Luciano Pomatto, Alberto Vigada

Computer Science and Simulation for Economics

Project work on



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.

created with NetLogo

view/download model file: demography.nlogo


This project simulates demopraphic crisis in a closed economy with no growth, in line with the classic, Malthusian, theory. Our purpose is to emulate simple population trends in a pre-industrial society.
Agents in this model are families: their goal is to maximize family income, in order to do so they bear children, according to their fertility. Total income is fixed (and normalized to 1) and every person earn a fraction of it equal to 1/population.

When income is below a threshold every family run the risk of starting a terrible plague. Every infect family can infect closer families.


Click the setup button to set up the families.
Click the go button to start the simulation.
With the slider FERTILITY you can choose how may children each family can bear at the beginning of every period. The slider DENSITY controls the "urban" density, while PROBABILITY OF CONTAGION control how much the plague in dangerous.
Turning on SHOW-LABEL you can see how many people live in every family.


During every period in each infect family (red) 4 people die, and every person in the economy can die under a probability equal to MORTALITY.
Mortality is inversely proportional to income. When in a family live more than ten people, two of them start a new one.


Setting the slide PROBABILITY OF CONTAGION to zero is a nice experiment. Do the population rises forever?
Manipulating the sliders you can see under which conditions the population is doomed to extinction.


The biggest limit of this model is that agents don't learn anything from the plague (how to protect themselves and their family from a new one). It would be interesting to study under which conditions families can coordinate and limit the number of children in every period, in order to keep the income level high enough.