First of all, don't really understand what you want to ask, RL is just like any ANN but in addition, you use penalties. This is one of the articles I googled in a rush: https://arxiv.org/html/2401.07553v1
Take chess as an example. One constrain might ensure penalty system for bad moves or reward for good moves. But you might need to forbid some moves, and that can also be done with various restrictions. It is up to you how it will be programmed into the AI. You can limit inputs, use loss or restrict output, just let your creativity shine.
Safe Reinforcement Learning (Safe RL) focuses on learning policies that not only maximize the expected return but also ensure the safety of the agent throughout the learning process and after deployment. Safety in RL can pertain to physical safety, adherence to ethical guidelines, compliance with rules, or avoidance of catastrophic failures. The incorporation of safety constraints into the RL framework is crucial to achieve these objectives.
Why Use Discount Accumulation Form for Constraints?
The use of a discount accumulation form for constraints in Safe RL is inspired by the discounted return formulation commonly used in standard RL to compute the future value of rewards. Just as the discounted sum of rewards provides a single scalar value representing the total expected return of a policy over time, a similar formulation for constraints allows for the incorporation of future safety considerations into the decision-making process.
The discount accumulation form for constraints typically involves the expected cumulative cost or risk, discounted over time, not exceeding a certain threshold. This formulation ensures that not only immediate safety violations are considered but also their potential long-term implications. The discount factor, similar to its role in optimizing rewards, balances the importance of immediate versus future safety outcomes.
Other Forms of Constraints
Aside from discount accumulation form, Safe RL can involve various other types of constraints, including but not limited to:
State Constraints: Restrictions on entering certain states that are deemed unsafe or undesirable. These can be hard constraints, where entering a specific state is forbidden, or soft constraints, where entering a state incurs a significant penalty.
Action Constraints: Limitations on the actions that the agent can take in certain states to prevent unsafe behavior. This can involve restricting the action space based on the current state or the history of states and actions.
Risk Constraints: Constraints based on measures of risk, such as the variance of returns or the probability of catastrophic failure. These constraints aim to limit the uncertainty and potential negative outcomes associated with certain policies.
Reward Shaping: Although not a constraint in the traditional sense, reward shaping can indirectly enforce safety by penalizing unsafe actions or rewarding safe behavior, guiding the agent towards safer policies.
Model Constraints: In model-based RL, constraints can be applied to the model of the environment itself, such as ensuring that the model does not predict unsafe outcomes.
Performance Constraints: Ensuring that the safety mechanisms do not degrade the performance of the RL agent below a certain acceptable threshold.
The choice of constraints and their formulation depends on the specific safety requirements of the application, the characteristics of the environment, and the desired balance between safety and performance. In all cases, the objective is to develop RL policies that achieve their goals while minimizing risk and ensuring safety.