If I'm infected then individuals I randomly encounter may become infected. The odds of encountering anyone is heavily biased to those nearby.

Begin micro-behaviour

RANDOM-SPATIAL-ENCOUNTER

Begin NetLogo code:
substitute-text-area-for odds-of-encountering 1 / (1 + distance-to-me ^ 2) > random-number-between 0 1
do-every 1
   [do-if my-state = "infected" 
       [do-for-n the-encounter-rate
                 all-individuals with 
                  [my-state != "dead" and 
                   odds-of-encountering]
          [set my-last-encounter the-other
           add-behaviours list-of-micro-behaviours "Encounter Behaviours" [POSSIBLE-INFECTION.html]]]]
End NetLogo code

Variants

A different formula for biasing the odds to nearby individuals can be used. Additional encounter behaviours can be added.

Related Micro-behaviours

This relies upon the POSSIBLE-INFECTION micro-behaviour to possibly infect the other. CREATE-ENCOUNTER-RATE-SLIDER defines the-encounter-rate variable used here.

RANDOM-ENCOUNTER is like this micro-behaviour without a spatial bias.

RANDOM-SOCIAL-ENCOUNTER chooses individuals among my set of acquaintances.

RANDOM-PHYSICAL-ENCOUNTER chooses individuals that are at my location.

How this works

This models individuals that have the-encounter-rate encounters per unit time period (e.g., a simulated week). Every second, if I'm still infected (i.e., my-state = "infected") then I pick the-encounter-rate  other individuals (who are not dead) . Individuals are picked with a probability that is inversely proportional to the square of the distance to me. I give these individuals the micro-behaviour POSSIBLE-INFECTION. The formula adds 1 to avoid a division by zero if someone is co-located with me. If the-encounter-rate is a non-integer then the remainder is compared with a random number probabilistically to possibly include one additional individual. I also sets the my-last-encounter variable of the other individuals to me in order to keep track of how many infections I cause.

do-for-n selects n agents and sets the-other to refer to each one.

History

This was implemented by Ken Kahn.