NetLogo User Community Models
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## WHAT IS IT?
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;
* Once in 50 years, in the year of Jubilee, all lands returned to the original owners.
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. By default they are equal, but this can be changed.
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.
* equal land division - each citizen gets a single land plot in turn, until there are no more lands left.
* give all lands to a single citizen (n citizens, where n=1).
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.
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 several options:
* no-jubilee - nothing is done;
* jubilee-to-landless - each citizen with no land picks one of the lands that he had in the previous Jubilee (if any), and gets it back.
* jubilee-from-landowners - each citizen with more than one land picks one of the lands that he wants to keep, and returns all other lands to their owners in the previous Jubilee.
* jubilee-to-landless-from-landowners - each land, whose current owner has more than oen land, and whose previous owner has no land, is returned from the current owner to the previous owner.
* jubilee-for-all - each citizen gets all lands that he had in the previous Jubilee.
The Jubilee procedures involve some uncertainty, as the buyer does not know in advance whether the seller will be entitled to claim his land back at the Jubilee. The **reduced-uncertainty** switch allows to reduce this uncertainty in some cases: if the buyer had no other land at the initial period, and the seller had other lands, then the deal can be made permanent right now, without affecting the properties of the Jubilee algorithm.
After the Jubilee, the trade goes on as before. The simulation stops after **last-period** periods.
## HOW TO USE IT
Choose the number of citizens, the number of lands, the probability of deal per period, the number of periods per Jubilee, the total number of periods, the initial division procedure, and the Jubilee procedure. Then click **setup**.
Pressing the **go once** button will run a single period. Some lands will be sold to new owners. A directed link points from the original owners to the new owner. The color of the land will change to that of the 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 number of deals canceled is shown in the **deals canceled** plot.
## THINGS TO NOTICE
When the Jubilee procedure is **jubilee-to-landless** or **jubilee-from-landowners**, 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 where all citizens have land (as long as the number of lands is not less than the number of citizens).
To see this more clearly, set the periods-per-jubilee to 1.
This apparently does not happen for **no-jubilee** or **jubilee-for-all**.
When the Jubilee procedure is **jubilee-to-landless-from-landowners**, the number of landless citizens initially decreases, but then stops decreasing and begins fluctuating. This procedure does NOT guarantee that the number of landless will not increase!
## THINGS TO TRY
How many Jubilees it takes until each citizen has a land?
How does the answer depends on the probability-of-deal?
How does the answer depends on the num-of-lands?
Try setting **periods-per-jubilee** to 1 and **probability-of-deal** to 1.0, and see how the number of landless decreases.
How does the number of deals canceled change, as more and more citizens have land?
If originally ALL citizens have land, is it still possible that some deals will NOT be canceled in the Jubilee year? What is required for this to happen? (hint: look for cycles in the graph at period 0).
## EXTENDING THE MODEL
Right now the probability of any land being sold is identical. Can you think of more realistic models?
Perhaps the model should also include wealth; wealthy citizens are more likely to buy lands, while poor citizens are more likely to sell lands.
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.
## 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, and are colored in the same color as their current owner.
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.
## 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:
- Segal-the-Levite Erel (2012). NetLogo Land-Random model. http://ccl.northwestern.edu/netlogo/models/community/land-random.
- Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.
## COPYRIGHT AND LICENSE
Copyright 2012 Erel Segal the Levite.
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.
