Swarm Intelligence - an Overview and Relevance to Bioinformatics

The behavior of a single ant, bee, termite and wasp often is too simple, but their collective and social behavior is of paramount significance. A look at National Geographic TV Channel also reveals that advanced mammals including lions also enjoy social lives, perhaps for their self-existence at old age and in particular when they are wounded. The collective and social behavior of living creatures motivated researchers to undertake the study of swarm intelligence. Historically, the phrase

Swarm Intelligence (SI) was coined by Beny &Wang in late 1980s in the context of cellular robotics. A group of researchers in different parts of the world started working almost at the same time to study the versatile behavior of different living creatures. SI systems are typically made up of a population of simple agents (an entity capable of performing/executing certain operations) interacting locally with one another and with their environment. Although there is normally no centralized control structure dictating how individual agents should behave, local interactions between such agents often lead to the emergence of global behavior.

Creatures such as fish schools and bird flocks clearly display structural order, with the behavior of the organisms so integrated that even though they may change shape and direction, they appear to move as a single coherent entity. The main properties of the collective behavior can be given below.

• Homogeneity: every bird in flock has the same behavioral model. The flock moves without a leader, even though temporary leaders seem to appear.

• Locality: its nearest flock-mates only influence the motion of each bird. Vision is considered to be the most important senses for flock organization.

• Collision avoidance: avoid colliding with nearby flock mates.

• Velocity matching: attempt to match velocity with nearby flock mates.

• Flock centering: attempt to stay close to nearby flock mates.

Individuals attempt to maintain a minimum distance between themselves and others at all times. This rule is given the highest priority and corresponds to a frequently observed behavior of animals in nature. If individuals are not performing, an avoidance manoeuvre they tend to be attracted towards other individuals (to avoid being isolated) and to align themselves with neighbors identified four collective dynamical behaviors

• Swarm: an aggregate with cohesion, but a low level of polarization (parallel alignment) among members.

• Torus: individuals perpetually rotate around an empty core (milling). The direction of rotation is random.

• Dynamic parallel group: the individuals are polarized and move as a coherent group, but individuals can move throughout the group and density and group form can fluctuate.

• Highly parallel group: much more static in terms of exchange of spatial positions within the group than the dynamic parallel group and the variation in density and form is minimal.

At a high-level, a swarm can be viewed as a group of agents cooperating to achieve some purposeful behavior and achieve some goal. This collective intelligence seems to emerge from what are often large groups of relatively simple agents.

The agents use simple local rules to govern their actions and via the interactions of the entire group, the swarm achieves its objectives. A type of self-organization emerges from the collection of actions of the group.

An autonomous agent is a subsystem that interacts with its environment, which probably consists of other agents, but acts relatively independently from all other agents. The autonomous agent does not follow commands from a leader, or some global plan. For example, for a bird to participate in a flock, it only adjusts its movements to coordinate with the movements of its flock mates, typically its

neighbors that are close to it in the flock. A bird in a flock simply tries to stay close to its neighbors, but avoid collisions with them. Each bird does not take commands from any leader bird since there is no lead bird. Any bird can in the front, center and back of the swarm. Swarm behavior helps birds take advantage of several things including protection from predators (especially for birds in the middle of the flock), and searching for food (essentially each bird is exploiting the eyes of every other bird).

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