Safe Sex Attitudes and Behaviors

;;; --------------------------------------------------------------------- ;;;
;; --- Temporary breeds for setting up social groups/cliques --- ;;

;; default turtle type, will later be changed to male or female
breed [ people person ]
breed [ leaders leader ] ;; "clique leader" in a way
                         ;; helps with creating spatial layout and
                         ;; (optional) some initial links between groups

;; Breeds (agentsets) for gender
;; (once social groups/networks established)
breed [males male]
breed [females female]

;; a way to access the links to members of each clique
links-own [ group ]

;; Link breeds - turtles can either be friends, or sexual partners
; In this model, turtles can have multiple friends,
; but only one sexual partner at a time
undirected-link-breed [sexual-partners sexual-partner]
undirected-link-breed [friends friend]


;;; --------------------------------------------------------------------- ;;;
;;;
;;; GLOBAL VARIABLES
;;;
;;; --------------------------------------------------------------------- ;;;

globals
[
  ;; The next 3 values are set by sliders, where default is scale 0 - 100
  
  ;; The chance out of 100 that an infected person will transmit infection
  ;; during one week of couplehood if they have unsafe sex
  ;infection-chance 
  
  ;; Used as an average for generating chance out of 100 that an agent 
  ;; will use/wants to use a condom (depends on gender)
  ;avg-female-condom-intention 
  ;avg-male-condom-intention  
                             
  
  ;; The next two values are used only in assign-sex-ed-level, and
  ;; will be assigned depending on the %-receive-condom-sex-ed slider value
  ;; Average level of accurate knowledge if agent received:
  no-condom-sex-ed-level ;; sex education that did not include/cover condom use
  condom-sex-ed-level    ;; sex education that included condom use for STI protection
  
  
  ;; The next two values are determined by the symptomatic? chooser
  males-symptomatic?   ;; If true, males will be symptomatic IF infected with an STI
  females-symptomatic? ;; If true, females will be symptomatic IF infected with an STI
                                 

  ;; The next two values are the maximum value for tendency of any agent 
  ;; to make a friend or sexual partner link on a given turn. (scale 1 to 100)
  ;; Used as an upper bound for generating random chance for individual agents 
  max-friendship-factor ;; Maximum friendship-making-coupling tendency value
  max-coupling-factor   ;; Maximum coupling tendency value (sexual partner)
                     
  ;; The next two values are the average tendency of an agent to form a
  ;; friendship/sexual partnership with another agent
  ;; Both are set to the max factor / 2
  ;; Average tendency of a person to couple with another person
 
  avg-friendship-tendency ;; Average tendency of a person to make friends with another person
  avg-coupling-tendency   ;; Average tendency of a person to couple with another person 
                          ;; in order to couple, the pairings must consist of one male and one female,
                          ;; and both partners must be single/uncoupled

  avg-relationship-length ;; Average number of ticks a sexual partnership/couple will stay together (commitment)
  
  
  certainty-delta ;; the amount that certainty increases
                  ;; whenever an agent repeats their attitude to others
                  ;; as certainty increases, it becomes harder to change an agent's opinion
  
  justification-delta ;; the amount that justification decreases
                      ;; every time an agent thinks they "got away" with unsafe sex
 
]


;;; --------------------------------------------------------------------- ;;;
;;;
;;; Turtle/Agent Variables
;;;
;;; --------------------------------------------------------------------- ;;;

turtles-own
[
  ;; The percent chance a person uses protection (condoms) while in a couple
  ;; The likelihood (0 - 100%) of this agent practicing safe sex (reflects behavior)
  ;; Likelihood is influenced by three components:
  ;; attitude, certainty, and justification

  safe-sex-likelihood

  ;; Variable used to determine how much this agent's safe sex likelihood
  ;; has changed since the last tick
  old-safe-sex-likelihood 
  
  ;; ATTITUDE:
  ;; The intention or desire of an agent to practice safe sex (use a condom)
  ;; Evolves over time through talking to peers, or becoming infected
  attitude 
                 
  
  ;; CERTAINTY:
  ;; how confidently/strongly an agent feels about their attitude
  ;; The chance that an attitude changes is inversely proportional to certainty
  certainty ;; initially set to mesosystem-condom-encouragement
            ;; i.e. how much their upbringing encouraged safe sex
            ;; might consist of parents' beliefs, life experiences, religious attitudes, etc.
  
  
  ;; JUSTIFICATION:
  ;; the logic or reasoning to rationalize having a postive attitude towards safe sex,
  ;; which is independent of how strongly they feel about it (certainty)
  ;; or what their actual attitude is
  justification ;; initially set to the level of accurate education this agent has about safe sex and condom usage
  
  
  had-unsafe-sex? ;; Whether this person had sex without a condom on the last tick
  
  infected? ;; If true, the person is infected (and infectious)
  known?    ;; The person is infected and knows it (due to being symptomatic)
  ;; In this model, agents that know they are infected
  ;; always use condoms to protect their sexual partners
  ;; If an agent is not symptomatic/of a symptomatic gender,
  ;; their known? variable never gets set to true, which 
  ;; may enable an STI to more easily spread through a population
  
  coupled?      ;; If true, the person is in a sexually active couple.
  partner       ;; The person that is our current partner in a couple.
  couple-length ;; How long the person has been in a couple.
  
