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We model a society with three types of people: cooperative citizens, greedy citizens and stealers. The first two groups try to defend themselves from the third. We investigate how the difference in behaviour (cooperative or not) affects aggregate income.

The two groups of citizens have income which is given according to a normal distribution. Then cooperative citizens tax themselves, and with the revenues pay policemen (chosen among low income profiles in their group). Greedy citizens buy weapons, but not everyone can afford the expense. Both groups then invest their net incomes in the financial markets. Stealers take citizen’s income with a certain probability, this depends on weapons and on the presence of policemen in the neighbourhood.

Stealers can reproduce exceeded a certain amount of robbery, but the threshold increases exponentially with the amount of stealers. When stealers meet cops they loose the booty, which will be counted as aggregate income for cooperative citizens.

Press Setup button:

- incomes are distributed, cooperative citizens below a threshold become cops

- weapons are buyed and tax collected

Press Go button:

- agents start moving and stealers take others income with a certain probability

Important variables:

-Aggregatecit = measures invested income of cooperative citizens plus wage of cops and booty seized to stealers

-Aggregreedy = measures invested income of greedy citizens

-Aggregaterobberycit= amount of robbery stolen to cooperative citizens

-Aggregaterobberygreed = amount of robbery stolen to greedy citizens

Changes in these variables allow to understand which group is facing better the threat of stealers.

Sliders:

- Amount of cooperative and greedy citizens can be changed, as also the number of stealers.

- Mean value and standard deviation of the normal distribution of incomes. Interest rates at which citizens invest.

-Price of weapons: a fixed cost component as also a marginal cost component.

-Thresholds: the one under which cooperative citizens become cops and the one above which stealers reproduce themselves.

In order to make our inferences more applicable to reality, an implementation could be rethinking the entire model introducing values for the parameters closer to empiric ones. Our last experiment is just a first attempt in this direction. For example we could introduce microlevel data, describing places and daily activities of individuals, in order to represent their usual habits of movements.

