Multiagent Systems: Local Decisions vs. Global Coherence

1. Multiagent Systems: Local Decisions vs. Global Coherence Leen-Kiat Soh, Nobel Khandaker, Adam Eck Computer Science & Engineering University of Nebraska Lincoln, NE 68588-0115 lksoh@cse.unl.edu http://www.cse.unl.edu/agents November 25, 2008

2. Agents • What is an agent? • An agent is an entity that takes sensory input from its environment, makes autonomous decisions,and carries out actions that affect the environment • A thermostat is an agent • A calculator is not an agent Agent think! output actions sensory input Environment

3. Intelligent Agents • What is an intelligentagent? • An intelligent agent is one that is capable of flexibleautonomous actions in order to meet its design objectives, where flexibility means: • Reactivity: agents are able to perceive their environment, and respond in a timely fashion to changes that occur in order to satisfy their design objectives • Pro-activeness: agents are able to exhibit goal-directedbehavior by taking the initiative in order to satisfy their design objectives • Social ability: agents are capable of interacting with other agents (and possibly humans) in order to satisfy their design objectives (Wooldridge and Jennings 1995)

4. Intelligent Agents: Learning The acquisition of new knowledge and motor and cognitive skills and the incorporation of the acquired knowledge and skills in future system activities, provided that this acquisition and incorporation is conducted by the system itself and leads to an improvement in its performance. • Machine Learning in AI says • Agents that learn are intelligent • Not all agents are intelligent!

5. Agent Environment • Inaccessible vs. accessible – Incomplete vs. complete data • Deterministic vs. non-deterministic • Certainty vs. uncertainty • Episodic vs. non-episodic • Each episode is independent or not • Static vs. dynamic • Remain unchanged except by the performance of actions by the agent? • Discrete vs. continuous • “Chess game” vs. “taxi driving”

6. Why Agents? Why does a person hire an agent? • If the system-to-be-built has, during the execution of the system • Incomplete data • Uncertainty in the assessment/interaction of its environment • Inter-dependent episodes of events • No full control over the events in the environment • An “open world”, instead of a “closed world” • In other words, agents are used when you need to build a system that is adaptive to an uncertain, dynamic, and at times unexpected environment • So you can make full use of the autonomous property of an agent

7. Multiagent Systems • A multiagent system is a system where multiple agents perform a task better when working together • Interaction (communication) • Coordination • Collaboration • Example: A group of basketball players who do not observe or communicate with each other is not a team—simply a group of individual agents.

8. Why Multiagent Systems? • Distributed control, databases, knowledge bases, experience, expertise, execution, planning, and views of environment • Scalability, flexibility, autonomy • Distributed control, proprietary concerns, security levels, communities • Efficiency, flexibility, autonomy From the Solution point of view From the Logistics point of view

9. Local Decisions vs. Global Coherence • Agents making local decisions have high autonomy • Less reliant on other agents • No explicit global control • May lead to unexpected, “chaotic” results due to lack of coordination • A multiagent system should strive for global coherence • How well a system behave as a unit

10. Local Decisions vs. Global Coherence High Coherence DESIRABLE NOT DESIRABLE Low Coherence High Autonomy Low Autonomy

11. Multiagent Simulation Example - I • Project – Multiagent System for Mining the Asteroids • Simulated 2D space with asteroids containing ores • Scout agents search and Miner agents extract deposit • Local Decision • Limited Time and resource (scouts, miners, etc.) • How to explore the space? • How to assign miners to asteroids? • Global Coherence • Maximize average value per cargo unit

12. Multiagent Simulation Example - II • Project – Multiagent System Simulating Immune System of an Organism • Pathogens eat Red Blood Cells and Multiply, White Blood Cells Kill Pathogens • System health depends on number of Pathogens • Local Decision • Pathogens: eat the nearby red blood cells • White Blood Cells: Destroy the nearby Pathogen and Call for Help • Global Coherence • System Health

13. Multiagent Simulation Example - III • Project – Multiagent System Simulating an Inferno • 2D Space with Flammable Objects and Firefighters • Local Decision • Fire Burns the Nearby Objects • Firefighters Put Out Fire and Help Other Firefighters • Global Coherence • Put Out All Fire • Maximize the Health of the Firefighters

14. Multiagent Simulation Example - IV • Project – Multiagent System Simulating Adversarial Search • 2D Maze Containing Diplomats, Terrorists, and Allies • Terrorist and Allies Search a Maze and Try to Capture Diplomats • Local Decision • Terrorists Share a Partial Map of the Maze • Allies Share Whole Map of the Maze • Global Coherence • The Number of Diplomats Rescued By Allies

15. Multiagent Simulation Example - V • Project – Collaborative Behavior in an Online Learning Environment • One teacher who assigns A collaborative learning activities • Sstudents who can learn from one another or by themselves during an activity, and • Sstudent agents, each assigned exclusively to a particular student to make decisions to improve their student’s learning • Local Decision • Choose learning activities for students • Voting for permanent groups between students • Global Coherence • Average student knowledge converges to high levels • Long lasting student learning groups

16. Local Decisions vs. Global Coherence High Coherence INFERNO ASTEROIDS PATHOGENS TERRORISTS ALLIES STUDENT AGENTS DESIRABLE NOT DESIRABLE Low Coherence High Autonomy Low Autonomy