---netlogo.nlogo

NETLOGO

mean values-from doves [ minimum-separation ]
3
1

MONITOR
130
425
196
474
max-align
mean values-from doves [ max-align-turn ]
3
1

MONITOR
13
478
93
527
max-cohere
mean values-from doves [ max-cohere-turn ]
3
1

MONITOR
96
479
158
528
max-sep
mean values-from doves [ max-separate-turn ]
3
1

MONITOR
11
529
86
578
normspeed
mean values-from doves [ normal-speed ]
3
1

MONITOR
104
583
166
632
danger-r
mean values-from doves [ danger-sensing-radius ]
3
1

MONITOR
10
583
99
632
escape-angle
mean values-from doves [ escape-angle ]
3
1

MONITOR
90
530
147
579
boost
mean values-from doves [ boost-speed ]
3
1

SLIDER
739
53
911
86
initial-energy
initial-energy
0
100
30
1
1
NIL

SLIDER
739
88
911
121
cruise-speed-mrate
cruise-speed-mrate
0
2
0.0
0.1
1
NIL

SLIDER
739
122
911
155
hunt-speed-mrate
hunt-speed-mrate
0
2
0.0
0.1
1
NIL

SLIDER
737
158
913
191
prey-sensing-radius-mrate
prey-sensing-radius-mrate
0
2
0.1
0.1
1
NIL

MONITOR
873
202
932
251
c-speed
mean values-from hawks [ cruise-speed ]
3
1

MONITOR
807
203
867
252
h-speed
mean values-from hawks [ hunt-speed ]
3
1

MONITOR
742
203
801
252
p-radius
mean values-from hawks [ prey-sensing-radius  ]
3
1

PLOT
738
257
938
407
hawk-life
NIL
NIL
0.0
10.0
0.0
10.0
true
false
PENS
"average" 1.0 0 -16777216 true
"min" 1.0 0 -16776961 true
"max" 1.0 0 -65536 true

@#$#@#$#@
WHAT IS IT?
-----------
This model is an attempt to mimic the flocking of birds.  (The resulting motion also resembles schools of fish.)  The flocks that appear in this model are not created or led in any way by special leader birds.  Rather, each bird is following exactly the same set of rules, from which flocks emerge.

The birds follow three rules: "alignment", "separation", and "cohesion".  "Alignment" means that a bird tends to turn so that it is moving in the same direction that nearby birds are moving.  "Separation" means that a bird will turn to avoid another bird which gets too close.  "Cohesion" means that a bird will move towards other nearby birds (unless another bird is too close).  When two birds are too close, the "separation" rule overrides the other two, which are deactivated until the minimum separation is achieved.

The three rules affect only the bird's heading.  Each bird always moves forward at the same constant speed.


HOW TO USE IT
-------------
First, determine the number of birds you want in the simulation and set the POPULATION slider to that value.  Press SETUP to create the birds, and press GO to have them start flying around.

The default settings for the sliders will produce reasonably good flocking behavior.  However, you can play with them to get variations:

Three TURN-ANGLE sliders control the maximum angle a bird can turn as a result of each rule.

VISION is the distance that each bird can see 360 degrees around it.


THINGS TO NOTICE
----------------
Central to the model is the observation that flocks form without a leader.

There are no random numbers used in this model, except to position the birds initially.  The fluid, lifelike behavior of the birds is produced entirely by deterministic rules.

Also, notice that each flock is dynamic.  A flock, once together, is not guaranteed to keep all of its members.  Why do you think this is?

After running the model for a while, all of the birds have approximately the same heading.  Why?

Sometimes a bird breaks away from its flock.  How does this happen?  You may need to slow down the model or run it step by step in order to observe this phenomenon.


THINGS TO TRY
-------------
Play with the sliders to see if you can get tighter flocks, looser flocks, fewer flocks, more flocks, more or less splitting and joining of flocks, more or less rearranging of birds within flocks, etc.

You can turn off a rule entirely by setting that rule's angle slider to zero.  Is one rule by itself enough to produce at least some flocking?  What about two rules?  What's missing from the resulting behavior when you leave out each rule?

