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3. Added microsimulation features

The Schelling model is an example of a simple theoretical (“toy”) AB model: the focus is on the externality mechanism, rather than on empirical veracity.

In our implementation, we have modified it to include a basic feature of dynamic microsimulations: a population that evolves in time according to some specified processes. Accordingly, gender is specified for every individual in the population, and external birth probabilities (for women aged 15-50) and death probabilities (differentiated by gender) are loaded.

These probabilities, stored in the MS Excel files p_birth.xls, p_death_m.xls and p_deat_f.xls, are age and year specific, with year running from 2002 (the initial year of the simulation) to 2060. They are taken from the LIAM2 demo models, and are therefore representative of the real birth and death probabilities in a continental European country.

For the sake of illustration, the initial population can either be loaded from an external database (input.h2) or built synthetically “on the fly”.

In the example, the loaded population (5,000 individuals) is not representative of any real population: in particular, age is uniformly distributed between 20 and 30, and location is random: think of a population of new settlers on a greenfield. The loaded population is located on a 120*120 grid (14,400 cells): the grid is therefore only sparsely populated at the beginning of the simulation. The demographic dynamics applied to the young initial population lead to rapid population growth and then stabilization around 11,000 individuals.

Newborns are located in an empty cell as close to their mother as possible (search occurs in a concentric manner), with no constraints on neighborhood composition. If no free cells are available, both the newborn and the mother leave the city. For simplicity, the connection between newborns and their mothers is disrupted after their first period of existence. Unsatisfied individuals also look for a suitable location in a concentric manner starting from their current location, and leave the city if they cannot find one. Finally, individuals aged 65 and over and women who have just given birth to a baby cannot move.

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