Reinforcement Learning
Reinforcement Learning for Education
I have been studying reinforcement learning since November 2018 when I learned what is was during my time with Insight Data Science. I was an artificial intelligence fellow and I was so fascinated by this idea that you could simulate an environment and get an agent to learn an optimal policy to maximize rewards from that environment. The more I read about RL the more I noticed men were using RL to either train robots or using it to create and play video games. I thought this was such a whack idea! Robots are really cool but reinforcement learning could be used for so much more, I just didn't have any examples of how it could be done yet so I imagined one possibility for using reinforcement learning in an educational environment.
Sample-efficient AI
Since AlphaGo, AI researchers have recognized the promise of integrating reinforcement learning with search methods, which involve considering many potential next actions available to an RL agent, and simulating what their results might be before choosing one. This starts to mimic human deliberation much more closely, by explicitly introducing elements of "planning" into the RL paradigm. Yang attributes the huge performance improvements of AlphaGo, AlphaZero and MuZero to this search process. Another important distinction in RL is between model-based systems, which construct explicit models of their environments, and model-free systems, which don't. Prior to AlphaGo, just about all leading RL work was done on model-free systems (PPO and deep Q learning, for example). Model-based systems just weren't practical because the learning environment models is hard, and adds a significant layer of complexity on top of the simpler action selection task that model-free systems could focus on exclusively.
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An Experimental Design Perspective on Model-Based Reinforcement Learning
Mehta, Viraj, Paria, Biswajit, Schneider, Jeff, Ermon, Stefano, Neiswanger, Willie
In many practical applications of RL, it is expensive to observe state transitions from the environment. For example, in the problem of plasma control for nuclear fusion, computing the next state for a given state-action pair requires querying an expensive transition function which can lead to many hours of computer simulation or dollars of scientific research. Such expensive data collection prohibits application of standard RL algorithms which usually require a large number of observations to learn. In this work, we address the problem of efficiently learning a policy while making a minimal number of state-action queries to the transition function. In particular, we leverage ideas from Bayesian optimal experimental design to guide the selection of state-action queries for efficient learning. We propose an acquisition function that quantifies how much information a state-action pair would provide about the optimal solution to a Markov decision process. At each iteration, our algorithm maximizes this acquisition function, to choose the most informative state-action pair to be queried, thus yielding a data-efficient RL approach. We experiment with a variety of simulated continuous control problems and show that our approach learns an optimal policy with up to $5$ -- $1,000\times$ less data than model-based RL baselines and $10^3$ -- $10^5\times$ less data than model-free RL baselines. We also provide several ablated comparisons which point to substantial improvements arising from the principled method of obtaining data.
Zero-Shot Uncertainty-Aware Deployment of Simulation Trained Policies on Real-World Robots
Rana, Krishan, Dasagi, Vibhavari, Haviland, Jesse, Talbot, Ben, Milford, MIchael, Sünderhauf, Niko
While deep reinforcement learning (RL) agents have demonstrated incredible potential in attaining dexterous behaviours for robotics, they tend to make errors when deployed in the real world due to mismatches between the training and execution environments. In contrast, the classical robotics community have developed a range of controllers that can safely operate across most states in the real world given their explicit derivation. These controllers however lack the dexterity required for complex tasks given limitations in analytical modelling and approximations. In this paper, we propose Bayesian Controller Fusion (BCF), a novel uncertainty-aware deployment strategy that combines the strengths of deep RL policies and traditional handcrafted controllers. In this framework, we can perform zero-shot sim-to-real transfer, where our uncertainty based formulation allows the robot to reliably act within out-of-distribution states by leveraging the handcrafted controller while gaining the dexterity of the learned system otherwise. We show promising results on two real-world continuous control tasks, where BCF outperforms both the standalone policy and controller, surpassing what either can achieve independently. A supplementary video demonstrating our system is provided at https://bit.ly/bcf_deploy.
Learning Generalizable Behavior via Visual Rewrite Rules
Xie, Yiheng, Li, Mingxuan, Yu, Shangqun, Littman, Michael
Though deep reinforcement learning agents have achieved unprecedented success in recent years, their learned policies can be brittle, failing to generalize to even slight modifications of their environments or unfamiliar situations. The black-box nature of the neural network learning dynamics makes it impossible to audit trained deep agents and recover from such failures. In this paper, we propose a novel representation and learning approach to capture environment dynamics without using neural networks. It originates from the observation that, in games designed for people, the effect of an action can often be perceived in the form of local changes in consecutive visual observations. Our algorithm is designed to extract such vision-based changes and condense them into a set of action-dependent descriptive rules, which we call ''visual rewrite rules'' (VRRs). We also present preliminary results from a VRR agent that can explore, expand its rule set, and solve a game via planning with its learned VRR world model. In several classical games, our non-deep agent demonstrates superior performance, extreme sample efficiency, and robust generalization ability compared with several mainstream deep agents.
