Agent Policy

A key characteristic is whether the policy changes over time.

• Stationary Policy: The mapping π does not change over the course of an episode or the agent's lifetime. It is a fixed strategy.
• Non-Stationary Policy: The mapping π evolves, typically as a result of agent learning. In reinforcement learning, the policy is updated iteratively to maximize cumulative reward, transitioning from exploration to exploitation.

This distinction is central to the difference between a pre-programmed agent and a learning agent. Most advanced AI agents employ non-stationary policies.

In reinforcement learning, the relationship between the policy being evaluated/improved and the policy used to generate behavior is critical.

• On-Policy Methods: The agent learns the value of and improves the same policy it is using to make decisions. Examples include SARSA and Actor-Critic with specific updates. The policy is typically soft (e.g., ε-greedy) to ensure exploration.
• Off-Policy Methods: The agent learns the value of an optimal policy while following a different behavior policy for exploration. This allows learning from historical data or demonstrations. Q-Learning is the classic example, where it learns the optimal Q-function regardless of the action taken.

This characteristic dictates data efficiency and the ability to learn from external datasets.

A policy is designed to optimize a specific objective function, which formally defines the agent's goal.

• Reinforcement Learning: Maximizes the expected cumulative reward. The objective is J(π) = E[Σ γ^t * r_t], where γ is a discount factor.
• Imitation Learning: Minimizes the divergence between the agent's action distribution and that of an expert demonstrator.
• Safe RL: Maximizes reward subject to constraints (e.g., never enter a hazardous state).
• Multi-Objective RL: Balances competing objectives via a vectorized reward or constrained optimization.

The policy's architecture and update rule are directly derived from this formal objective.

For complex tasks, policies are often structured hierarchically or composed of modules.

• Hierarchical Policies: A high-level manager policy selects sub-goals or temporally extended actions (options), which are executed by lower-level worker policies. This abstracts away detail and improves learning efficiency.
• Modular Policies: Different policy modules are responsible for different skills or contexts, with a gating or selection mechanism choosing which module to activate. This facilitates transfer learning and compositionality.

This structure is essential in multi-agent system orchestration, where an orchestrator agent's policy may invoke and coordinate the policies of specialized subordinate agents.

Agent architecture defines the internal structure and information flow of an agent, of which the policy is one component. Common architectures include:

• Reactive: Simple condition-action rules (direct policy).
• Deliberative (BDI): Uses a Belief-Desire-Intention model, where the policy operates on beliefs and goals to form intentions (plans).
• Hybrid: Combines reactive layers for speed with deliberative layers for complex planning. The architecture determines how perception is processed into state for the policy and how the policy's output actions are executed.

A utility function is a mathematical representation of an agent's preferences, often used to derive or evaluate a policy. In rational decision theory, an optimal policy is one that maximizes expected utility. Key relationships:

• Planning: In model-based settings, an agent uses its utility function to evaluate potential future states and choose the action sequence (plan) with the highest expected utility.
• Reinforcement Learning: The reward signal is a proxy for utility; the RL policy is learned to maximize the sum of future rewards.
• Multi-Objective: Complex agents may have a vector of utility functions, requiring the policy to balance trade-offs.

In a multi-agent system, an orchestration engine is a supervisory component that can manage, configure, or even dynamically select the policies of subordinate agents. Its functions include:

• Workflow Management: Dictating the sequence in which agents (and their policies) are invoked.
• Policy Injection: Providing context-specific rules or constraints to an agent at runtime.
• Conflict Resolution: Intervening when policies of different agents lead to competing actions for shared resources. The orchestrator operates at a higher level than any single agent's policy.

Agent learning is the process by which an agent's policy is improved or adapted over time. This distinguishes a static, pre-programmed policy from a dynamic, self-improving one. Primary paradigms include:

• Reinforcement Learning: Policy is updated based on rewards/punishments from the environment.
• Imitation Learning: Policy is learned by observing demonstrations from an expert.
• Meta-Learning: The agent learns a policy that is quick to adapt (learn) in new situations. Learning transforms the policy from a fixed function into an evolving component of the agent.