  friendship-tendency ;; How likely this person is to make a new friend
  coupling-tendency   ;; How likely the person is to join a couple.
  commitment          ;; How long the person will stay in a couple/relationship.
  
  group-membership ;; which clique/friend group/cluster this agent is part of
  
  num-friends ;; The number of friends that an agent wants to have

]


;;; --------------------------------------------------------------------- ;;;
;;;
;;; SETUP PROCEDURES
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Calls all separate setup functions - setting globals, cliques, individuals
;;
;;

to setup
  clear-all
  setup-globals
  setup-clusters ;; set up social groups/cliques
  setup-people   ;; change breeds to male/female, set individual turtle attributes
  
  ;; By default, setup infects two random individuals in the model with an STI
  ;; but if you want to also explore spread of attitudes without an STI spreading
  ;; through the population, comment out the line below

  infect-random ;; infect one random male and one random female

               
  ; To set up, don't initialize any sexual partnerships, since
  ; they'll form on their own (i.e. only create friendship links) 
  ask links [assign-link-color]
  
  reset-ticks
end 

;;; --------------------------------------------------------------------- ;;;
;;
;; Initialize global variables
;;

to setup-globals
  
  ;; the amount certainty increases when an agent repeats their attitude
  set certainty-delta .1 
  
  ;; the amount justification decreases when an agent thinks they "got away with" unsafe sex
  set justification-delta 2
  
  ;; These could also be set in assign-sex-ed-level
  set no-condom-sex-ed-level 20
  set condom-sex-ed-level 80
  
  ;; Call functions to set whether females and males show symptoms of the STI
  ;; based on value of chooser/drop-down in interface
  run word "set-" symptomatic?
  
  ;; For simplicity, use predetermined values to set these variables
  ;; (compared to AIDS model, which uses sliders) 
  
  set max-friendship-factor 70
  set max-coupling-factor 40
  set avg-friendship-tendency (max-friendship-factor / 2)
  set avg-coupling-tendency (max-coupling-factor / 2)
  set avg-relationship-length 25
end 


;;
;; Setter functions for the symptomatic? chooser/drop-down
;;
;;

to set-females-symptomatic?
  set females-symptomatic? true
  set males-symptomatic? false
end 

to set-males-symptomatic?
  set males-symptomatic? true
  set females-symptomatic? false
end 

to set-both-symptomatic?
  set females-symptomatic? true
  set males-symptomatic? true
end 

to set-neither-symptomatic?
  set males-symptomatic? false
  set females-symptomatic? false
end 



;;; --------------------------------------------------------------------- ;;;
;;
;; Set up social clusters of networked agents
;;
;;

to setup-clusters
  
  create-leaders num-cliques [ ]
  
  ;; The number of total inter-group links between members
  let num-links ( ( avg-num-friends - 1 ) * clique-size ) / 2
  ; The - 1 accounts for each member initially linking to the leader
  ; Multiplying by clique-size ensures there are enough for all group members
  ; Then divide by 2, since you only need 1 link to connect 2 people
  
  ;; if only 1 cluster, leader setxy 0 0 by default
  if (num-cliques > 1) ;; if more than 1 cluster
  [
    ;; The "leaders" are the central person of the clique/social group
    layout-circle leaders 10

    ;; Create links between all "leaders"
    ask leaders [ create-friends-with other leaders ]
    ; Assume that all leaders interact/are social butterflies/charismatic,
    ; hence why their entire friend group likes them too.
  ]
  
  let groupID 0
  while [ groupID < num-cliques ]
  [
    create-people clique-size [ set group-membership groupID ]
    
    ;; if only 1 cluster, layout-circle works 14.5
    ;; leader is in the center of the group
    layout-circle people with [group-membership = groupID ] 5 - 0.5 * max( list (num-cliques - 5) (0) )
    ask people with [group-membership = groupID ]
    [
      setxy xcor + [xcor] of leader groupID ycor + [ycor] of leader groupID
      create-friend-with leader groupID
    ]
    
    ;; Agents make friendship links with people in their clique/friend circle
    let linkcounts 0
    while [linkcounts < num-links ]
    [
      ask one-of people with [group-membership = groupID]
      [
        let choice (one-of other people with [not link-neighbor? myself and group-membership = groupID])
        if choice != nobody
          [
            create-friend-with choice [ set group groupID ]
            set linkcounts linkcounts + 1
          ]
      ]
    ]
    
    ;; Increment the groupID to differentiate clique ID #'s
    set groupID groupID + 1
  ]
  
  ;; Leaders are used for spatially setting up discrete clusters
  ;; and for providing some links between groups.
  ;; If they are disabled, there are no initial inter-group links,
  ;; but agents might still form friendships or sexual partnerships 
  ;; with agents that are not in their clique.
  if (not social-butterflies?) [ask leaders [ die ] ]
end 


;;; --------------------------------------------------------------------- ;;;
;;
;; Initialize individual agents by setting gender and unique member variables
;;
;;

to setup-people
  
  ;; Don't actually CREATE turtles here, that's done by setup-clusters
  ask turtles
  [
    ;; Set ideal number of friends for each agent to
    ;; the initial number of friend links they have
    set num-friends (count friend-neighbors)
    
    set breed males ;; Default breed male, change half to female later
    set coupled? false ;; Everyone is initially single
    set partner nobody
    set had-unsafe-sex? false ;; Whether this person had unsafe sex on the last tick
    
    set infected? false ;; Initially, no one is infected
    set known? false
                                       
  ]
  
