Specialization in Hierarchical Learning Systems

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Specialization in Hierarchical Learning Systems A Unified Information-theoretic Approach for Supervised, Unsupervised and Reinforcement Learning Heinke Hihn1

· Daniel A. Braun1

Accepted: 5 September 2020 © The Author(s) 2020

Abstract Joining multiple decision-makers together is a powerful way to obtain more sophisticated decision-making systems, but requires to address the questions of division of labor and specialization. We investigate in how far information constraints in hierarchies of experts not only provide a principled method for regularization but also to enforce specialization. In particular, we devise an information-theoretically motivated on-line learning rule that allows partitioning of the problem space into multiple sub-problems that can be solved by the individual experts. We demonstrate two different ways to apply our method: (i) partitioning problems based on individual data samples and (ii) based on sets of data samples representing tasks. Approach (i) equips the system with the ability to solve complex decision-making problems by finding an optimal combination of local expert decision-makers. Approach (ii) leads to decision-makers specialized in solving families of tasks, which equips the system with the ability to solve meta-learning problems. We show the broad applicability of our approach on a range of problems including classification, regression, density estimation, and reinforcement learning problems, both in the standard machine learning setup and in a meta-learning setting. Keywords Meta-learning · Information theory · Bounded rationality

1 Introduction Intelligent agents are often conceptualized as decision-makers that learn probabilistic models of their environment and optimize utilities or disutilities like cost or loss functions [91]. In the general case we can think of a utility function as a black-box oracle that provides a numerical score that rates any proposed solution to a supervised, unsupervised or reinforcement learning problem. In context of decision-making, naïvely enumerating all possibilities

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Heinke Hihn [email protected] Daniel A. Braun [email protected]

1

Institute for Neural Information Processing, Ulm University, Ulm, Germany

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H. Hihn, D. A. Braun

and searching for an optimal solution is usually prohibitively expensive. Instead, intelligent agents must invest their limited resources in such a way that they achieve an optimal trade-off between expected utility and resource costs in order to enable efficient learning and acting. This trade-off is the central issue in the fields of bounded or computational rationality with repercussions across other disciplines including economics, psychology, neuroscience and artificial intelligence [3,16,23,24,26,35,55,66,78]. The information-theoretic approach to bounded rationality is a particular instance of bounded rationality where the resource limitations are modeled by information constraints [18,28,54,59,63,64,73,85,92] closely related to Jaynes’ maximum entropy or minimum relative entropy principle