Will running the model for a long time produce a static flock?  Or will the birds never settle down to an unchanging formation?  Remember, there are no random numbers used in this model.


EXTENDING THE MODEL
-------------------
Currently the birds can "see" all around them.  What happens if birds can only see in front of them?

Is there some way to get V-shaped flocks, like migrating geese?

What happens if you put walls around the edges of the screen that the birds can't fly into?

Can you get the birds to fly around obstacles in the middle of the screen?

What would happen if you gave the birds different velocities?  For example, you could make birds that are not near other birds fly faster to catch up to the flock.  Or, you could simulate the diminished air resistance that birds experience when flying together by making them fly faster when in a group.

Are there other interesting ways you can make the birds different from each other?  There could be random variation in the population, or you could have distinct "species" of bird.


NETLOGO FEATURES
----------------
Notice the need for the SUBTRACT-HEADINGS primitive and special procedure for averaging groups of headings.  Just subtracting the numbers, or averaging the numbers, doesn't give you the results you'd expect, because of the discontinuity where headings wrap back to 0 once they reach 360.


CREDITS AND REFERENCES
----------------------
This model is inspired by the Boids simulation invented by Craig Reynolds.  The algorithm we use here is roughly similar to the original Boids algorithm, but it is not the same.  The exact details of the algorithm tend not to matter very much -- as long as you have alignment, separation, and cohesion, you will usually get flocking behavior resembling that produced by Reynolds' original model.  Information on Boids is available at http://www.red3d.com/cwr/boids/.

To refer to this model in academic publications, please use: Wilensky, U. (1998).  NetLogo Flocking model. http://ccl.northwestern.edu/netlogo/models/Flocking. 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/Flocking for terms of use.
@#$#@#$#@
default
true
0
Polygon -7566196 true true 150 5 40 250 150 205 260 250

airplane
true
0
Polygon -7566196 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15

arrow
true
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Polygon -7566196 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150

box
false
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Polygon -7566196 true true 150 285 285 225 285 75 150 135
Polygon -7566196 true true 150 135 15 75 150 15 285 75
Polygon -7566196 true true 15 75 15 225 150 285 150 135
Line -16777216 false 150 285 150 135
Line -16777216 false 150 135 15 75
Line -16777216 false 150 135 285 75

bug
true
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Circle -7566196 true true 96 182 108
Circle -7566196 true true 110 127 80
Circle -7566196 true true 110 75 80
Line -7566196 true 150 100 80 30
Line -7566196 true 150 100 220 30

butterfly
true
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Polygon -7566196 true true 150 165 89 198 75 225 75 255 105 270 135 255 150 240
Polygon -7566196 true true 139 148 100 105 55 90 25 90 10 105 10 135 25 180 40 195 85 194 139 163
Polygon -7566196 true true 162 150 200 105 245 90 275 90 290 105 290 135 275 180 260 195 215 195 162 165
Polygon -16777216 true false 150 255 135 225 120 150 135 120 150 105 165 120 180 150 165 225
Circle -16777216 true false 135 90 30
Line -16777216 false 150 105 195 60
Line -16777216 false 150 105 105 60

car
false
0
Polygon -7566196 true true 300 180 279 164 261 144 240 135 226 132 213 106 203 84 185 63 159 50 135 50 75 60 0 150 0 165 0 225 300 225 300 180
Circle -16777216 true false 180 180 90
Circle -16777216 true false 30 180 90
Polygon -16777216 true false 162 80 132 78 134 135 209 135 194 105 189 96 180 89
Circle -7566196 true true 47 195 58
Circle -7566196 true true 195 195 58

circle
false
0
Circle -7566196 true true 30 30 240

circle 2
false
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Circle -16777216 true false 46 46 210

cow
false
0
Polygon -7566196 true true 200 193 197 249 179 249 177 196 166 187 140 189 93 191 78 179 72 211 49 209 48 181 37 149 25 120 25 89 45 72 103 84 179 75 198 76 252 64 272 81 293 103 285 121 255 121 242 118 224 167
Polygon -7566196 true true 73 210 86 251 62 249 48 208
Polygon -7566196 true true 25 114 16 195 9 204 23 213 25 200 39 123

