NetLogo User Community Models
by Erel Segal Halevi (Submitted: 04/11/2012)
## WHAT IS IT?
This is an elaboration of the [land-random model](http://ccl.northwestern.edu/netlogo/models/community/land-random), that takes differences in income into account.
Citizens gain income from several sources - some depend on land while others do not. Citizens buy land with probability that is directly proportional to their wealth - the rich are more probable to buy land than the poor. Can the Jubilee still help the poor get some land?
Freedom, in Biblical economy, means that every citizen owns a land-plot. Originally, this was achieved by two means:
* Initially, all land was divided into equal plots, and each citizen got a plot;
This model checks whether it is possible to achieve the goal of Freedom (meaning, every citizen owns a land) even when the initial division is not equal.
## HOW IT WORKS
There are **num-of-citizens** citizens, and **num-of-lands** land-plots.
Initially, land is divided in a way defined by the **initial-land-division** menu. There are several options:
* random land division - each land goes to a citizen selected at random. This means that some citizens will have no land, while others will have many plots.
At each period, each citizen gains some income. The income comes from several sources:
* A. Work - each citizen gets some salary per period, regardless of land ownership. The salary of a citizen is chosen in the beginning from a log-normal probability distribution (cf. F. Clementi and M. Gallegati, "Pareto's law of income distribution: Evidence for germany, the united kingdom, and the united states," EconWPA, 2005). The parameters of the lognormal distribution are calculated from **income-from-work-mean**, and from **income-from-work-equality**, which is defined as median/mean. Additionally, each period there is a chance that a citizen's income will change - this chance is **income-from-work-mobility**. In case a citizen's income changes, the system will select a new income at random, from the same log-normal distribution.
At each period, each land has some probability of being sold: the **probability-of-deal-per-period** slider. If a land is sold, it is transferred to a citizen picked at random, where the probability of each citizen to be the buyer is proportional to his/her wealth.
After 50 periods (or a different number, set by the **periods-per-jubilee** slider), a Jubilee procedure is performed, as defined by the **jubilee-procedure** menu. There are 3 options:
* no-jubilee - nothing is done;
After the Jubilee, the trade goes on as before. The simulation stops after **last-period** periods. A
lternatively, you can use the **num-of-runs** slider to run the simulation several times, and calculate the mean and std of the number of landless citizens at the last-period. These values will be printed in the output window, as a tab-seperated line.
## HOW TO USE IT
Choose the number of citizens and lands, the probability of deal per period, the number of periods per Jubilee, the Jubilee procedure, and the value of each income component. Then click **setup**.
Pressing the **go once** button will run a single period.
The wealth of the citizens changes. The color of the citizens changes according to their wealth - wealthier citizens will have brighter colors.
The wealth distribution is shown in the "wealth distribution" plot.
Some lands will be sold to new owners. A directed link points from the original owner to the new owner. The brightness of each land will match the brightness of its new owner.
The land distribution is shown in the "land distribution" histogram and the "landless" plot.
As the model runs, there are more and more links. But at the Jubilee year, some or all lands return to their original owner, so some or all links are removed.
The percentage of deals canceled is shown in the "deals canceled" plot.
## THINGS TO NOTICE
When the Jubilee procedure is "jubilee-for-landless", the number of landless citizens decreases in each Jubilee, relative to the previous Jubilee. Over time, all citizens will have land. The land distribution approaches the state of a single land per citizen.
To see this more clearly, set the probability-of-deal to 1.0, and the periods-per-jubilee to 1.
This does not happen for "no-jubilee" or for "jubilee-for-all".
## THINGS TO TRY
Change the **income-from-work** to 0, and restart. Is it still true that all citizens eventually have land?
Increase the income-from-work gradually. How does this affect the speed in which the system converges?
After convergence, decrease the income-from-work to 0 again. Does this affect the land distribution?
Play with the other income components - **income-from-agriculture**, **income-from-rent** and **income-from-welfare**. Do they have any effect?
## EXTENDING THE MODEL
Perhaps the model should also include subjective prerefences: some citizens prefer to live in the east, while others prefer to live in the west. etc.
Currently, the land price is ignored - land is just transfered from the seller to the buyer for free. In Biblical times, the land price was calculated as the annual income from the land, times the number of years remaining until the coming Jubilee.
## NETLOGO FEATURES
Citizens are turtles. Land-plots are patches. However, since there are usually more patches then turtles, only some of the patches are considered for the model. They are called "land-patches" in the code.
Links are used to link the original owner of a land with its current owner. A cycle, in that graph, means that the relevant owners switched their lands.
A utility function, "one-of-biased", is used to select a buyer: it gets as input an agentset and a reporter, and selects one agent at random, with probability proportional to the value that the reporter reports for it. In our model, the reporter simply returns the wealth of the citizen, so that probability of buying land is proportional to wealth.
## HOW TO CITE
If you mention this model in a publication, we ask that you include these citations for the model itself and for the NetLogo software:
## COPYRIGHT AND LICENSE
Copyright 2012 Erel Segal the Levite.
![CC BY-SA 3.0](http://i.creativecommons.org/l/by-sa/3.0/88x31.png)
This work is licensed under the Creative Commons Attribution-ShareAlike 3.0 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.
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