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## NetLogo User Community Models

## WHAT IS IT?

This model represents the formation of a network of friendships between agents; friendship can end naturally or badly, and in the latter case agents may die.

## HOW IT WORKS

There is a certain number of nodes, disposed in a circle. Each of them has a "behavioral predisposition" (say, how much they like ice cream!) that goes from 0 to 10. This predisposition is uniformly randomly assigned. The nodes all start with a given "happiness level".

Each turn, at random, nodes are matched two-by-two. If they like ice cream to a similar level (let's say, the difference between their behavioral predispositions is less than 2) they become a friend, forming a link. This friendship is stronger the lower the difference between behavioral predispositions, and when it is formed it gives both nodes a fixed increase in their happiness level.

Friendships last for 5 turns, after which they end painlessly (nodes get bored easily!). But here comes the trick: in each turn, with a small probability, a friendship can end abruptly (say, the two friends fight over the ice cream flavor) and this causes a big loss of happiness (nodes are very sensitive!). If the happiness level goes to 0, then the node dies, and this cuts all the friendship it has (you can't be friend with a dead guy, can you?) possibly causing a cascade of deaths. Yup, it's a sad model, indeed.

## HOW TO USE IT

starting_happiness: the starting level of happiness of all the agents

increase_in_friendship: the increase in happiness stemming from a new friendship

beh_pred_range: the range of possible tastes of agents (which are uniformly distributed across them)

max_distance_for_friendship: the max difference in behavioral predispositions for two agents to become friends

prob_fight: the probability of a friendship ending abruptly at any given tick

loss_if_fight: the decrease in friendship stemming from a fight, or from the death of a friend

expiration_time: the number of ticks a friendship can last; it will end peacefully after that

## THINGS TO NOTICE

(suggested things for the user to notice while running the model)

## THINGS TO TRY

(suggested things for the user to try to do (move sliders, switches, etc.) with the model)

## EXTENDING THE MODEL

(suggested things to add or change in the Code tab to make the model more complicated, detailed, accurate, etc.)

## NETLOGO FEATURES

(interesting or unusual features of NetLogo that the model uses, particularly in the Code tab; or where workarounds were needed for missing features)

## RELATED MODELS

(models in the NetLogo Models Library and elsewhere which are of related interest)

## CREDITS AND REFERENCES

(a reference to the model's URL on the web if it has one, as well as any other necessary credits, citations, and links)