Flocking (Perspective Demo)

Flocking (Perspective Demo) preview image

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Uri_dolphin3 Uri Wilensky (Author)

Tags

biology 

Tagged by Reuven M. Lerner about 7 years ago

Model group CCL | Visible to everyone | Changeable by group members (CCL)
Model was written in NetLogo 5.0.4 • Viewed 392 times • Downloaded 32 times • Run 0 times
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Comments and Questions

sum [dx]!! (Question)

what's the utility of sum [dx] in the code?

Posted over 8 years ago

average heading of flock

To compute the average heading of the flock, the x- and y-components of each turtle's direction vector (a unit vector with the same heading as the turtle) are added up and used by the atan function to convert back to an angle. ave-heading = atan sum [dx] of flockmates sum [dy] of flockmates Look up dx, dy in the NL Dictionary.

Posted over 8 years ago

Click to Run Model

turtles-own [
  flockmates         ;; agentset of nearby turtles
  nearest-neighbor   ;; closest one of our flockmates
]

to setup
  clear-all
  crt population
    [ set color yellow - 2 + random 7  ;; random shades look nice
      set size 1.5  ;; easier to see
      setxy random-xcor random-ycor ]
  ask patches
    [ set pcolor green - random 2 ]
  reset-ticks
end 

to go
  ask turtles [ flock ]
  ;; the following line is used to make the turtles
  ;; animate more smoothly.
  repeat 5 [ ask turtles [ fd 0.2 ] display ]
  ;; for greater efficiency, at the expense of smooth
  ;; animation, substitute the following line instead:
  ;;   ask turtles [ fd 1 ]
  tick
end 

to flock  ;; turtle procedure
  find-flockmates
  if any? flockmates
    [ find-nearest-neighbor
      ifelse distance nearest-neighbor < minimum-separation
        [ separate ]
        [ align
          cohere ] ]
end 

to find-flockmates  ;; turtle procedure
  set flockmates other turtles in-radius vision
end 

to find-nearest-neighbor ;; turtle procedure
  set nearest-neighbor min-one-of flockmates [distance myself]
end 

;;; SEPARATE

to separate  ;; turtle procedure
  turn-away ([heading] of nearest-neighbor) max-separate-turn
end 

;;; ALIGN

to align  ;; turtle procedure
  turn-towards average-flockmate-heading max-align-turn
end 

to-report average-flockmate-heading  ;; turtle procedure
  ;; We can't just average the heading variables here.
  ;; For example, the average of 1 and 359 should be 0,
  ;; not 180.  So we have to use trigonometry.
  ;; Theoretically this could fail if both sums are 0
  ;; since atan 0 0 is undefined, but in practice that's
  ;; vanishingly unlikely.
  report atan sum [dx] of flockmates
              sum [dy] of flockmates
end 

;;; COHERE

to cohere  ;; turtle procedure
  turn-towards average-heading-towards-flockmates max-cohere-turn
end 

to-report average-heading-towards-flockmates  ;; turtle procedure
  ;; "towards myself" gives us the heading from the other turtle
  ;; to me, but we want the heading from me to the other turtle,
  ;; so we add 180
  report atan mean [sin (towards myself + 180)] of flockmates
              mean [cos (towards myself + 180)] of flockmates
end 

;;; HELPER PROCEDURES

to turn-towards [new-heading max-turn]  ;; turtle procedure
  turn-at-most (subtract-headings new-heading heading) max-turn
end 

to turn-away [new-heading max-turn]  ;; turtle procedure
  turn-at-most (subtract-headings heading new-heading) max-turn
end 

;; turn right by "turn" degrees (or left if "turn" is negative),
;; but never turn more than "max-turn" degrees

to turn-at-most [turn max-turn]  ;; turtle procedure
  ifelse abs turn > max-turn
    [ ifelse turn > 0
        [ rt max-turn ]
        [ lt max-turn ] ]
    [ rt turn ]
end 


; Copyright 1998 Uri Wilensky.
; See Info tab for full copyright and license.

There are 6 versions of this model.

Uploaded by When Description Download
Uri Wilensky about 7 years ago Updated to NetLogo 5.0.4 Download this version
Uri Wilensky almost 8 years ago Updated version tag Download this version
Uri Wilensky over 8 years ago Updated to NetLogo 5.0 Download this version
Uri Wilensky about 10 years ago Updated from NetLogo 4.1 Download this version
Uri Wilensky about 10 years ago Model from NetLogo distribution Download this version
Uri Wilensky about 10 years ago Flocking (Perspective Demo) Download this version

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