 2) and ((abs (pycor - mouse-ycor)) < 2)
[set pcolor black
set barrier? false]
update-display
]
]
end
to deposit-food
if mouse-down?
[ask patches [
if ((abs (pxcor - mouse-xcor)) < 2) and ((abs (pycor - mouse-ycor)) < 2)
[ set food-source-number 1 + position food-kind ["cyan" "sky" "blue"]
set food (1 + random 2) ]
update-display
]
]
end
; Miscellaneous cleanups by B. MacLennan, 2011-12-30.
;
; *** NetLogo 3.1.4 Model Copyright Notice ***
;
; This model was created as part of the project: CONNECTED MATHEMATICS:
; MAKING SENSE OF COMPLEX PHENOMENA THROUGH BUILDING OBJECT-BASED PARALLEL
; MODELS (OBPML). The project gratefully acknowledges the support of the
; National Science Foundation (Applications of Advanced Technologies
; Program) -- grant numbers RED #9552950 and REC #9632612.
;
; Copyright 1998 by Uri Wilensky. All rights reserved.
;
; Permission to use, modify or redistribute this model is hereby granted,
; provided that both of the following requirements are followed:
; a) this copyright notice is included.
; b) this model will not be redistributed for profit without permission
; from Uri Wilensky.
; Contact Uri Wilensky for appropriate licenses for redistribution for
; profit.
;
; This model was converted to NetLogo as part of the projects:
; PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING
; IN CLASSROOMS and/or INTEGRATED SIMULATION AND MODELING ENVIRONMENT.
; The project gratefully acknowledges the support of the
; National Science Foundation (REPP & ROLE programs) --
; grant numbers REC #9814682 and REC-0126227.
; Converted from StarLogoT to NetLogo, 2001.
;
; 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 Uri Wilensky. All rights reserved.
; See http://ccl.northwestern.edu/netlogo/models/Ants
; for terms of use.
;
; *** End of NetLogo 3.1.4 Model Copyright Notice ***
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