Search

We introduce an ensemble of classifiers-based approach for incremental learning of concept drift, characterized by nonstationary environments (NSEs), where the underlying data distributions change over time. The proposed algorithm, named Learn^++.NSE, learns from consecutive batches of data without making any assumptions on the nature or rate of drift; it can learn from such environments that experience constant or variable rate of drift, addition or deletion of concept classes, as well as cyclical drift. The algorithm learns incrementally, as other members of the Learn^++ family of algorithms, that is, without requiring access to previously seen data. Learn^++.NSE trains one new classifier for each batch of data it receives, and combines these classifiers using a dynamically weighted majority voting. The novelty of the approach is in determining the voting weights, based on each classifier's time-adjusted accuracy on current and past environments. This approach allows the algorithm to recognize, and act accordingly, to the changes in underlying data distributions, as well as to a possible reoccurrence of an earlier distribution. We evaluate the algorithm on several synthetic datasets designed to simulate a variety of nonstationary environments, as well as a real-world weather prediction dataset. Comparisons with several other approaches are also included. Results indicate that Learn^++.NSE can track the changing environments very closely, regardless of the type of concept drift. To allow future use, comparison and benchmarking by interested researchers, we also release our data used in this paper. [ABSTRACT FROM AUTHOR]

This study introduces a method to enable a robot to learn how to perform new tasks through human demonstration and independent practice. The proposed process consists of two interconnected phases; in the first phase, state-action data are obtained from human demonstrations, and an aggregated state space is learned in terms of a decision tree that groups similar states together through reinforcement learning. Without the postprocess of trimming, in tree induction, the tree encodes a control policy that can be used to control the robot by means of repeatedly improving itself. Once a variety of behaviors is learned, more elaborate behaviors can be generated by selectively organizing several behaviors using another Q-learning algorithm. The composed outputs of the organized basic behaviors on the motor level are weighted using the policy learned through Q-learning. This approach uses three diverse Q-learning algorithms to learn complex behaviors. The experimental results show that the learned complicated behaviors, organized according to individual basic behaviors by the three Q-learning algorithms on different levels, can function more adaptively in a dynamic environment. [ABSTRACT FROM PUBLISHER]