  ;; Set genders of turtles to be 50% male, 50% female
  ask n-of (count turtles / 2) turtles [set breed females ]
  
  ask turtles
  [
    ;; Individual variables per agent are set randomly following
    ;; a normal distribution based on slider or global values
    assign-normally-distributed-member-variables
    
    
    ;; Determine how much this agent's likelihood of practicing safe sex
    ;; has changed since last tick.
    ;; (If likelihoods of all agents stop changing significantly,
    ;; the simulation will stop.)
    update-safe-sex-likelihood
    set old-safe-sex-likelihood safe-sex-likelihood
    
    
    assign-turtle-color ;; Color is determined by likelihood of practicing safe sex
    assign-shape        ;; Shape is determined by gender and sick status
    set size 2.5        ;; Make shapes a bit easier to distinguish by increasing size
  ]
end 


;;; --------------------------------------------------------------------- ;;;
;;
;; Helper procedure to approximate a "normal" distribution
;; around the given average value

;; Generate many small random numbers and add them together.
;; This produces a normal distribution of tendency values.
;; A random number between 0 and 100 is as likely to be 1 as it is to be 99.
;; However, the sum of 20 numbers between 0 and 5
;; is much more likely to be 50 than it is to be 99.
;; (from the AIDS model)

to-report random-near [center] ;; turtle procedure
  let result 0
  repeat 40 [ set result (result + random-float center) ]
  report result / 20
end 


;;
;; Assign values to variables of agents in the population using
;; the helper procedure RANDOM-NEAR so that individual agents variables
;; follow an approximately "normal" distribution around average values.
;;

to assign-normally-distributed-member-variables ;; turtle procedure
  
    ;;
    ;; The below variables will vary for each turtle, and the values
    ;; follow an approximately normal distribution
    ;;
    
    ;; How long the person will stay in a couple-relationship. (doesn't change)
    set commitment random-near avg-relationship-length
    
    ;; How likely the person is to join a couple. (doesn't change)
    set coupling-tendency random-near avg-coupling-tendency
    
    ;; How likely the person is to make a friend. (doesn't change)
    set friendship-tendency random-near avg-friendship-tendency
    
    
    ;; Note: Gender must be set before this is called!
    ;; Assign initial attitude towards safe sex based on gender
    ;; Attitude can change during the simulation through talking to peers
    ;; and being aware of contracting an STI
    ifelse (is-female? self)
    [ set attitude random-near avg-female-condom-intention ]
    [ set attitude random-near avg-male-condom-intention ]
    
    ;; Assign initial certainty based on mesosystem encouragement
    ;; Certainty increases whenever an agent repeats their attitude to others
    ;; Currently, certainty does not decrease in this model
    set certainty random-near avg-mesosystem-condom-encouragement
    
    ;; Assign initial justification based on sex ed agent received
    ;; Justification can decrease if agent thinks they "got away with" having unsafe sex
    ;; or increase if they contract an STI themselves
    ;; Note: in this model, the justification is not justification for
    ;; the attitude itself, but rather a justification for having safe sex
    assign-sex-ed-level
end 

;;
;; Assign a level of accurate knowledge of safe sex
;; normally distributed around a high or low value
;; based on type of sex ed the agent received.
;; Used to initialize the agent's justification.
;;

to assign-sex-ed-level ;; turtle procedure
  
  ;; Note: The condom-sex-ed level and no-condom-sex-ed-level are
  ;; static global values in this model for convenience. Since
  ;; they are only used here, they could be set locally instead.
  
  ifelse (random 100 <= %-receive-condom-sex-ed)
  [
    ;; If agent received sex ed including condom usage,
    ;; assume knowledge randomly distributed around HIGH value
    ;; (static global value)
    set justification random-near condom-sex-ed-level
  ]
  [
    ;; If agent received sex ed without condom usage,
    ;; Assume knowledge randomly distributed around LOW value
    set justification random-near no-condom-sex-ed-level
  ]
end 


;;; --------------------------------------------------------------------- ;;;
;;;
;;; Set color/shape of agents/links
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Set shape based on gender (male or female)
;; and whether or not infected (includes a dot)
;;

to assign-shape ;; turtle procedure
  ifelse infected?
  [
    ifelse is-male? self
    [
      ifelse known?
      [ set shape "male sick" ]
      [ set shape "male sick unknown" ]
    ]
    [
      ifelse known?
      [ set shape "female sick" ]
      [ set shape "female sick unknown" ]
    ]
  ]
  ;; otherwise, the turtle is not infected
  [
    ifelse is-male? self
    [set shape "male"]
    [set shape "female"]
  ]
end 


;;
;; Color of the agent reflects their individual 
;; likelihood of practicing safe sex
;;

to assign-turtle-color ;; turtle procedure
  
  ;; call this just in case a variable went out of accepted range
  cap-member-variables 
 
  ;06C106 green - 100% likely to engage in safe sex (using a condom)
  ;FFFFFF white - 50% likely of having safe sex 
  ;C10606   red  - 0% likely to use a condom (100% likely to have unsafe sex)
 
