MOO-MDP: An Object-Oriented Representation for Cooperative Multiagent Reinforcement Learning

Differential Advising in Multiagent Reinforcement Learning

Agent advising is one of the main approaches to improve agent learning performance by enabling agents to share advice. Existing advising methods have a common limitation that an adviser agent can offer advice to an advisee agent only if the advice is created in the same state as the advisee's state. However, in complex environments, it is a very strong requirement that two states are the same, because a state may consist of multiple dimensions and two states being the same means that all these dimensions in the two states are correspondingly identical. Therefore, this requirement may limit the applicability of existing advising methods to complex environments. In this article, inspired by the differential privacy scheme, we propose a differential advising method that relaxes this requirement by enabling agents to use advice in a state even if the advice is created in a slightly different state. Compared with the existing methods, agents using the proposed method have more opportunity to take advice from others. This article is the first to adopt the concept of differential privacy on advising to improve agent learning performance instead of addressing security issues. The experimental results demonstrate that the proposed method is more efficient in complex environments than the existing methods.

Model Learning and Knowledge Sharing for Cooperative Multiagent Systems in Stochastic Environment

An imposing task for a reinforcement learning agent in an uncertain environment is to expeditiously learn a policy or a sequence of actions, with which it can achieve the desired goal. In this article, we present an incremental model learning scheme to reconstruct the model of a stochastic environment. In the proposed learning scheme, we introduce a clustering algorithm to assimilate the model information and estimate the probability for each state transition. In addition, utilizing the reconstructed model, we present an experience replay strategy to create virtual interactive experiences by incorporating a balance between exploration and exploitation, which greatly accelerates learning and enables planning. Furthermore, we extend the proposed learning scheme for a multiagent framework to decrease the effort required for exploration and to reduce the learning time in a large environment. In this multiagent framework, we introduce a knowledge-sharing algorithm to share the reconstructed model information among the different agents, as needed, and develop a computationally efficient knowledge fusing mechanism to fuse the knowledge acquired using the agents' own experience with the knowledge received from its teammates. Finally, the simulation results with comparative analysis are provided to demonstrate the efficacy of the proposed methods in the complex learning tasks.

S$$^{2}$$ES: a stationary and scalable knowledge transfer approach for multiagent reinforcement learning

Knowledge transfer is widely adopted in accelerating multiagent reinforcement learning (MARL). To accelerate the learning speed of MARL for learning-from scratch agents, in this paper, we propose a Stationary and Scalable knowledge transfer approach based on Experience Sharing (S$$^{2}$$ 2 ES). The mainframe of our approach is structured into three components: what kind of experience, how to learn, and when to transfer. Specifically, we first design an augmented form of experience. By sharing (i.e., transmitting) the experience from one agent to its peers, the learning speed can be effectively enhanced with guaranteed scalability. A synchronized learning pattern is then adopted, which reduces the nonstationarity brought by experience replay, and at the same time retains data efficiency. Moreover, to avoid redundant transfer when the agents’ policies have converged, we further design two trigger conditions, one is modified Q value-based and another is normalized Shannon entropy-based, to determine when to conduct experience sharing. Empirical studies indicate that the proposed approach outperforms the other knowledge transfer methods in efficacy, efficiency, and scalability. We also provide ablation experiments to demonstrate the necessity of the key ingredients.

Multiagent Adversarial Collaborative Learning via Mean-Field Theory

Multiagent reinforcement learning (MARL) has recently attracted considerable attention from both academics and practitioners. Core issues, e.g., the curse of dimensionality due to the exponential growth of agent interactions and nonstationary environments due to simultaneous learning, hinder the large-scale proliferation of MARL. These problems deteriorate with an increased number of agents. To address these challenges, we propose an adversarial collaborative learning method in a mixed cooperative-competitive environment, exploiting friend-or-foe Q-learning and mean-field theory. We first treat neighbors of agent i as two coalitions ( i 's friend and opponent coalition, respectively), and convert the Markov game into a two-player zero-sum game with an extended action set. By exploiting mean-field theory, this new game simplifies the interactions as those between a single agent and the mean effects of friends and opponents. A neural network is employed to learn the optimal mean effects of these two coalitions, which are trained via adversarial max and min steps. In the max step, with fixed policies of opponents, we optimize the friends' mean action to maximize their rewards. In the min step, the mean action of opponents is trained to minimize the friends' rewards when the policies of friends are frozen. These two steps are proved to converge to a Nash equilibrium. Then, another neural network is applied to learn the best response of each agent toward the mean effects. Finally, the adversarial max and min steps can jointly optimize the two networks. Experiments on two platforms demonstrate the learning effectiveness and strength of our approach, especially with many agents.