Introduction

Insects that live in colonies— ants, bees, wasps, termites — have long fascinated everyone from naturalists to artists.

Each insect in a colony seems to have its own agenda, and yet the group as a whole appears to be highly organized. Apparently, the seamless integration of all individual activities does not require any supervision. In fact, scientists who study the behaviour of social insects have found that cooperation at the colony level is largely self-organized: in numerous situations the coordination arises from interactions among individuals.

Although these interactions might be simple (one ant merely following the trail left by another), together they can solve difficult problems (finding the shortest route among countless possible paths to a food source). This collective behavior that emerges from a group of social insects has been dubbed “swarm intelligence.”

In swarm intelligence, the whole > the sum of the parts. Complex tasks can be tackled only through cooperation of the multitude. The intelligence is in the group.

The outcome of the effort comes at a group level:

• The single parts may not be aware of the bigger goal.
• There is no leader or centralized coordination.
• Interaction/coordination happens at a microlevel.
  • Direct: through senses.
  • Indirect: through changes in the environment.

Computational swarm intelligence:

• Algorithms that define simple individual behavior modulated by simple interactions between individuals
• Emergent group behavior.

Focus on the individual actors, not on the whole system (which might be too complex to model)

We will focus on two methods: Ant Colony Optimization (ACO) and Particle Swarm Optimization (PSO). Usually:

• ACO → Combinatorial optimization (e.g. routing)
• PSO → Continuous optimization (e.g. control)

Ant Colony Optimization (ACO)

Ant colony optimization(ACO) was first introduced by Marco Dorigo in the 90s in his Ph.D. thesis. This algorithm is introduced based on the foraging behaviour of an ant for seeking a path between their colony and source food.

Ants are social insects. They live in colonies. The behaviour of the ants is controlled by the goal of searching for food. While searching, ants roaming around their colonies. An ant repeatedly hops from one place to another to find the food. While moving, it deposits an organic compound called pheromone on the ground. A pheromone is a secreted or excreted chemical factor which enables ants to effectively explore the environment.