  ;; If there was a switch statement for NetLogo,
  ;; this would be where you'd use it
  if (safe-sex-likelihood >= 0) [ set color [ 193   6   6 ] ] ;; 0-5 % - red
  if (safe-sex-likelihood > 5)  [ set color [ 198  26  26 ] ] ;; 5-10 %
  if (safe-sex-likelihood > 10) [ set color [ 204  51  51 ] ] ;; 10-15 %
  if (safe-sex-likelihood > 15) [ set color [ 210  77  77 ] ] ;; 15-20 %
  if (safe-sex-likelihood > 20) [ set color [ 217 102 102 ] ] ;; 20-25 %
  if (safe-sex-likelihood > 25) [ set color [ 223 127 127 ] ] ;; 25-30 %
  if (safe-sex-likelihood > 30) [ set color [ 229 153 153 ] ] ;; 30-35 %
  if (safe-sex-likelihood > 35) [ set color [ 236 178 178 ] ] ;; 35-40 %
  if (safe-sex-likelihood > 40) [ set color [ 242 204 204 ] ] ;; 40-45 %
  if (safe-sex-likelihood > 45) [ set color [ 248 229 229 ] ] ;; 45-50 %
  if (safe-sex-likelihood = 50) [ set color [ 255 255 255 ] ] ;; 50% - white
  if (safe-sex-likelihood > 50) [ set color [ 229 248 229 ] ] ;; 50-55 %
  if (safe-sex-likelihood > 55) [ set color [ 204 242 204 ] ] ;; 55-60 %
  if (safe-sex-likelihood > 60) [ set color [ 178 236 178 ] ] ;; 60-65 %
  if (safe-sex-likelihood > 65) [ set color [ 153 229 153 ] ] ;; 65-70 %
  if (safe-sex-likelihood > 70) [ set color [ 127 223 127 ] ] ;; 70-75 %
  if (safe-sex-likelihood > 75) [ set color [ 102 217 102 ] ] ;; 75-80 %
  if (safe-sex-likelihood > 80) [ set color [  77 210  77 ] ] ;; 80-85 %
  if (safe-sex-likelihood > 85) [ set color [  51 204  51 ] ] ;; 85-90 %
  if (safe-sex-likelihood > 90) [ set color [  26 198  26 ] ] ;; 90-95 %
  if (safe-sex-likelihood > 95) [ set color [   6 193   6 ] ] ;; 95-100 % - green
  
  
  ;; The label is just redundant information of the color
  ;; but it is more precise (displays actual value)
  ;; since assign-turtle-color is updated on every tick
  ;; this can be called from within this function
  ifelse (show-labels?)
  [ set label (round safe-sex-likelihood) ]
  [ set label "" ]
end 


;;
;; Color of link indicates type of relationship between the two agents
;; blue is a friendship, magenta is a sexual partnership
;;

to assign-link-color ;; link procedure
  
  ifelse is-friend? self
    [ set color blue]
    [ set color magenta]
    
  set thickness .16 ; make the link a bit easier to see
end 



;;; --------------------------------------------------------------------- ;;;
;;;
;;; GO/RUNTIME PROCEDURES
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Run the simulation
;;

to go
  
  ;;; ----- Check for STOP conditions ----- ;;
  
  ;; Stop if every single turtle is infected
  if all? turtles [infected?] [ stop ]
  
  ;; If all agents reach a polarized safe-sex-likelihood,
  ;; or all agents are certain of their attitude (will not change any more)
  ;; the model has reached a stable state, so stop
  if all? turtles [
    safe-sex-likelihood < 0.1 or
    safe-sex-likelihood > 99.9 or
    certainty > 99.9
    ] [stop]
 
 
  ;; record each agent's likelihood before interacting with others,
  ;; and potentially getting/realizing they are infected 
  ask turtles [ set old-safe-sex-likelihood safe-sex-likelihood ]
  
  ask turtles
  [
    ;; Agents talk to their friends and sexual partner (if any), which
    ;; might impact his/her personal likelihood of practicing safe sex
    talk-to-peers
    
    ;; If already coupled with a sexual partner,
    ;; just increase length of relationship
    ;; (agents are monogamous in this simulation)
    ifelse coupled? [ set couple-length couple-length + 1 ]
    
    ;; If they are NOT coupled, agent tries to find a mate
 
    ;; Any agent can initiate mating if they are not coupled
    ;; (and random chance permits)
    [ if (random-float max-coupling-factor < coupling-tendency) [ couple ] ]
  ]
  
  ;; give everyone (coupled or not) a chance to make a friend
  ask turtles
  [
    ;; Everyone should attempt to make friends because otherwise,
    ;; the sexual partner links break and agents end up 
    ;; only being friends with agents of the same sex
    
    ;; If this agent has not reached their maximum limit of friends,
    ;; try to make a friend / create a friend link
    if ( (count friend-neighbors < num-friends) and
         random-float max-friendship-factor < friendship-tendency )
    [ make-friends ]
    
    ;; If this agent already has reached their maximum limit of friends,
    ;; don't try to create any more friend links
  ]
  
  ;; Agents will uncouple if the length of the relationship reaches
  ;; the commitment threshold for one of the partners
  ;; Call uncouple after make-friends and couple, 
  ;; because you wouldn't want exes immediately friending each other again,
  ;; and this model doesn't simulate instant rebounds
  ask turtles [ uncouple ]
  
