Laura Cosa Livio Nervo Federico Volpe

Computer Science and Simulation for Economics

Project work on

"The Jak Bank case."


The applet requires Java 1.4.1 or higher. It will not run on Windows 95 or Mac OS 8 or 9. Mac users must have OS X 10.2.6 or higher and use a browser that supports Java 1.4. (Safari works, IE does not. Mac OS X comes with Safari. Open Safari and set it as your default web browser under Safari/Preferences/General.) On other operating systems, you may obtain the latest Java plugin from Sun's Java site.

powered by NetLogo

view/download model file: the_Jak_Bank_case.nlogo


The model simulates the functioning of the Jak Bank, based on saving points accumulation. This is a Swedish cooperative bank which grants small entity loans to its members. The system allows to obtain a loan if a family hasn't accumulate enough saving points; in this case it must look to a post-saving loan in order to respect the parity between gained and used points. The only interest applied is a loan fee calculated as a percentage on the borrowed amount.
Our aim is to monitor the behaviour of the bank and members, also during economic shocks.


The bank in the model is represented by two branches: yellow patches stand for the deposit section while the white ones stand for the loan section. The families, all blue at the beginning, start walking with random movements and if they walk on the bank they can make a deposit (yellow area) or get a loan (white area). From the first deposit members begin to accumulate saving points and when they require a loan two situations can occur:
- if the family has enough points it gets a basic loan and turns orange,
- otherwise it gets a post-saving loan and turns red; in this case it must continue to save money and its repayment is bigger.
Then members pay back their debts and they turn blue just when have finished.
During an economic shock situation, families change their shape in ghosts and couldn't pay back repayments causing problems to the bank.


Start the simulation by clicking "Setup". Then, after clicking "Go", the turtles start moving and interacting in the way explained above; they keep on doing so until the "Go" button remains pressed. Instead by clicking "Step" the model runs only one cycle of the simulation.

Button: Setup
Resets everything to the beginning values and creates turtles
(families) and patches (sections of the bank).

Button: Go
If clicked, the model starts running.

Button: Step
If clicked, the model runs only one cycle of the simulation.

Botton: Schock
If clicked, the number of families set by the slider shock_intensity is struck by an economic shock.

Button: Stop shock
This button stops the economic shock situation.

Slider: number_of_families
This slider allows you to choose the number of families you would like to begin the simulation with in a range from 20 to 100, with an increase of 10.

Slider: saving_factor
This slider allows to change the saving factor, a number by witch deposited money is translated in saving points.

Slider: loan_fee
This slider can be used to modify the loan fee applied by the bank to its members.

Slider: estimated_percentage_of_borrowers:
With it you can change the number of borrowers expected by the bank.

Slider: shock_intensity
With it you can decide the number of families struck by the shock

Monitor: post saving families
This monitor shows the number of families which are paying back a loan by making post-saving (red turtles)

Monitor: basic loan families
It reports the number of families which are paying back a basic loan (orange turtles)

Monitor: families without loan
It shows the number of families which don't have an open position with the bank

Monitor: shocked families
This monitor reports the number of families struck by an economic shock

Monitor: default families
It shows the number of families which can't pay back repayments

Plot: Bank situation
This plot reports the trend of three bank's variables: deposit_account, liquidity and reserve


It is important to notice that for a long period the number of post saving loans remains higher than basic loans; in fact the system is based on post saving while the basic loan is just a particular case because few families have enough points to get it.
Moreover it could be interesting to observe the graph of the bank situation. You can notice that, in a default condition, from about 6 to 11 years (72 - 132 ticks) the liquidity is characterised by a period of fluctuation within a narrow margin and with no overall direction. The fluctuation begins when the bank starts the activity of lending money and it takes some years to accumulate new liquidity.


It is interesting to modify the values of the sliders, especially combining the saving factor and the loan fee in different ways. In addition to this you can determine an economic shock, decide its duration and its impact on the families.


When the bank grants a loan it could be interesting to add the role of guarantors.
We could also improve our model with the presence of companies as bank's members.


Enrico Longo, President of "Associazione Culturale Jak Bank Italia";
Giorgio Simonetti, journalist and author of the book "Jak Bank, per un modello finanziario sostenibile libero dal concetto di usura";
Miguel Ganzo, International relations coordinator at JAK Medlemsbank