Research work

Table 1.1 compares the Cartesian approach with a systems approach. The different characteristics of the complex systems [20] present in figure 1.3 will be detailed later.

Complex systems work from the bottom up. It is the agents at the bottom of the hierarchy who make the systems work, who produce emergent phenomena through interactions between them and with their environment.

The role of the top of the hierarchy is limited to creating conditions favorable to the emergence of the desired phenomena (basin of attraction). The capacities for adaptation and innovation of an organization thus decentralized are notably greater than those of a centralized structure.

Complex systems cannot be divided, remember that entropy tells us that “the whole is more than the sum of the parts”. To study a complex system, all of its components must be considered simultaneously: agents, interactions and the environment. It is also necessary to take into account the interactions and the temporal evolution of the system.

It is necessary to bring together multidisciplinary skills that cover all facets of the system studied. This arises from holism which does not allow properties linked to different disciplines to be studied in isolation. As a reminder, Figure 1.1 presents various theories related to all complex systems.

Agents have different properties, laws, rules, behaviors and actions. Agents can however be grouped by class. Very often the specification of agents is of the order of UML diagrams in 4+1 views. The diversity of agents reinforces the properties of complex adaptive systems: emergence, innovation, self-organization.

Medium and long-term developments in complex systems are unpredictable because it is impossible to define all the variables with the precision required for a forecast. Accuracy requirements grow exponentially with the scope of forecasts.

It can be futile to try to identify the cause of a situation observed in a system because this situation is often due to multiple causes. It is impossible to identify a main cause among these multiple causes which have been the subject of a succession of amplifications and attenuations due to feedbacks.

For example, the causes of the rise or weakening of a civilization are often uncertain with controversies fueled by numerous theses. It is necessary to distinguish the accidental cause which triggered an event from all the causes which created the latent state which allowed this triggering. This accidental cause is easily identifiable and is sometimes wrongly considered as the main cause of this event.

Complex systems are subject to shifts which are sudden developments in terms of their scale and speed. For example, a collective enthusiasm, an economic crisis, a revolution, or the initial conditions. A tipping point is a state of a system where a small cause can cause a profound and abrupt change in the state of the system.

Like any chaotic system, a complex system has cycles of evolution between the different basins of attractions. A shift can be conceptualized as a jump from one basin of attraction to another. We often do not know how to identify the attractors of complex systems.

Feedback occurs when an agent receives stimuli that are influenced by the stimuli it emitted. Feedbacks generate the fundamental properties of complex systems: holism, convergence towards basins of attraction, cyclical dynamics, bifurcations, shifts, evolution, adaptation, emergence, self-organization, etc. Feedbacks can have a stabilizing effect, for example regulating supply by demand in a market, or on the contrary an amplifying effect, for example creating booms whose archetype is a speculative bubble. The adaptive capacities of complex systems are due to feedback which causes the rules of behavior of their agents to evolve based on their experiences.

Combinations of these characteristics lead to the main characteristic of all complex systems: emergence. Emergence is the creation (of a holistic view) or self-organization (of a micro view) of new characters or phenomena in the system. Emergence is necessary for adaptation, evolution, coevolution, reproduction.

This occurs in various forms:

1. an adaptation/evolution of the characteristics of agents in space and time;
2. an adaptation/evolution of behavior and rules of agents in space and time;
3. self-organization with specialization of agents;
4. self-organization with hierarchy of agents;
5. coevolution between a pair or more agents;
6. a creation of new agents by evolution and specialization of existing agents.