face happy
false
0
Circle -7566196 true true 8 8 285
Circle -16777216 true false 60 75 60
Circle -16777216 true false 180 75 60
Polygon -16777216 true false 150 255 90 239 62 213 47 191 67 179 90 203 109 218 150 225 192 218 210 203 227 181 251 194 236 217 212 240

face neutral
false
0
Circle -7566196 true true 8 7 285
Circle -16777216 true false 60 75 60
Circle -16777216 true false 180 75 60
Rectangle -16777216 true false 60 195 240 225

face sad
false
0
Circle -7566196 true true 8 8 285
Circle -16777216 true false 60 75 60
Circle -16777216 true false 180 75 60
Polygon -16777216 true false 150 168 90 184 62 210 47 232 67 244 90 220 109 205 150 198 192 205 210 220 227 242 251 229 236 206 212 183

fish
true
0
Polygon -1 true false 131 256 87 279 86 285 120 300 150 285 180 300 214 287 212 280 166 255
Polygon -1 true false 195 165 235 181 218 205 210 224 204 254 165 240
Polygon -1 true false 45 225 77 217 103 229 114 214 78 134 60 165
Polygon -7566196 true true 136 270 77 149 81 74 119 20 146 8 160 8 170 13 195 30 210 105 212 149 166 270
Circle -16777216 true false 106 55 30

flag
false
0
Rectangle -7566196 true true 60 15 75 300
Polygon -7566196 true true 90 150 270 90 90 30
Line -7566196 true 75 135 90 135
Line -7566196 true 75 45 90 45

flower
false
0
Polygon -11352576 true false 135 120 165 165 180 210 180 240 150 300 165 300 195 240 195 195 165 135
Circle -7566196 true true 85 132 38
Circle -7566196 true true 130 147 38
Circle -7566196 true true 192 85 38
Circle -7566196 true true 85 40 38
Circle -7566196 true true 177 40 38
Circle -7566196 true true 177 132 38
Circle -7566196 true true 70 85 38
Circle -7566196 true true 130 25 38
Circle -7566196 true true 96 51 108
Circle -16777216 true false 113 68 74
Polygon -11352576 true false 189 233 219 188 249 173 279 188 234 218
Polygon -11352576 true false 180 255 150 210 105 210 75 240 135 240

house
false
0
Rectangle -7566196 true true 45 120 255 285
Rectangle -16777216 true false 120 210 180 285
Polygon -7566196 true true 15 120 150 15 285 120
Line -16777216 false 30 120 270 120

leaf
false
0
Polygon -7566196 true true 150 210 135 195 120 210 60 210 30 195 60 180 60 165 15 135 30 120 15 105 40 104 45 90 60 90 90 105 105 120 120 120 105 60 120 60 135 30 150 15 165 30 180 60 195 60 180 120 195 120 210 105 240 90 255 90 263 104 285 105 270 120 285 135 240 165 240 180 270 195 240 210 180 210 165 195
Polygon -7566196 true true 135 195 135 240 120 255 105 255 105 285 135 285 165 240 165 195

line
true
0
Line -7566196 true 150 0 150 300

pentagon
false
0
Polygon -7566196 true true 150 15 15 120 60 285 240 285 285 120

person
false
0
Circle -7566196 true true 110 5 80
Polygon -7566196 true true 105 90 120 195 90 285 105 300 135 300 150 225 165 300 195 300 210 285 180 195 195 90
Rectangle -7566196 true true 127 79 172 94
Polygon -7566196 true true 195 90 240 150 225 180 165 105
Polygon -7566196 true true 105 90 60 150 75 180 135 105

