Chapter 1: From Real to Artificial Ants

Background

• Marco Dorigo's website
• Thomas Stützle's website
• A video entitled Ants: Nature's Secret Power
• A video entitled How Do Ants Know What to Do? (thanks to Nick Howard)

Terminology

• Stigmergy: communication by modifying the environment - pheromone trails
• Autocatalytic feedback: positive feedback
• Convergence: the probability of a selected path becoming arbitrarily close to 1

Artificial Ant Ingredients

• Probabilistic solution construction based on pheromone trails
• Limited form of memory
• Deterministic pheromone trail update based on solution quality
• Pheromone trails decay over time
• Exploration vs. Exploitation tradeoff

S-ACO: Simple Ant Colony Optimization

• Equation 1.8: probability of selecting a particular trail
• Equation 1.9: pheromone update
• Equation 1.10: pheromone decay
• Table 1.1: importance of using path length in pheromone update
• Figure 1.10: importance of a proper decay setting
• In general, parameter settings (such as α) are important for good results