MIHS - CoronaVirus2.0

turtles-own
  [ sick?                ;; if true, the turtle is infectious
    remaining-immunity   ;; how many weeks of immunity the turtle has left
    sick-time            ;; how long, in weeks, the turtle has been infectious
    age ]                ;; how many weeks old the turtle is

globals
  [ %infected            ;; what % of the population is infectious
    %immune              ;; what % of the population is immune
    days                 ;; cumulative number of days in simulation
    deaths               ;; cumulative number of deaths due to virus
    lifespan             ;; the lifespan of a turtle - the chance of dying when infected is higher for older turtles
    immunity-duration    ;; how many weeks immunity lasts
    cumulative-age       ;; used to calculate average age of population
    ticks-per-week ]     ;; # of ticks to simulate 1 week of time


;; The setup is divided into four procedures

to setup
  clear-all
  setup-constants
  setup-turtles
  update-global-variables
  update-display
  reset-ticks
end 

;; We create a variable number of turtles of which 10 are infectious,
;; and distribute them randomly

to setup-turtles
  create-turtles number-people
    [ setxy random-xcor random-ycor
      set age ( random average-age + random lifespan * .75 )  ;; age is randomly distributed around the average value
      if age > lifespan + 30 [ set age lifespan + random 30 ]
      set cumulative-age cumulative-age + age
      set sick-time 0
      set remaining-immunity 0
      set size 1.5  ;; easier to see
      ;; set label age
      get-healthy ]
  ;; calculate average age
  set cumulative-age cumulative-age / number-people
  ask n-of 10 turtles
    [ get-sick ]
end 

to get-sick ;; turtle procedure
  set sick? true
  set remaining-immunity 0
end 

to get-healthy ;; turtle procedure
  set sick? false
  set remaining-immunity 0
  set sick-time 0
end 

to become-immune ;; turtle procedure
  set sick? false
  set sick-time 0
  set remaining-immunity immunity-duration
end 

;; This sets up basic constants of the model.

to setup-constants
  set lifespan 80     ;; average lifespan is assumed to be 80 years - the chance of dying when infected is higher for older turtles
  set immunity-duration 52
  set ticks-per-week 70
end 

to go
  ask turtles [
    update-sick-immune
    move
    if sick? [ recover-or-die ]
    if sick? [ infect ]
  ]
  update-global-variables
  update-display
  tick
end 

to update-global-variables
  if count turtles > 0
    [ set %infected (count turtles with [ sick? ] / count turtles) * 100
      set %immune (count turtles with [ immune? ] / count turtles) * 100 ]
end 

to update-display
  ask turtles
    [ if shape != turtle-shape [ set shape turtle-shape ]
      set color ifelse-value sick? [ red ] [ ifelse-value immune? [ green ] [ grey ] ] ]
end 

;; turtle counting variables are advanced either daily or once per week (i.e. only after ticks-per-week ticks have passed)

to update-sick-immune ;; turtle procedure
  ;; check that 1 day has passed and update sick-time
  if ticks mod ( ticks-per-week / 7 ) = 0 [
    if sick? [ set sick-time sick-time + 1 ]
  ]
  ;; check that 1 week has passed and update remaining-immunity
  if ticks mod ticks-per-week = 0 [
    if immune? [ set remaining-immunity remaining-immunity - 1 ]
  ]
end 

;; turtles move about at random.

to move ;; turtle procedure
  right random 100
  left random 100
  forward 1
end 

;; If a turtle is sick, it infects other turtles on the same patch.
;; Immune turtles don't get sick.

to infect ;; turtle procedure
  ask other turtles-here with [ not sick? and not immune? ]
    [ if random-float 100 < infectiousness
      [ get-sick ] ]
end 

;; Once the turtle has been sick long enough, it
;; either recovers (and becomes immune) or it dies.

to recover-or-die ;; turtle procedure
  if sick-time > duration                        ;; If the turtle has survived past the virus' duration, then
    [ ifelse ( random-float 150 * age / lifespan ) < chance-recover   ;; either recover or die - older turtles have a lower chance of recovery
      [ become-immune ]
      [ set deaths deaths + 1  die ]
    ]
end 

to-report immune?
  report remaining-immunity > 0
end 

to startup
  setup-constants ;;
end 


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