plant
false
0
Rectangle -7566196 true true 135 90 165 300
Polygon -7566196 true true 135 255 90 210 45 195 75 255 135 285
Polygon -7566196 true true 165 255 210 210 255 195 225 255 165 285
Polygon -7566196 true true 135 180 90 135 45 120 75 180 135 210
Polygon -7566196 true true 165 180 165 210 225 180 255 120 210 135
Polygon -7566196 true true 135 105 90 60 45 45 75 105 135 135
Polygon -7566196 true true 165 105 165 135 225 105 255 45 210 60
Polygon -7566196 true true 135 90 120 45 150 15 180 45 165 90

spider
true
0
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Line -7566196 true 167 109 170 90
Line -7566196 true 170 91 156 88
Line -7566196 true 130 91 144 88
Line -7566196 true 133 109 130 90
Polygon -7566196 true true 167 117 207 102 216 71 227 27 227 72 212 117 167 132
Polygon -7566196 true true 164 210 158 194 195 195 225 210 195 285 240 210 210 180 164 180
Polygon -7566196 true true 136 210 142 194 105 195 75 210 105 285 60 210 90 180 136 180
Polygon -7566196 true true 133 117 93 102 84 71 73 27 73 72 88 117 133 132
Polygon -7566196 true true 163 140 214 129 234 114 255 74 242 126 216 143 164 152
Polygon -7566196 true true 161 183 203 167 239 180 268 239 249 171 202 153 163 162
Polygon -7566196 true true 137 140 86 129 66 114 45 74 58 126 84 143 136 152
Polygon -7566196 true true 139 183 97 167 61 180 32 239 51 171 98 153 137 162

square
false
0
Rectangle -7566196 true true 30 30 270 270

square 2
false
0
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Rectangle -16777216 true false 60 60 240 240

star
false
0
Polygon -7566196 true true 60 270 150 0 240 270 15 105 285 105
Polygon -7566196 true true 75 120 105 210 195 210 225 120 150 75

target
false
0
Circle -7566196 true true 0 0 300
Circle -16777216 true false 30 30 240
Circle -7566196 true true 60 60 180
Circle -16777216 true false 90 90 120
Circle -7566196 true true 120 120 60

tree
false
0
Circle -7566196 true true 118 3 94
Rectangle -6524078 true false 120 195 180 300
Circle -7566196 true true 65 21 108
Circle -7566196 true true 116 41 127
Circle -7566196 true true 45 90 120
Circle -7566196 true true 104 74 152

triangle
false
0
Polygon -7566196 true true 150 30 15 255 285 255

triangle 2
false
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Polygon -16777216 true false 151 99 225 223 75 224

truck
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Polygon -7566196 true true 296 193 296 150 259 134 244 104 208 104 207 194
Rectangle -1 true false 195 60 195 105
Polygon -16777216 true false 238 112 252 141 219 141 218 112
Circle -16777216 true false 234 174 42
Rectangle -7566196 true true 181 185 214 194
Circle -16777216 true false 144 174 42
Circle -16777216 true false 24 174 42
Circle -7566196 false true 24 174 42
Circle -7566196 false true 144 174 42
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turtle
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Polygon -11352576 true false 105 90 75 75 55 75 40 89 31 108 39 124 60 105 75 105 90 105
Polygon -11352576 true false 132 85 134 64 107 51 108 17 150 2 192 18 192 52 169 65 172 87
Polygon -11352576 true false 85 204 60 233 54 254 72 266 85 252 107 210
Polygon -7566196 true true 119 75 179 75 209 101 224 135 220 225 175 261 128 261 81 224 74 135 88 99

wheel
false
0
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Line -7566196 true 150 285 150 15
Line -7566196 true 15 150 285 150
Circle -7566196 true true 120 120 60
Line -7566196 true 216 40 79 269
Line -7566196 true 40 84 269 221
Line -7566196 true 40 216 269 79
Line -7566196 true 84 40 221 269

x
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0
Polygon -7566196 true true 270 75 225 30 30 225 75 270
Polygon -7566196 true true 30 75 75 30 270 225 225 270

@#$#@#$#@
NetLogo 2.1.0
@#$#@#$#@
set population 200
setup
repeat 200 [ go ]
@#$#@#$#@
@#$#@#$#@