Complexity: A Very Short Introduction (Very Short Introductions)

• self-organization into patterns, as occurs with flocks of birds or schools of fish

This perpetual novelty, produced with a limited number of rules or laws, is a characteristic of most complex systems:

As with chess, complex systems typically exhibit recurring patterns that offer similar possibilities for ‘steering’.

All CAS agents, whatever their particularities, have three levels of activity: 1. Performance (moment-by-moment capabilities) 2. Credit-assignment (rating the usefulness of available capabilities) 3. Rule-discovery (generating new capabilities).

The difficulty presented by diversity is further compounded by the conditional nature of agent actions—the actions of a typical agent are conditionally dependent upon what other agents are doing.

all well-studied CAS exhibit lever points, points where a small directed action causes large predictable changes in aggregate behaviour, as when a vaccine produces long-term changes in an immune system.

Credit assignment.As an agent accumulates experience, it will find that some of its rules are rarely, or never, useful. If a frog flees from all moving objects it will rarely eat or mate. In order to adapt, an agent requires a means of assigning a quantity, usually called strength, that rates the usefulness of different rules in helping the agent t

distinctive property called emergence, roughly described by the common phrase ‘the action of the whole is more than the sum of the actions of the parts’.

analysis depends upon methods for discovering and exploiting recurring patterns in generated systems.