breed [stealers stealer] breed [cops cop] breed [greedy-citizens greedy-citizen] breed [friendly-citizens friendly-citizen] globals [ farest-stealer victim aggrecit collectedtax aggregaterobberycit aggregaterobberygreed aggregreedy aggregatetreasure aggregaterobbery aggregatewage price reproduction-threshold ] friendly-citizens-own [initincome tax netincome income] greedy-citizens-own [initincome netincomeg incomeg] ;; price e total-stealers non "appartengono" ai greedy citizens, come toglierle? stealers-own [robberycit robberygreed robbery netincome netincomeg income incomeg] cops-own [initincome netincome wage income tax treasure] to setup clear-all setup-stealers setup-friendly-citizens setup-greedy-citizens setup-cops set aggrecit sum [income] of friendly-citizens set aggregaterobberycit sum [robberycit] of stealers set aggregaterobberygreed sum [robberygreed] of stealers set aggregaterobbery sum [robbery] of stealers set aggregreedy sum [incomeg] of greedy-citizens set aggregatewage sum [wage] of cops set collectedtax sum [tax] of friendly-citizens set reproduction-threshold intercept-reproduction ask patches [ set pcolor white ] reset-ticks end to setup-stealers set-default-shape stealers "wolf" create-stealers number-stealers [set color black setxy random-xcor random-ycor] ask stealers [set robberycit 0 set robberygreed 0 ] end to setup-friendly-citizens set-default-shape friendly-citizens "person" create-friendly-citizens number-friendly-citizens [ set color red setxy random-xcor random-ycor ] ask friendly-citizens [set initincome random-normal value-mean value-deviation set tax trate * initincome set netincome (initincome - tax) set income netincome ] end to setup-greedy-citizens set-default-shape greedy-citizens "person" create-greedy-citizens number-greedy-citizens [ set color blue setxy random-xcor random-ycor ] ask greedy-citizens [set initincome random-normal value-mean value-deviation set price number-stealers * initcost + number-stealers * marginalcost set netincomeg (initincome - price) ifelse netincomeg > 0 [set incomeg netincomeg] [set incomeg initincome] ] ;; provare differenziare robbery end to setup-cops ask friendly-citizens [ifelse initincome <= copthreshold [set breed cops set color green setxy random-xcor random-ycor set wage income set treasure 0 ] [set breed friendly-citizens] ] end to go ask turtles [move-turtles] ask friendly-citizens [invest-cit] ask greedy-citizens [invest-greedy] ask cops [invest-cop] ask stealers[ steal reproduce] update-variables if all? greedy-citizens [incomeg = 0] or all? friendly-citizens [income = 0] [stop] tick end to move-turtles right random 360 forward 1 end to invest-cop set wage wage + collectedtax / count cops end to invest-cit set income income + income * interestfriendly - (income * interestfriendly) * trate set tax (income * interestfriendly) * trate end to invest-greedy set price count stealers * marginalcost ifelse incomeg > 0 [set incomeg incomeg + incomeg * interestgreedy - (price)] [set incomeg 0] end to steal set victim max-one-of turtles [distance myself] ask victim [ set farest-stealer max-one-of stealers [distance myself] ask farest-stealer [if [breed] of myself = greedy-citizens [if sum [count cops] of neighbors4 >= 1 and [netincomeg] of myself >= 0 [ifelse random-float 1.0 <= 0.3 [set robberygreed robberygreed + [incomeg] of myself ask victim [set incomeg 0] ] [set robberygreed robberygreed]] if sum [count cops] of neighbors4 < 1 and [netincomeg] of myself >= 0 [ifelse random-float 1.0 <= 0.7 [set robberygreed robberygreed + [incomeg] of myself ask victim [set incomeg 0] ] [set robberygreed robberygreed]] if sum [count cops] of neighbors4 >= 1 and [netincomeg] of myself < 0 [ifelse random-float 1.0 <= 0.5 [set robberygreed robberygreed + [incomeg] of myself ask victim [set incomeg 0] ] [set robberygreed robberygreed]] if sum [count cops] of neighbors4 < 1 and [netincomeg] of myself < 0 [ifelse random-float 1.0 <= 0.9 [set robberygreed robberygreed + [incomeg] of myself ask victim [set incomeg 0] ] [set robberygreed robberygreed]] ] if [breed] of myself = friendly-citizens [if sum [count cops] of neighbors4 >= 1 [ifelse random-float 1.0 <= 0.5 [set robberycit robberycit + [income] of myself ask victim [set income 0]] [set robberycit robberycit]] if sum [count cops] of neighbors4 < 1 [ifelse random-float 1.0 <= 0.9 [set robberycit robberycit + [income] of myself ask victim [set income 0] ] [set robberycit robberycit] ]] if [breed] of myself = cops [ ask victim [ set treasure treasure + [robberycit] of myself + [robberygreed] of myself set wage wage + treasure ask farest-stealer [set robberycit 0 set robberygreed 0]] ] ] ] end to reproduce if robberygreed >= reproduction-threshold or robberycit >= reproduction-threshold [ hatch 1 [lt 45 fd 1] ] end to update-variables set aggrecit sum [income] of friendly-citizens print aggrecit set aggregreedy sum [incomeg] of greedy-citizens print aggregreedy set aggregatetreasure sum [treasure] of cops print aggregatetreasure set collectedtax sum [tax] of friendly-citizens print collectedtax set aggregaterobberycit sum [robberycit] of stealers print aggregaterobberycit set aggregaterobberygreed sum [robberygreed] of stealers print aggregaterobberygreed set aggregaterobbery aggregaterobberygreed + aggregaterobberycit print aggregaterobbery set aggregatewage sum [wage] of cops print aggregatewage ifelse count stealers >= number-friendly-citizens [set reproduction-threshold exp((count stealers)^ 0.5) - exp((count stealers)^ 0.10)] [set reproduction-threshold intercept-reproduction] end