No Friends on a Powder Day?

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Default-person Spencer Murphy (Author)


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  max-snow    ; maximum amount any patch can hold
  ;; create wealth by ability globals to use in histogram

  snow-here      ; the current amount of snow on this patch
  max-snow-here  ; the maximum amount of snow this patch can hold

  soreness         ; how sore a turtle (skier) is, proportional to how long a skier has been skiing
  wealth           ; the amount of fresh snow a skiier has skied
  energy           ; maximum ticks a turtle can ski before they're tired and go home
  ability          ; how fast a skier goes, and proportional to how much snow they destroy
  vision           ; how many patches ahead a skier can see


to setup
  ;; set global variables to appropriate values
  set max-snow 100
  ;; call other procedures to set up various parts of the world

;; set up the initial amounts of snow each patch has

to setup-patches
  ;; give some patches the highest amount of snow possible --
  ;; these patches are the "best terrain"
  ask patches
    [ set max-snow-here 0
      if (random-float 100.0) <= percent-best-land
        [ set max-snow-here max-snow
          set snow-here max-snow-here ] ]
  ;; spread that snow around the window a little and put a little back
  ;; into the patches that are the "best land" found above
  repeat 5
    [ ask patches with [max-snow-here != 0]
        [ set snow-here max-snow-here ]
      diffuse snow-here 0.25 ]
  repeat 10
    [ diffuse snow-here 0.25 ]          ;; spread the snow around some more
  ask patches
    [ set snow-here floor snow-here    ;; round snow levels to whole numbers
      set max-snow-here snow-here      ;; initial snow level is also maximum
      recolor-patch ]

to recolor-patch  ;; patch procedure -- use color to indicate snow level
  set pcolor scale-color white snow-here 0 max-snow

;; set up the initial values for the turtle variables

to setup-turtles
  set-default-shape turtles "person"
  create-turtles num-skiers
    [ move-to one-of patches  ;; put turtles on patch centers
      set size 1.5  ;; easier to see
      set soreness random energy ]

to set-initial-turtle-vars
  set soreness 0
  ;;face one-of neighbors4
  set energy energy-min +
                        random (energy-max - energy-min + 1)
  set ability 1 + random 3
    ;;round ability
  set wealth 0.1  ;; everyone starts the day having skied 0 snow (0.1 to avoid division by zero)
  set vision 1 + random max-vision
  set label ability

;; Set the class of the turtles -- if a turtle has less than a third
;; the wealth of the richest turtle, color it red.  If between one
;; and two thirds, color it green.  If over two thirds, color it blue.

to recolor-turtles
  let max-wealth max [wealth] of turtles
  ask turtles
    [ ifelse (wealth <= max-wealth / 3)
        [ set color red ]
        [ ifelse (wealth <= (max-wealth * 2 / 3))
            [ set color green ]
            [ set color blue ] ] ]


to go
  ask turtles
    [ turn-towards-snow ]  ;; choose direction holding most snow within the turtle's vision and downhill
  ask turtles
    [ move-eat-soreness-die ]
  ;; grow snow every snow-fall-interval clock ticks
  if ticks mod snow-fall-interval = 0
    [ ask patches [ grow-snow ] ]
  ask turtles
    [ update-wealth-ability ] ;; tracks the wealth for each ability level

;; determine the direction which is most profitable for each turtle in
;; the surrounding patches within the turtles' vision
;; re-worked to make them only go across, diagonal, or straight down the hill

to turn-towards-snow  ;; turtle procedure
  set heading one-of (range 90 270)
  let best-direction 180
  let best-amount snow-ahead
  set heading 90
  if (snow-ahead > best-amount)
    [ set best-direction 90
      set best-amount snow-ahead ]
  set heading 135
  if (snow-ahead > best-amount)
    [ set best-direction 135
      set best-amount snow-ahead ]
  set heading 180
  if (snow-ahead > best-amount)
    [ set best-direction 180
      set best-amount snow-ahead ]
  set heading 225
  if (snow-ahead > best-amount)
    [ set best-direction 225
      set best-amount snow-ahead ]
  set heading 270
  if (snow-ahead > best-amount)
    [ set best-direction 270
      set best-amount snow-ahead ]
  set heading best-direction

to-report snow-ahead  ;; turtle procedure
  let total 0
  let how-far 1
  repeat vision
    [ set total total + [snow-here] of patch-ahead how-far
      set how-far how-far + 1 ]
  report total

to grow-snow  ;; patch procedure
  ;; if a patch does not have it's maximum amount of snow, add
  ;; num-snow-fall to its snow amount
  if (snow-here < max-snow-here)
    [ set snow-here snow-here + num-snow-fall
      ;; if the new amount of snow on a patch is over its maximum
      ;; capacity, set it to its maximum
      if (snow-here > max-snow-here)
        [ set snow-here max-snow-here ]
      recolor-patch ]

;; each turtle skis foward to the snow on its patch.  if there are multiple
;; turtles on a patch, divide the snow evenly among the turtles

to ski-forward
  ; have turtles ski the snow based on ability
  ask turtles
    [ set wealth floor (wealth + ((snow-here * ability ^ ability-advantage) / (count turtles-here))) ]
  ;; now that the snow has been skied, have the turtles make the
  ;; patches which they are on have less snow
  ask turtles
    ;; each skier removes some of the fresh snow
    ;; the amount removed increases based on ability and ability-advantage
    [ set snow-here (snow-here - (ability ^ ability-advantage) * 10)
      recolor-patch ]

to move-eat-soreness-die  ;; turtle procedure
  ;; each skier moves
  fd ability
  ;; skiers tire faster and faster over time
  set wealth (wealth - soreness)
  ;; grow more tired
  set soreness (soreness + 1)
  ;; check for "death" conditions: if you have no more wealth or
  ;; you're more tired than you have energy to continue,
  ;; then you "die" and are "reborn" (in fact, your variables
  ;; are just reset to new random values)
  if (wealth < 0) or (soreness >= energy)
    [ set-initial-turtle-vars ]

;; this procedure recomputes the value of gini-index-reserve
;; and the points in lorenz-points for the Lorenz and Gini-Index plots

to update-lorenz-and-gini
  let sorted-wealths sort [wealth] of turtles
  let total-wealth sum sorted-wealths
  let wealth-sum-so-far 0
  let index 0
  set gini-index-reserve 0
  set lorenz-points []

  ;; now actually plot the Lorenz curve -- along the way, we also
  ;; calculate the Gini index.
  ;; (see the Info tab for a description of the curve and measure)
  repeat num-skiers [
    set wealth-sum-so-far (wealth-sum-so-far + item index sorted-wealths)
    set lorenz-points lput ((wealth-sum-so-far / total-wealth) * 100) lorenz-points
    set index (index + 1)
    set gini-index-reserve
      gini-index-reserve +
      (index / num-skiers) -
      (wealth-sum-so-far / total-wealth)

to update-wealth-ability
  if (ability = 1)
    [set wealth-ability-1 (wealth-ability-1 + wealth)]
  if (ability = 2)
    [set wealth-ability-2 (wealth-ability-2 + wealth)]
  if (ability = 3)
    [set wealth-ability-3 (wealth-ability-3 + wealth)]

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

There is only one version of this model, created 2 months ago by Spencer Murphy.

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