A multi-agent system (MAS) is a system composed of multiple interacting intelligent agents within an environment. Multi-agent systems can be used to solve problems that are difficult or impossible for an individual agent or a monolithic system to solve. Intelligence may include some methodic, functional, procedural or algorithmic search, find and processingapproach.
Multi-agent systems consist of agents and their environment. Typically multi-agent systems research refers to software agents. However, the agents in a multi-agent system could equally well be robots, humans or human teams. A multi-agent system may contain combined human-agent teams.
Agents can be divided into different types:
- Very simple like: passive agents or agent without goals (like obstacle, apple or key in any simple simulation)
- Active agents with simple goals (like birds in flocking, or wolf-sheep in prey-predator model)
- Or very complex agents (like cognitive agent, which has a lot of complex calculations)
Environment also can be divided into:
- Virtual Environment
- Discrete Environment
- Continues Environment
Agent environments can be organized according to various properties like: accessibility (depending on if it is possible to gather complete information about the environment), determinism (if an action performed in the environment causes a definite effect), dynamics (how many entities influence the environment in the moment), discreteness (whether the number of possible actions in the environment is finite), episodicity (whether agent actions in certain time periods influence other periods), and dimensionality (whether spatial characteristics are important factors of the environment and the agent considers space in its decision making).
The agents in a multi-agent system have several important characteristics:
- Autonomy: the agents are at least partially autonomous
- Local views: no agent has a full global view of the system, or the system is too complex for an agent to make practical use of such knowledge
- Decentralization: there is no designated controlling agent (or the system is effectively reduced to a monolithic system)
Self organization and self steering
Multi-agent systems can manifest self-organization as well as self-steering and other control paradigms and related complex behaviors even when the individual strategies of all their agents are simple.
When agents can share knowledge using any agreed language, within the constraints of the system’s communication protocol, the approach may lead to a common improvement. Example languages are Knowledge Query Manipulation Language (KQML) or FIPA’s Agent Communication Language (ACL).
Many MAS systems are implemented in computer simulations, stepping the system through discrete “time steps”. The MAS components communicate typically using a weighted request matrix, e.g.
Speed-VERY_IMPORTANT: min=45 mph, Path length-MEDIUM_IMPORTANCE: max=60 expectedMax=40, Max-Weight-UNIMPORTANT Contract Priority-REGULAR
and a weighted response matrix, e.g.
Speed-min:50 but only if weather sunny, Path length:25 for sunny / 46 for rainy Contract Priority-REGULAR note - ambulance will override this priority and you'll have to wait
A challenge-response-contract scheme is common in MAS systems, where
First a "Who can?" question is distributed. Only the relevant components respond: "I can, at this price". Finally, a contract is set up, usually in several more short communication steps between sides,
also considering other components, evolving “contracts”, and the restriction sets of the component algorithms.
Another paradigm commonly used with MAS systems is the pheromone, where components “leave” information for other components “next in line” or “in the vicinity”. These “pheromones” may “evaporate” with time, that is their values may decrease (or increase) with time.
MAS systems, also referred to as “self-organized systems”, tend to find the best solution for their problems “without intervention”. There is high similarity here to physical phenomena, such as energy minimizing, where physical objects tend to reach the lowest energy possible, within the physical constrained world. For example: many of the cars entering a metropolis in the morning, will be available for leaving that same metropolis in the evening.
The main feature which is achieved when developing multi-agent systems, if they work, is flexibility, since a multi-agent system can be added to, modified and reconstructed, without the need for detailed rewriting of the application. These systems also tend to be rapidly self-recovering and failure proof, usually due to the heavy redundancy of components and the self managed features, referred to, above.
The study of multi-agent systems
The study of multi-agent systems is “concerned with the development and analysis of sophisticated AI problem-solving and control architectures for both single-agent and multiple-agent systems.” Topics of research in MAS include:
- agent-oriented software engineering
- beliefs, desires, and intentions (BDI)
- cooperation and coordination
- distributed problem solving
- multi-agent learning
- scientific communities
- dependability and fault-tolerance
- robotics 
While ad hoc multi-agent systems are often created from scratch by researchers and developers, some frameworks have arisen that implement common standards (such as the FIPA agent system platforms and communication languages). These frameworks save developers time and also aid in the standardization of MAS development. One such developmental framework for robotics is given in 
Applications in the real world
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Multi-agent systems are applied in the real world to graphical applications such as computer games. Agent systems have been used in films. They are also used for coordinated defence systems. Other applications include transportation, logistics, graphics, GIS as well as in many other fields. It is widely being advocated for use in networking and mobile technologies, to achieve automatic and dynamic load balancing, high scalability, and self-healing networks.
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- Random Agent-Based Simulations by Borys Biletskyy – Random agent-base simulations for multi-robot system and Belousov-Zhabotinsky reaction. Java applets available.
- JaCaMo MAS Platform – An open-source platform for Multi-Agent Systems based on Jason, CArtAgO, and Moise.
- Janus multiagent Platform – Holonic multiagent execution platform (free for non-commercial use).
- HarTech Technologies – HarTech Technologies developed a dedicated Distributed Multi Agent System Framework used in both simulation and large scale command and control system. This unique framework called the Generic Blackboard (GBB) provides a development framework for such systems which is domain independent. Distributed Multi Agent Framework.