Learning Transferable Motor Skills with Hierarchical Latent Mixture Policies
Rao, Dushyant, Sadeghi, Fereshteh, Hasenclever, Leonard, Wulfmeier, Markus, Zambelli, Martina, Vezzani, Giulia, Tirumala, Dhruva, Aytar, Yusuf, Merel, Josh, Heess, Nicolas, Hadsell, Raia
For robots operating in the real world, it is desirable to learn reusable behaviours that can effectively be transferred and adapted to numerous tasks and scenarios. We propose an approach to learn abstract motor skills from data using a hierarchical mixture latent variable model. In contrast to existing work, our method exploits a three-level hierarchy of both discrete and continuous latent variables, to capture a set of high-level behaviours while allowing for variance in how they are executed. We demonstrate in manipulation domains that the method can effectively cluster offline data into distinct, executable behaviours, while retaining the flexibility of a continuous latent variable model. The resulting skills can be transferred and fine-tuned on new tasks, unseen objects, and from state to vision-based policies, yielding better sample efficiency and asymptotic performance compared to existing skill- and imitation-based methods. We further analyse how and when the skills are most beneficial: they encourage directed exploration to cover large regions of the state space relevant to the task, making them most effective in challenging sparse-reward settings.
VMAgent: Scheduling Simulator for Reinforcement Learning
Sheng, Junjie, Cai, Shengliang, Cui, Haochuan, Li, Wenhao, Hua, Yun, Jin, Bo, Zhou, Wenli, Hu, Yiqiu, Zhu, Lei, Peng, Qian, Zha, Hongyuan, Wang, Xiangfeng
A novel simulator called VMAgent is introduced to help RL researchers better explore new methods, especially for virtual machine scheduling. VMAgent is inspired by practical virtual machine (VM) scheduling tasks and provides an efficient simulation platform that can reflect the real situations of cloud computing. Three scenarios (fading, recovering, and expansion) are concluded from practical cloud computing and corresponds to many reinforcement learning challenges (high dimensional state and action spaces, high non-stationarity, and life-long demand). VMAgent provides flexible configurations for RL researchers to design their customized scheduling environments considering different problem features. From the VM scheduling perspective, VMAgent also helps to explore better learning-based scheduling solutions.
Learning multiple gaits of quadruped robot using hierarchical reinforcement learning
Kim, Yunho, Son, Bukun, Lee, Dongjun
There is a growing interest in learning a velocity command tracking controller of quadruped robot using reinforcement learning due to its robustness and scalability. However, a single policy, trained end-to-end, usually shows a single gait regardless of the command velocity. This could be a suboptimal solution considering the existence of optimal gait according to the velocity for quadruped animals. In this work, we propose a hierarchical controller for quadruped robot that could generate multiple gaits (i.e. pace, trot, bound) while tracking velocity command. Our controller is composed of two policies, each working as a central pattern generator and local feedback controller, and trained with hierarchical reinforcement learning. Experiment results show 1) the existence of optimal gait for specific velocity range 2) the efficiency of our hierarchical controller compared to a controller composed of a single policy, which usually shows a single gait. Codes are publicly available.
A Comparative Analysis of Machine Learning Techniques for IoT Intrusion Detection
Vitorino, João, Andrade, Rui, Praça, Isabel, Sousa, Orlando, Maia, Eva
The digital transformation faces tremendous security challenges. In particular, the growing number of cyber-attacks targeting Internet of Things (IoT) systems restates the need for a reliable detection of malicious network activity. This paper presents a comparative analysis of supervised, unsupervised and reinforcement learning techniques on nine malware captures of the IoT-23 dataset, considering both binary and multi-class classification scenarios. The developed models consisted of Support Vector Machine (SVM), Extreme Gradient Boosting (XGBoost), Light Gradient Boosting Machine (LightGBM), Isolation Forest (iForest), Local Outlier Factor (LOF) and a Deep Reinforcement Learning (DRL) model based on a Double Deep Q-Network (DDQN), adapted to the intrusion detection context. The most reliable performance was achieved by LightGBM. Nonetheless, iForest displayed good anomaly detection results and the DRL model demonstrated the possible benefits of employing this methodology to continuously improve the detection. Overall, the obtained results indicate that the analyzed techniques are well suited for IoT intrusion detection.