  ;; If turtles are coupled (have a sexual partner), 
  ;; they will have sex on each tick, and have the potential
  ;; of spreading an STI if they have unprotected sex.
  ask turtles [ have-sex ]
  
  ;; In order to best simulate that STIs may not present symptoms immediately,
  ;; don't check if infected (known determined by being symptomatic)
  ;; until after talking to friends about attitude and having sex
  ask turtles [ check-infected ]
  
  ask turtles
  [ 
    update-safe-sex-likelihood
    assign-turtle-color ;; based on safe-sex-likelihood
  ]

  tick
end 


;;; --------------------------------------------------------------------- ;;;
;;
;; Update the likelihood (out of 100) that an agent
;; will practice safe sex (use a condom).
;;

to update-safe-sex-likelihood
  
  ;; The likelihood of an agent engaging in safe sex behaviors (using a condom)
  ;; is determined by a combination of the agent's:
  ;;   - attitude (desire)
  ;;   - justification (knowledgeable background/logical reasoning for safe sex attitude)
  
  ;; Certainty is assumed to be independent of attitude value itself,
  ;; even when the attitude is polarized (close to 100 or close to 0)
  ;; Certainty impacts how resistant an agent is to change their attitude
  ;; when talking to others, and how many others the agent interacts with,
  ;; but doesn't directly impact likelihood calculation.

  ;; cap variables just in case
  cap-member-variables ; make sure no variables got set to < 0 or > 100
  
  ;; Likelihood is strongly weighted by attitude
  let attitude-weight .75
  let justification-weight .25
  
  set safe-sex-likelihood (attitude * attitude-weight + justification * justification-weight)
end 


;;
;; Make sure the member variables don't exceed 100
;;

to cap-member-variables ;; turtle procedure
  if (safe-sex-likelihood > 100) [set safe-sex-likelihood 100]
  if (safe-sex-likelihood < 0) [set safe-sex-likelihood 0]
  if (attitude > 100) [set attitude 100]
  if (attitude < 0) [set attitude 0]
  if (certainty > 100) [set certainty 100]
  if (certainty < 0) [set certainty 0]
  if (justification > 100) [set justification 100]
  if (justification < 0) [set justification 0]
end   


;;; --------------------------------------------------------------------- ;;;
;;;
;;; SPREAD ATTITUDES
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Agent interacts with its friends (and sexual partner, if any)
;; and potentially alters its personal likelihood of practicing safe sex
;;

to talk-to-peers ;; turtle procedure
  
  ;; Use certainty to determine how many links this agent talks to per tick
  ;; The more certain a person is in their attitude,
  ;; the more likely they are to discuss it with their peers/links.
  
  let convoCount 0
  
  ;; NOTE: These "conversations"/"interactions" are one-directional in this model.
  ;; Additionally, an agent is not guaranteed to talk to their sexual partner
  while [ convoCount < ( certainty / 100 ) * ( count my-links ) ] 
  [
      
      let peer one-of link-neighbors ;; friends or sexual partner, if any
      if (peer != nobody)
      [
        ;; An agent grows more certain of their attitude
        ;; (regardless of what that attitude actually is)
        ;; every time they express it to someone else (repeated expression)
          
        set certainty certainty + certainty-delta
        
        
        ;; A person's certainty impacts how likely they are to change their attitude.
        ;; An agent with higher certainty is more resistant to changing their attitude.
        ;; (100 - certainty) is how likely an agent is to adjust their attitude.
        
        let attitude-change-chance ( (100 - certainty) / 100 )
        

        ;; However, an agent doesn't care about how confident their peer
        ;; feels about his/her attitude (their certainty), s/he only cares about
        ;; what reasoning they have to back up their attitude (justification).
        ;; So if the peer has strong justification of their attitude, 
        ;; the agent is more likely to be swayed
        
        let peer-persuasion-chance ( [justification] of peer / 100 )
        
        
        ;; Constants for dampening and getting desired reactions
        ;; calculated through tinkering with Excel formulas
        let scale-factor 10 
        let c 0.5
        
          
        ;; In order to account for polarity/extremity of attitude
        ;; subtract 50 from it to aid in the calculations
        ;; So "your" (this agent's) attitude scaled down to be between
            ;; -50 (very anti safe sex)
            ;; to 0 (neutral)
            ;; to 50 (very pro safe sex)   
            
        let my-attitude-scaled ( (attitude - 50) / scale-factor )
        let peer-attitude-scaled ( ([attitude] of peer - 50) / scale-factor )
        let temp-var ( my-attitude-scaled * my-attitude-scaled * peer-attitude-scaled / (scale-factor ^ 3) ) 
        
        let attitude-change ( c * attitude-change-chance * peer-persuasion-chance * temp-var)
        
        set attitude attitude + attitude-change
      ]
      
      set convoCount convoCount + 1
  ]
  
    ;; update personal likelihood based on talking to peers
    update-safe-sex-likelihood 
end 


;;; --------------------------------------------------------------------- ;;;
;;;
;;; SPREAD STI (potentially) / HAVE SEX
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Only agents with sexual partners (coupled) can spread an STI
;;
;;

to have-sex ;; turtle procedure (only for coupled turtles)
  
  
  ask turtles with [coupled?]
  [
    ;; Infection can occur if either person is infected, but the infection is unknown.
    ;; This model assumes that people with known infections will continue to couple,
    ;; but will always practice safe sex.

