Online Community Simulator

globals [ total-membership-strength decay total-comments gini-index-membership lorenz-points gini-index-comms ]

turtles-own [my-comments]

breed [ members member ]
members-own [ extra-chattiness membership-strength join-date latest-interaction active?]

breed [ managers manager ]

directed-link-breed [ intimacy-links intimacy-link ]
intimacy-links-own [ strength ]

directed-link-breed [ interaction-links interaction-link ]
interaction-links-own [ comments latest ] ;; NetLogo does not support multiple edges! The "latest" property keeps
                                         ;; track of the last time member i communicated with members j

to setup
  ca
  reset-ticks
  set decay 1 / 100
  set-default-shape turtles "circle"
  ;; the initial network is a clique of numerosity founders + 1 manager
  create-managers 1 [ set color red  set my-comments 0]
  create-members founders [ set color white set join-date -1 set active? True set my-comments 0]
  ask members [ create-intimacy-links-to other members ]
  ask intimacy-links [ set strength 1 ]
  ask members [ set extra-chattiness 0 ]
  layout
  update-membership-strength
  update-lorenz-and-gini
  repeat count members [ tick ]
  reset-timer
end 

to go
  create-members 1 [
    set color white
    setxy random-xcor random-ycor
    set join-date ticks
    set active? True
    set my-comments 0
    ]
  converse
  update-intimacy-links
  update-membership-strength
  if count members > num-members [ show ( word "Time elapsed: " timer " seconds.") stop ]
  manage-community
  update-lorenz-and-gini
  update-gini-comms
  tick
end 

to converse
  ;; each member must decide whether to engage in interaction.
  ;; probability of engaging increases if member received communication the previous period.
  ask members with [ active? ] [
    if my-in-interaction-links with [ latest = ticks - 1 ] != nobody [ ;; need to distinguish between in-interaction-links of community managers and those of members. Need an agentset with two "with" conditions!
      set extra-chattiness 0.2
      ]
    if random-float 1.0 <= chattiness + extra-chattiness [
      connect
    ]
    set extra-chattiness 0 ;; after the decision to connect reset the extra chattiness
  ]
  ;; layout
end 

to connect
  ;; the member has decided to engage, now she must select the target of her communication.
  ;; average number of targets is 1
  ;; iterate over other members. Prob of creating an interaction-link with another member depends
  ;; on (relative) strength of intimacy-links with it
  ;; compute each numerator and decide whether to engage.
  let denominator count members ;; the denominator of equation (1) in the PDF file is at least count members
  let connect? False
  ask other members [
    let strength1 0
    let strength2 0
    if in-intimacy-link-from myself != nobody [
      ask in-intimacy-link-from myself [ set strength1 strength ]
      if out-intimacy-link-to myself != nobody [
        ask out-intimacy-link-to myself [ set strength2 strength ]
        set denominator denominator + 1 + intimacy-strength * strength1 * strength2
      ]
    ]
  ]
  ask other members [
    let numerator 1
    let strength1 0
    let strength2 0
    if in-intimacy-link-from myself != nobody [
      ask in-intimacy-link-from myself [ set strength1 strength ]
      if out-intimacy-link-to myself != nobody [
        ask out-intimacy-link-to myself [ set strength2 strength ]
        set numerator 1 + intimacy-strength * strength1 * strength2
      ]
    ]
    if numerator / denominator > random-float 1.0 [  ;; roll the dice for connecting each other member
      set connect? True  ;; keep track that at least one connection happened
      set my-comments my-comments + 1
      set total-comments total-comments + 1
      create-interaction-link-from myself [ set color 93 ] ;; if there already was one, the instruction is ignored
      ask in-interaction-link-from myself [
          set latest ticks
          set comments comments + 1
        ]
        create-intimacy-link-from myself ;; if there already was one, the instruction is ignored
        ask in-intimacy-link-from myself [ set strength strength + 1]
      ]
  ]
  if connect? = True [ set latest-interaction ticks ]
end 

to update-intimacy-links
  ask intimacy-links [
    set strength strength / ( 1 + decay )
  ]
end 

