Micro Macro representation

Purpose

This demonstration illustrates relationships between a two-level phenomenon where emergence and immergence relationships occur.
We use a two-level representation of a flocking phenomenon system:

• at micro level are the birds

• at macro level are the flocks

Principles of demos

We propose 3 demos with flocking. Each of them illustrated an aspect of coupling between the levels of representation.
Initially, at micro leve the system starts with birds located randomly. The macro level is empty (no flock has emerged).
At micro level, birds evolve according to the flocking rules of Netlogo model.
At each time step, birds positions are collected and flocks are detected and passed to the macro level where they are represented as Netlogo turtles (with a radius).
According to the demo, different modeling schemes are used:

1. coloring: groups have no dynamics (no behavior applies) they are only represented with different colors. When birds  (micro level) are part of a flock (macro level) they are coloredthe same.
2. downward effect: groups have a dynamic (they evolve according to behavioral  rules) that modifies their position. The movement vector at macro level is used to move birds at micro level. This obliges to modify micro level dynamics: birds in a flock move according to the displacement vector computed at macro level.
3. downward effect with different time scales: in this case, we have the same principle as the previous one, except that when we simulate ONE time step at macro level, this corresponds to FOUR time steps at micro level.