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Towards Informed Exploration for Deep Reinforcement Learning
In this thesis, we discuss various techniques for improving exploration for deep reinforcement learning. We begin with a brief review of reinforcement learning (RL) and the fundamental v.s. exploitation trade-off. Then we review how deep RL has improved upon classical and summarize six categories of the latest exploration methods for deep RL, in the order increasing usage of prior information. We then explore representative works in three categories discuss their strengths and weaknesses. The first category, represented by Soft Q-learning, uses regularization to encourage exploration. The second category, represented by count-based via hashing, maps states to hash codes for counting and assigns higher exploration to less-encountered states. The third category utilizes hierarchy and is represented by modular architecture for RL agents to play StarCraft II. Finally, we conclude that exploration by prior knowledge is a promising research direction and suggest topics of potentially impact
Cross-Entropy Estimators for Sequential Experiment Design with Reinforcement Learning
Reinforcement learning can effectively learn amortised design policies for
designing sequences of experiments. However, current methods rely on
contrastive estimators of expected information gain, which require an
exponential number of contrastive samples to achieve an unbiased estimation. We
propose an alternative lower bound estimator, based on the cross-entropy of the
joint model distribution and a flexible proposal distribution. This proposal
distribution approximates the true posterior of the model parameters given the
experimental history and the design policy. Our estimator requires no
contrastive samples, can achieve more accurate estimates of high information
gains, allows learning of superior design policies, and is compatible with
implicit probabilistic models. We assess our algorithm's performance in various
tasks, including continuous and discrete designs and explicit and implicit
likelihoods
Closed-Loop Learning of Visual Control Policies
In this paper we present a general, flexible framework for learning mappings
from images to actions by interacting with the environment. The basic idea is
to introduce a feature-based image classifier in front of a reinforcement
learning algorithm. The classifier partitions the visual space according to the
presence or absence of few highly informative local descriptors that are
incrementally selected in a sequence of attempts to remove perceptual aliasing.
We also address the problem of fighting overfitting in such a greedy algorithm.
Finally, we show how high-level visual features can be generated when the power
of local descriptors is insufficient for completely disambiguating the aliased
states. This is done by building a hierarchy of composite features that consist
of recursive spatial combinations of visual features. We demonstrate the
efficacy of our algorithms by solving three visual navigation tasks and a
visual version of the classical Car on the Hill control problem
Constructing Parsimonious Analytic Models for Dynamic Systems via Symbolic Regression
Developing mathematical models of dynamic systems is central to many
disciplines of engineering and science. Models facilitate simulations, analysis
of the system's behavior, decision making and design of automatic control
algorithms. Even inherently model-free control techniques such as reinforcement
learning (RL) have been shown to benefit from the use of models, typically
learned online. Any model construction method must address the tradeoff between
the accuracy of the model and its complexity, which is difficult to strike. In
this paper, we propose to employ symbolic regression (SR) to construct
parsimonious process models described by analytic equations. We have equipped
our method with two different state-of-the-art SR algorithms which
automatically search for equations that fit the measured data: Single Node
Genetic Programming (SNGP) and Multi-Gene Genetic Programming (MGGP). In
addition to the standard problem formulation in the state-space domain, we show
how the method can also be applied to input-output models of the NARX
(nonlinear autoregressive with exogenous input) type. We present the approach
on three simulated examples with up to 14-dimensional state space: an inverted
pendulum, a mobile robot, and a bipedal walking robot. A comparison with deep
neural networks and local linear regression shows that SR in most cases
outperforms these commonly used alternative methods. We demonstrate on a real
pendulum system that the analytic model found enables a RL controller to
successfully perform the swing-up task, based on a model constructed from only
100 data samples
Indirect Methods for Robot Skill Learning
Robot learning algorithms are appealing alternatives for acquiring rational robotic behaviors from data collected during the execution of tasks. Furthermore, most robot learning techniques are stated as isolated stages and focused on directly obtaining rational policies as a result of optimizing only performance measures of single tasks. However, formulating robotic skill acquisition processes in such a way have some disadvantages. For example, if the same skill has to be learned by different robots, independent learning processes should be carried out for acquiring exclusive policies for each robot. Similarly, if a robot has to learn diverse skills, the robot should acquire the policy for each task in separate learning processes, in a sequential order and commonly starting from scratch. In the same way, formulating the learning process in terms of only the performance measure, makes robots to unintentionally avoid situations that should not be repeated, but without any mechanism that captures the necessity of not repeating those wrong behaviors. In contrast, humans and other animals exploit their experience not only for improving the performance of the task they are currently executing, but for constructing indirectly multiple models to help them with that particular task and to generalize to new problems. Accordingly, the models and algorithms proposed in this thesis seek to be more data efficient and extract more information from the interaction data that is collected either from expert\u2019s demonstrations or the robot\u2019s own experience. The first approach encodes robotic skills with shared latent variable models, obtaining latent representations that can be transferred from one robot to others, therefore avoiding to learn the same task from scratch. The second approach learns complex rational policies by representing them as hierarchical models that can perform multiple concurrent tasks, and whose components are learned in the same learning process, instead of separate processes. Finally, the third approach uses the interaction data for learning two alternative and antagonistic policies that capture what to and not to do, and which influence the learning process in addition to the performance measure defined for the task
Leveraging Demonstrations with Latent Space Priors
Demonstrations provide insight into relevant state or action space regions,
bearing great potential to boost the efficiency and practicality of
reinforcement learning agents. In this work, we propose to leverage
demonstration datasets by combining skill learning and sequence modeling.
Starting with a learned joint latent space, we separately train a generative
model of demonstration sequences and an accompanying low-level policy. The
sequence model forms a latent space prior over plausible demonstration
behaviors to accelerate learning of high-level policies. We show how to acquire
such priors from state-only motion capture demonstrations and explore several
methods for integrating them into policy learning on transfer tasks. Our
experimental results confirm that latent space priors provide significant gains
in learning speed and final performance. We benchmark our approach on a set of
challenging sparse-reward environments with a complex, simulated humanoid, and
on offline RL benchmarks for navigation and object manipulation. Videos, source
code and pre-trained models are available at the corresponding project website
at https://facebookresearch.github.io/latent-space-priors .Comment: Published in Transactions on Machine Learning Research (03/2023
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