to update-membership-strength
  ask members with [ active? ] [
    let ms 0
    ask my-in-intimacy-links [
      set ms ms + strength
    ]
    set membership-strength ms
    if membership-strength < threshold and ticks - join-date > 50 [
      set active? False
      set color grey
      set membership-strength 0
      ]
    set total-membership-strength total-membership-strength + ms
  ]
end 

to manage-community
  if onboard = True [
    ask managers [ do-onboarding ]
  ]
  if engage = True [
    ask managers [ do-engagement ]
  ]
end 

to do-onboarding
  if ticks > 0 [
    create-interaction-links-to members with [ join-date = ticks - 1 ] [
      set latest ticks
      set comments 1
    ]
    create-intimacy-links-to members with [ join-date = ticks - 1  ] [
      set strength 1
    ]
    set my-comments my-comments + count members with [ join-date = ticks - 1 ] ;; in this model this is always 1.
  ]
end 

to do-engagement
  if ticks > 0 [ ;; to avoid generalized engagement in the first tick
    create-interaction-links-to members with [ latest-interaction = ticks - 1 ] [ set color 93 ] ;; if it's already there, it will be ignored
    create-intimacy-links-to members with [ latest-interaction = ticks - 1 ] ;; ditto
    let this-tick-comms 0
    ask members with [ latest-interaction = ticks - 1 ] [
      ask in-interaction-link-from myself [
        set latest ticks
        set comments comments + 1
        set this-tick-comms this-tick-comms + 1
      ]
      ask in-intimacy-link-from myself [ set strength strength + 1 ]
    ]
    set my-comments my-comments + this-tick-comms
  ]
end 

;; ============ REPORTERS ========================

;; COMPUTE LORENZ CURVE AND GINI COEFFICIENT
;; adapted from Wilensky, U. (1998). NetLogo Wealth Distribution model.
;; http://ccl.northwestern.edu/netlogo/models/WealthDistribution.
;; 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-ms sort [membership-strength] of members
  let total-ms sum sorted-ms
  let ms-sum-so-far 0
  let index 0
  set gini-index-membership 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 count members [
    set ms-sum-so-far (ms-sum-so-far + item index sorted-ms)
    set lorenz-points lput ((ms-sum-so-far / total-ms) * 100) lorenz-points ;; lput is like append in Python
    set index (index + 1)
    set gini-index-membership
    gini-index-membership +
    (index / count members ) -
    (ms-sum-so-far / total-ms )
  ]
end 

to-report dropouts
  report count members -  count members with [ active? ]
end 

to update-gini-comms ;
  let sorted-mc sort [my-comments] of members
  let total-mc sum sorted-mc
  let mc-sum-so-far 0
  let index-comms 0
  set gini-index-comms 0

  ;; calculate the Gini index.
  repeat count members [
    set mc-sum-so-far (mc-sum-so-far + item index-comms sorted-mc)
    set index-comms (index-comms + 1)
    set gini-index-comms
    gini-index-comms +
    (index-comms /  count members ) -
    (mc-sum-so-far / (total-mc + 0.000001 ))
  ]
end 


;; =============================================================
;; LAYOUT PROCEDURE
;; stolen from the preferential attachment model by Uri Wilensky

to layout
  ;; the number 3 here is arbitrary; more repetitions slows down the
  ;; model, but too few gives poor layouts
  repeat 3 [
    ;; the more turtles we have to fit into the same amount of space,
    ;; the smaller the inputs to layout-spring we'll need to use
    let factor sqrt count turtles
    ;; numbers here are arbitrarily chosen for pleasing appearance
    layout-spring turtles links (1 / factor) (15 / factor) (4 / factor)
    display  ;; for smooth animation
  ]
  ;; don't bump the edges of the world
  let x-offset max [xcor] of turtles + min [xcor] of turtles
  let y-offset max [ycor] of turtles + min [ycor] of turtles
  ;; big jumps look funny, so only adjust a little each time
  set x-offset limit-magnitude x-offset 0.1
  set y-offset limit-magnitude y-offset 0.1
  ask turtles [ setxy (xcor - x-offset / 2) (ycor - y-offset / 2) ]
end 

to-report limit-magnitude [number limit]
  if number > limit [ report limit ]
  if number < (- limit) [ report (- limit) ]
  report number
end 

to-report manager-comms
  report [my-comments] of turtle 0
end 
;; =================================================