Resonance Model

globals [
  a1 ; angle of planet 1 from positive horizontal
  a2 ; angle of planet 2 from positive horizontal
  p1 ; the period of the first planet
  p2 ; the period of the second planet
  r1 ; the radius of the first planet
  r2 ; the radius of the second planet
  period_1 ; to display period of first planet
  period_2 ; to display period of second planet
]

breed [stars star]
breed [planets planet]

to setup
  clear-all

  set r1 (r_1 * 100)
  set r2 (r_2 * 100)
  set-periods

  create-stars 1[
    set color yellow
    set size 3
    set shape "circle"
    setxy 0 0
  ]
  create-planets 2[
    set size 1
    set shape "circle"
  ]

  ask planet 1 [
    set color blue
    set heading 0
    fd r1
    rt 90
  ]
  ask planet 2 [
    set color red
    set heading 0
    fd r2
    rt 90
  ]

  reset-ticks

  output-print "The period of the first planet in days is:"
  output-print period_1
  output-print "The period of the second planet in days is:"
  output-print period_2
end 

to preset
  ask planet 1 [
    pen-down
    move-planet r1 p1
  ]

  ask planet 2 [
    pen-down
    move-planet r2 p2
  ]

  ifelse (a1 = a2) [
    ask planets [
      set color white
    ]
  ]
  [
    ask planet 1 [
      set color blue
    ]
    ask planet 2 [
      set color red
    ]
  ]

  set-slopes
  tick

  if ticks = 1500000 [
    stop
  ]
end 

to set-slopes
  ask planet 1 [
    ifelse (pxcor != 0) [
      set a1 atan pxcor pycor
    ]
    [
      ifelse (pycor > 0) [
        set a1 0
      ]
      [
        set a1 180
      ]
    ]
  ]

  ask planet 2 [
    ifelse (pxcor != 0) [
      set a2 atan pxcor pycor
    ]
    [
      ifelse (pycor > 0) [
        set a2 0
      ]
      [
        set a2 180
      ]
    ]
  ]
end 

to setup-free
  clear-all
  set r1 (radius-1 * 100)
  set r2 (radius-2 * 100)
  set p1 (period-1 / 100)
  set p2 (period-2 / 100)

  create-stars 1[
    set color yellow
    set size 3
    set shape "circle"
    setxy 0 0
  ]
  create-planets 2[
    set size 1
    set shape "circle"
  ]

  ask planet 1 [
    set color blue
    set heading 0
    fd r1
    rt 90
  ]
  ask planet 2 [
    set color red
    set heading 0
    fd r2
    rt 90
  ]

  reset-ticks
end 

to free-play

  ask planet 1 [
    pen-down
    move-planet r1 p1
  ]

  ask planet 2 [
    pen-down
    move-planet r2 p2
  ]

  ifelse (a1 = a2) [
    ask planets [
      set color white
    ]
  ]
  [
    ask planet 1 [
      set color blue
    ]
    ask planet 2 [
      set color red
    ]
  ]

  set-slopes

  tick

  if ticks = 1500000 [
    stop
  ]
end 

to move-planet [r p]
  fd (pi * r / 180) * (p / 50)
  rt p / 50
end 

to set-periods
  ; system 1
  if (r_1 = 0.0919) and (r_2 = 0.1087) [
    set period_1 10.340
    set period_2 13.286
    set p1 (period_1 / 100)
    set p2 (period_2 / 100)
  ]
  ; system 2
  if (r_1 = 0.1370) and (r_2 = 0.1720) [
    set period_1 18.357
    set period_2 25.648
    set p1 (18.357 / 100)
    set p2 (25.648 / 100)
  ]
  ; system 3
  if (r_1 = 0.0740) and (r_2 = 0.0890) [
    set period_1 7.008
    set period_2 8.719
    set p1 (7.008 / 100)
    set p2 (8.719 / 100)
  ]
  ; system 4
  if (r_1 = 0.0798) and (r_2 = 0.0649) [
    set period_1 8.689
    set period_2 19.535
    set p1 (8.689 / 100)
    set p2 (19.535 / 100)
  ]
  ; system 5
  if (r_1 = 0.1153) and (r_2 = 0.1283) [
    set period_1 13.868
    set period_2 16.219
    set p1 (13.868 / 100)
    set p2 (16.219 / 100)
  ]
  ; system 6
  if (r_1 = 0.0370) and (r_2 = 0.0590) [
    set period_1 7.384
    set period_2 14.789
    set p1 (7.384 / 100)
    set p2 (14.789 / 100)
  ]
end