Preferential Attachment, Homophily etc. Networks

turtles-own [wealth my-probability-of-homophily]
globals[number-homophily number-contagion flag]
extensions[nw]

to setup
  clear-all
  nw:set-context turtles links
  ask patches [set pcolor white]
  create-turtles number-of-nodes [
    set wealth Random 20
    set shape "circle"
    set color scale-color green wealth -5 25
    set size 1
    setxy random-xcor random-ycor
    set my-probability-of-homophily random probability-of-homophily]
  reset-ticks
end 

to go
  ask links [set color gray]
  ask one-of turtles [
  make-node-homophily find-partner wealth] ;
   if number-homophily >= number-of-links [ask links [set color gray] ask one-of turtles [set color red] stop]
  
  tick
  if layout? [layout]
end 

to contagion
  set flag 0
  if any? turtles with [color != red and count link-neighbors > 0]
  [
    ask turtles with [color = red]
    [
      ask link-neighbors [if random 100 <= probability-linked-affected [set color red set flag 1]
        ask other turtles [
        if random 100 < probability-other-affected [set color red set flag 1]]
      ]
    ]
    if flag = 1 [set number-contagion number-contagion + 1] 
  ]
end 

to make-node-homophily [node]
  if node != nobody
  [
        create-link-with node [set color red]
        move-to node
        fd 8
  ]
        set number-homophily number-homophily + 1
end 

to-report find-partner [W]
  ifelse random 100 < my-probability-of-homophily
 [report one-of other turtles with [wealth = W or wealth = W - 1 or wealth = W + 1]]
 [report one-of other turtles with [wealth > W]]
end 
;;;;;;;;;;;;;;
;;; Layout ;;;
;;;;;;;;;;;;;;

;; resize-nodes, change back and forth from size based on degree to a size of 1

to resize-nodes
  ifelse all? turtles [size <= 1]
  [
    ;; a node is a circle with diameter determined by
    ;; the SIZE variable; using SQRT makes the circle's
    ;; area proportional to its degree
    ask turtles [ set size sqrt sqrt count link-neighbors ]
  ]
  [
    ask turtles [ set size 1 ]
  ]
end 

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) (10 / factor) (10 / 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