    ;; This model simulates sexual relations between a male and a female,
    ;; so I decided that only one of the partner's desire to use a condom
    ;; must be strong enough to make sure the couple has safe sex.
    
    ;; Extensions/modifications may choose to change this so that
    ;; for condom use to occur, BOTH people must want to use one.
    ;; This can be done by changing the primitive after the
    ;; second grouped condition of the ifelse statement from AND to OR

    ifelse ( (not known? and [not known?] of partner) and
             (random-float 100 > safe-sex-likelihood) AND   ;; Optional: change this to or for both people to have to want to use a condom
             (random-float 100 > ([safe-sex-likelihood] of partner))
           ) 
    [
      ;; If got past the above conditional, that means the couple had unprotected sex
      set had-unsafe-sex? true
      ask partner [ set had-unsafe-sex? true ]
      
      ;; They had unprotected sex, so infection is possible...
      if (random-float 100 < infection-chance)
      [
        ;; Spread virus between an infected and non-infected coupled partner duo
        if (infected?) [ ask partner [ become-infected ] ]
        if ([infected?] of partner) [ become-infected ]
      ]
    ]
    [
      set had-unsafe-sex? false
      ask partner [set had-unsafe-sex? false]
      
      ;; This model assumes that safe sex (using a condom) is always 
      ;; 100% effective in preventing the spread of infection - 
      ;; thus there is no random chance of the infection spreading if a condom is used.
      ;; This could be modified in extensions to be more realistic and
      ;; account for factors like incorrect/inconsistent condom usage,
      ;; condom failure, or STIs passed through other means.
    ]
  ]
end 


;;; --------------------------------------------------------------------- ;;;
;;;
;;; MAKE FRIENDS (Potential attitude influencers)
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Try to make friend links with other turtles
;; (will only be called if the turtle has not reached their maximum friend limit)
;; Uses similar approach as coupling, but gender doesn't matter
;;

to make-friends ;; turtle procedure
  
  ;; This agent's clique (social/friend group) id
  let groupID group-membership
  
  ;; Probability that friendship link will form
  ;; (arbitrary number to overwrite)
  let friending-probability 1.0
  
  ;; Probability of successful coupling decreases if the
  ;; potential friend is not part of the agent's clique
  ;; Note: these are arbitrary numbers that could be adjusted for more realistic modeling
  let in-group-probability 0.8
  let out-group-probability 0.2
  
  ;; No need to check for gender compatibility,
  ;; everyone can be friends with each other, yay!
  ;; However, the potential-friend must not have maxed out their friend count
  
  ;; A valid potential friend must not have reached his/her friend limit
  ;; (but gender is irrelevant).
  
  ;; First, try to find someone in their clique who is not a current link
  let potential-friend ( one-of other turtles with [not link-neighbor? myself
               and group-membership = groupID
               and (count friend-neighbors < num-friends)] )
  ifelse (potential-friend != nobody)
  [
    set friending-probability in-group-probability
  ]
  ;; If they couldn't find a potential friend within their friend group,
  ;; try finding the closest nearby agent
  [
    set potential-friend ( min-one-of (other turtles with [not link-neighbor? myself
                 and (count friend-neighbors < num-friends)]) [distance myself])
    set friending-probability out-group-probability
  ]
  
  if (potential-friend != nobody)
  [
     ;; Use friending-probability to impact chance of successfully becoming friends
     ;; Higher likelihood if they are in the same friend group, lower if they are not
     if ( (random-float 1.0 < friending-probability) and   
          (random-float max-friendship-factor < [friendship-tendency] of potential-friend) )
      [ create-friend-with potential-friend [ assign-link-color] ]
  ]
end 


;;; --------------------------------------------------------------------- ;;;
;;;
;;; COUPLING/UNCOUPLING PROCEDURES
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Agents might couple depending on their gender, their tendency to couple,
;; and if they are already friends/in same clique/nearby a potential single mate
;;
;; ----- Try to find a valid partner ----- ;;
;; 1) try existing friend link of opposite sex
;; 2) try opposite sex within friend group, but not a current link
;; 3) try a nearby opposite sex person as a last resort
;; (probability of successful coupling decreases for last 2 options)
;;

to couple ;; turtle procedure (single turtles only)
  ;; all my single turtles, now put your hands UP
  
  ;; This agent's clique (social/friend group) id
  let groupID group-membership
  
  ;; Probability that sexual partnership link will form
  ;; (arbitrary number to overwrite)
  let coupling-probability 1.0 
  
  ;; Probability of successful coupling decreases if the
  ;; potential friend is not part of the agent's clique
  ;; Note: these are arbitrary numbers that
  ;; could be adjusted for more realistic modeling
  let friend-probability 0.8
  let in-group-probability 0.6 ;.8
  let out-group-probability 0.3
 
  
  ;; Create variable that we will overwrite
  let potential-partner one-of friend-neighbors
  
  ;; For simplicity, only dealing with straight people (male + female pairs).
  
  ;; Try to find a valid potential sexual partner.
  ;; A valid potential sexual partner must be the opposite gender and not coupled.
  
