Opinion Dynamics: Friedkin-Johnsen Model - Basic

globals [
  num-agents          ;; Number of agents
  neighbor-radius     ;; Radius for neighbor detection
  step-counter        ;; Time step counter
]

turtles-own [
  opinion             ;; Agent's opinion (0-1)
  self-weight         ;; Weight given to self-opinion
  neighbor-weights    ;; List associating neighbors with their weights
]

to setup
  clear-all
  reset-ticks

  ;; Parameter initialization
  set num-agents 200
  set neighbor-radius 5
  set step-counter 0

  ;; Create agents (uniform distribution)
  create-turtles num-agents [
    set shape "circle"
    set size 1.5

    ;; Random position and opinion
    setxy random-xcor random-ycor
    set opinion random-float 1  ;; Uniformly distributed initial opinions
    update-weights  ;; Initialize weights
    update-color    ;; Set color based on opinion
  ]
end 

to update-weights
  ;; Clear and recalculate all weights
  set self-weight 0.2  ;; Fixed self-weight at 0.2
  set neighbor-weights []  ;; Empty neighbor weights list

  ;; Get neighbor agents (excluding self)
  let my-neighbors other turtles in-radius neighbor-radius
  let neighbor-total-weight 0
  let neighbor-list sort my-neighbors

  ;; Calculate neighbor weights (excluding self)
  foreach neighbor-list [ n ->
    let dist distance n
    let w exp (-5 * dist)  ;; Weight calculated using exponential decay
    set neighbor-weights lput (list n w) neighbor-weights
    set neighbor-total-weight neighbor-total-weight + w
  ]

  ;; Normalize neighbor weights (sum of neighbor weights = 1)
  let normalized-neighbor-weights []
  foreach neighbor-weights [ pair ->
    let neighbor item 0 pair
    let weight item 1 pair
    set normalized-neighbor-weights lput (list neighbor (weight / neighbor-total-weight)) normalized-neighbor-weights
  ]

  set neighbor-weights normalized-neighbor-weights
end 

to update-color
  ;; More positive opinions (near 1) are lighter blue
  ;; More negative opinions (near 0) are darker blue
  set color scale-color blue opinion 0 1
end 

to go
  if not any? turtles [ stop ]

  ;; Update weights and calculate new opinions
  ask turtles [
    update-weights
    let new-op 0

    ;; Contribution from self-opinion
    set new-op new-op + self-weight * opinion

    ;; Weighted contributions from all neighbors
    let neighbor-influence 0
    foreach neighbor-weights [ pair ->
      let neighbor item 0 pair
      let weight item 1 pair
      set neighbor-influence neighbor-influence + weight * [opinion] of neighbor
    ]
    set new-op new-op + (1 - self-weight) * neighbor-influence

    set opinion new-op
    update-color  ;; Update color mapping
  ]

  set step-counter step-counter + 1
  tick
end