Representation learning and option discovery are two of the biggest challenges in reinforcement learning (RL). Proto-RL is a well known approach for representation learning in MDPs. The representations learned with this framework are called proto-value functions (PVFs). In this paper we address the option discovery problem by showing how PVFs implicitly define options. We do it by introducing eigenpurposes, intrinsic reward functions derived from the learned representations. The options discovered from eigenpurposes traverse the principal directions of the state space. They are useful for multiple tasks because they are independent of the agents' intentions. Moreover, by capturing the diffusion process of a random walk, different options act at different time scales, making them helpful for exploration strategies. We demonstrate features of eigenpurposes in traditional tabular domains as well as in Atari 2600 games.
Our algorithm can be seen as a approach, in which options are constructed before the agent observes any informative reward. These options are composed to generate the desired policy. Options discovered this way tend to be independent of an agent's intention, and are potentially useful in many different tasks @cite_12 . Such options can also be seen as being useful for exploration by allowing agents to commit to a behavior for an extended period of time @cite_0 . Among the approaches to discover options without using extrinsic rewards are the use of global or local graph centrality measures @cite_10 @cite_21 @cite_4 and clustering of states @cite_17 @cite_13 @cite_25 . Interestingly, and also use the graph Laplacian in their algorithm, but to identify bottleneck states.
@cite_13 @cite_4 @cite_21 @cite_0 @cite_10 @cite_25 @cite_12 @cite_17
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The bottleneck concept in reinforcement learning has played a prominent role in automatically finding temporal abstractions from experience. Lacking significant theory, it has however been regarded by some as being merely a trick. This thesis attempts to gain better intuition about this approach using spectral graph theory. A connection to the theory of Nearly Decomposable Markov Chains is also drawn and shows great promise. An options discovery algorithm is proposed and is the first of its kind to be applicable in continuous state spaces. As opposed to other similar approaches, this one has running time O(mn2) rather than O(n3) making it suitable to much larger domains than the typical grid worlds. We introduce a skill discovery method for reinforcement learning in continuous domains that constructs chains of skills leading to an end-of-task reward. We demonstrate experimentally that it creates appropriate skills and achieves performance benefits in a challenging continuous domain. We present a new subgoal-based method for automatically creating useful skills in reinforcement learning. Our method identifies subgoals by partitioning local state transition graphs---those that are constructed using only the most recent experiences of the agent. The local scope of our subgoal discovery method allows it to successfully identify the type of subgoals we seek---states that lie between two densely-connected regions of the state space while producing an algorithm with low computational cost. Artificial intelligence is commonly defined as the ability to achieve goals in the world. In the reinforcement learning framework, goals are encoded as reward functions that guide agent behaviour, and the sum of observed rewards provide a notion of progress. However, some domains have no such reward signal, or have a reward signal so sparse as to appear absent. Without reward feedback, agent behaviour is typically random, often dithering aimlessly and lacking intentionality. In this paper we present an algorithm capable of learning purposeful behaviour in the absence of rewards. The algorithm proceeds by constructing temporally extended actions (options), through the identification of purposes that are "just out of reach" of the agent's current behaviour. These purposes establish intrinsic goals for the agent to learn, ultimately resulting in a suite of behaviours that encourage the agent to visit different parts of the state space. Moreover, the approach is particularly suited for settings where rewards are very sparse, and such behaviours can help in the exploration of the environment until reward is observed. We consider a graph theoretic approach for automatic construction of options in a dynamic environment. A map of the environment is generated on-line by the learning agent, representing the topological structure of the state transitions. A clustering algorithm is then used to partition the state space to different regions. Policies for reaching the different parts of the space are separately learned and added to the model in a form of options (macro-actions). The options are used for accelerating the Q-Learning algorithm. We extend the basic algorithm and consider building a map that includes preliminary indication of the location of "interesting" regions of the state space, where the value gradient is significant and additional exploration might be beneficial. Experiments indicate significant speedups, especially in the initial learning phase.