  ;; Male agent - wants to find a female potential partner
  ifelse is-male? self
  [
    ;; First check out existing female friends
    set potential-partner (one-of females with [friend-neighbor? myself and not coupled?])
    set coupling-probability friend-probability
    
    ;; If that wasn't successful,
    ;; try to find a female within his clique that is not a current friend/link
    if (potential-partner = nobody)
    [
      set potential-partner
      (one-of females with [not link-neighbor? myself and not coupled? and group-membership = groupID])
      set coupling-probability in-group-probability
    ]
    
    ;; As a last resort,
    ;; look for the closest female that is not a link, even if they aren't in your clique
    if (potential-partner = nobody)
    [
      set potential-partner (min-one-of (females with [not link-neighbor? myself and not coupled?]) [distance myself])
      set coupling-probability out-group-probability
    ]
  ]
  
  ;; Female agent - wants to find a male potential partner
  [
    ;; First check out existing male friends
    set potential-partner (one-of males with [friend-neighbor? myself and not coupled?])
    set coupling-probability friend-probability
    
    ;; If that wasn't successful,
    ;; try to find a male within her clique that is not a current friend/link
    if (potential-partner = nobody)
    [
      set potential-partner
      (one-of males with [not link-neighbor? myself and not coupled? and group-membership = groupID])
      set coupling-probability in-group-probability
    ]
    
    ;; As a last resort,
    ;; look for the closest male that is not a link, even if they aren't in your clique
    if (potential-partner = nobody)
    [
      set potential-partner
      (min-one-of (males with [not link-neighbor? myself and not coupled?]) [distance myself])
      set coupling-probability out-group-probability
    ]
  ]
  
  ;; Finally, if they found a person who meets the above criteria,
  ;; Determine if potential partner is willing to couple with them
  if potential-partner != nobody
    [
      ;; Use coupling-probability to impact chance of successfully forming relationship
      ;; Highest likelihood if agents were already friends, lowest likelihood if agents weren't from same clique
      
       if ( (random-float 1.0 < coupling-probability) and   
          (random-float max-coupling-factor < [coupling-tendency] of potential-partner) )
        [
          set partner potential-partner
          set coupled? true
          ask partner
          [
            set partner myself
            set coupled? true
          ]
          
          ;; Change breed of link if friends,
          ;; and create link for sexual relationship regardless
          if (friend-neighbor? partner) [ask friend-with partner [die] ]
          create-sexual-partner-with partner [ assign-link-color]
        ]
    ]
end 


;;
;; If two persons are together for longer than either person's
;; commitment variable allows, the couple breaks up.
;;

to uncouple ;; turtle procedure (coupled turtles only)
  if coupled?
  [
    if (couple-length > commitment) or
      ([couple-length] of partner) > ([commitment] of partner)
      [
        ;; Break the link between these two turtles
        ;; assume they don't go back to being friends
        ask sexual-partner-with partner [die]
        
        ;; but if you wanted them to "just be friends"... uncomment line below
        ;create-friend-with partner [ assign-link-color]
        
        set coupled? false
        set couple-length 0
        ask partner
        [
          set couple-length 0
          set partner nobody
          set coupled? false
        ]
        set partner nobody
      ]
  ]
end 


;;; --------------------------------------------------------------------- ;;;
;;;
;;; INFECTING PROCEDURES 
;;;
;;; --------------------------------------------------------------------- ;;;

;;
;; Turtle becomes infected
;;

to become-infected ;; turtle procedure
  set infected? true
  assign-shape ;; infected turtles have a dot on their shape
  
  ; Note that the turtle will not "know" they are infected
  ; (and set the known? variable) until check-infected is called
end 


;;---------------------------------------------------------------------

;; In the next two procedures, users can infect an agent in the model
;; infect-random will choose a random agent, while select allows the 
;; user to choose an agent to infect with the mouse.
;; At least one function should be used at the beginning of the model run,
;; but they can be called at any time during the simulation

;; Note that in both of these procedures, the infected agent 
;; will not "know" they are infected until check-infected is called,
;; and even then, they will only be aware of their infected state
;; if his/her gender is symptomatic.

;; By doing it this way, the agents have a chance to spread the STI
;; before they realize they are infected

;;
;; Infect a random turtle (can do multiple times, if user wishes)
;;

to infect-random
  infect-random-female
  infect-random-male
  ;if (count turtles > 1)
  ;[
  ;  ask n-of 1 turtles with [not infected?]
  ;  [ become-infected ]
  ;]
end 

to infect-random-female
  if (count females > 1)
  [
    ask n-of 1 females with [not infected?]
    [ become-infected ]
  ]
end 

to infect-random-male
  if (count males > 1)
  [
    ask n-of 1 males with [not infected?]
    [ become-infected ]
  ]
end 

;;
;; User selects an agent in the model to infect with the mouse
;;

to select
  let picked? false
  if mouse-down?
  [
    let candidate min-one-of turtles [distancexy mouse-xcor mouse-ycor]
    if [distancexy mouse-xcor mouse-ycor] of candidate < 1
    [
        ask candidate
        [
          become-infected
          set picked? true
        ]
    ]
  ]
  if picked? [stop]
end 


