# Flocking Benchmark

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Model was written in NetLogo 4.1pre9
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globals [ result ] turtles-own [ flockmates ;; agentset of nearby turtles nearest-neighbor ;; closest one of our flockmates ] to benchmark random-seed 5454 reset-timer setup repeat 700 [ go ] set result timer end to setup ca cro population [ set color yellow - 2 + random 7 ;; random shades look nice setxy (random-float world-width) (random-float world-height) rt random-float 360 ] end to go ask turtles [ flock ] tick end to flock ;; turtle procedure find-flockmates if any? flockmates [ find-nearest-neighbor ifelse distance nearest-neighbor < minimum-separation [ separate ] [ align cohere ] ] fd 1 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. report atan mean [sin heading] of flockmates mean [cos heading] 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 (my-subtract-headings new-heading heading) max-turn end to turn-away [new-heading max-turn] ;; turtle procedure turn-at-most (my-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 ;; To find the difference between two headings, we can't just ;; subtract the numbers, because 0 and 360 are the same heading. ;; For example, the difference between a heading of 5 degrees ;; and a heading of 355 degrees is 10 degrees, not 350 degrees. to-report my-subtract-headings [h1 h2] ifelse abs (h1 - h2) <= 180 [ report h1 - h2 ] [ ifelse h1 > h2 [ report h1 - h2 - 360 ] [ report h1 - h2 + 360 ] ] end

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