;;; --------------------------------------------------------------------- ;;;
;;;
;;; CHECK-INFECTED PROCEDURE
;;;
;;; --------------------------------------------------------------------- ;;;

;;---------------------------------------------------------------------
;;
;; Turtle checks for signs of infection (symptoms)
;; Ideally don't want check-infect and become-infected happening on same tick
;; --> not realistic, std symptoms don't instantly show up
;; Otherwise, if not symptomatic, don't change their known? variable
;;

to check-infected
 
  ;; Justification decreases when an agent thinks they had unsafe sex 
  ;; and observes no negative consequences (i.e. didn't contract an STI,
  ;; or doesn't feel symptoms, regardless of whether s/he is actually infected).
  
  if ( had-unsafe-sex? and ( not infected? or
     (is-male? self and not males-symptomatic?) or
     (is-female? self and not females-symptomatic?) )
     )
  [ set justification (justification - justification-delta) ]

    
  ;; If an agent is infected and realizes it (due to being symptomatic)
  ;; Their likelihood of practicing safe sex increases significantly,
  ;; since we assume that agents are not malicious and intentionally infecting others
  
  if ((infected? and not known?) and
    ((is-male? self and males-symptomatic?) or
    (is-female? self and females-symptomatic?)))
  [
    set known? true
    set justification 100 ;; after getting an std, turtles always want to have safe sex - logical reason
    ;; direct experience is always more powerful at changing attitude than just talking about it
    set attitude 100 ;; also set their attitude towards safe sex to 100% positive
  ]
  
  update-safe-sex-likelihood 
  assign-turtle-color
  assign-shape ;; color of dot changes based on whether the agent knows they are infected
end 


;;; --------------------------------------------------------------------- ;;;
;;;
;;; REPORTER / MONITOR PROCEDURES
;;;
;;; --------------------------------------------------------------------- ;;;

to-report num-infected
  report count turtles with [infected?]
end 

to-report %infected
  ifelse any? turtles
    [ report 100 * num-infected / count turtles ]
    [ report 0 ]
end 

to-report %F-infected
  ifelse any? females
  [ report 100 * count females with [infected?] / count females]
  [ report 0 ]
end 

to-report %M-infected
  ifelse any? males
  [ report 100 * count males with [infected?] / count males]
  [ report 0 ]
end 


;; ----- Reporters for safe-sex-attitude measures ----- ;;

;; --------------- Safe sex likelihood  --------------- ;;
;; ------------- (condom use probability) ------------- ;;

to-report avg-safe-sex-likelihood
  report mean [safe-sex-likelihood] of turtles
end 

to-report avg-male-safe-sex-likelihood
  report mean [safe-sex-likelihood] of males
end 

to-report avg-female-safe-sex-likelihood
  report mean [safe-sex-likelihood] of females
end 

  ;; Determine how much this agent's likelihood of practicing safe sex
  ;; has changed since last tick.
  ;; (If likelihoods of all agents stop changing significantly,
  ;; the simulation will stop.)

;; --------------- Attitude --------------- ;;

to-report avg-attitude
  report mean [attitude] of turtles
end 

to-report avg-male-attitude
  report mean [attitude] of males
end 

to-report avg-female-attitude
  report mean [attitude] of females
end 

;; --------------- Certainty --------------- ;;

to-report avg-certainty
  report mean [certainty] of turtles
end 

to-report avg-male-certainty
  report mean [certainty] of males
end 

to-report avg-female-certainty
  report mean [certainty] of females
end 

;; --------------- Justification --------------- ;;

to-report avg-justification
  report mean [justification] of turtles
end 

to-report avg-male-justification
  report mean [justification] of males
end 

to-report avg-female-justification
  report mean [justification] of females
end 

;;
;; Not all reporters need be displayed in the model (to avoid information overload),
;; but readily available if the user wishes to add monitors
;; to view additional demographic information
;;

;; Begin somewhat unnecessary reporters that were at one point used for debugging-ish


;; --------------- Change in likelihood between ticks --------------- ;;

;; Note: take absolute value, otherwise if some turtles are
;; very positively increasing and others are very negatively decreasing,
;; could result in calculating like there is no change occurring

to-report avg-likelihood-change
  report mean [ abs (safe-sex-likelihood - old-safe-sex-likelihood)] of turtles
end 

to-report avg-male-likelihood-change
  report mean [abs (safe-sex-likelihood - old-safe-sex-likelihood)] of males
end 

to-report avg-female-likelihood-change
  report mean [abs (safe-sex-likelihood - old-safe-sex-likelihood)] of females
end 

;; originally used above measures for a plot,
;; but it wasn't very interesting given the space it took up

to-report avg-friends-per-turtle
  report mean [count friend-neighbors] of turtles
end 

to-report avg-partners-per-turtle
  report mean [count sexual-partner-neighbors] of turtles
end 

to-report num-in-group-friends
  report count friends with [
    ([group-membership] of end1 = [group-membership] of end2 )]
end 

to-report num-out-group-friends
  report count friends with [
    ([group-membership] of end1 != [group-membership] of end2 )]
end 

to-report num-in-group-partners
  report count sexual-partners with [
    ([group-membership] of end1 = [group-membership] of end2 )]
end 

to-report num-out-group-partners
  report count sexual-partners with [
    ([group-membership] of end1 != [group-membership] of end2 )]
end