Emergent Mind

Fundamental Components of Deep Learning: A category-theoretic approach

(2403.13001)
Published Mar 13, 2024 in cs.LG , cs.AI , and math.CT

Abstract

Deep learning, despite its remarkable achievements, is still a young field. Like the early stages of many scientific disciplines, it is marked by the discovery of new phenomena, ad-hoc design decisions, and the lack of a uniform and compositional mathematical foundation. From the intricacies of the implementation of backpropagation, through a growing zoo of neural network architectures, to the new and poorly understood phenomena such as double descent, scaling laws or in-context learning, there are few unifying principles in deep learning. This thesis develops a novel mathematical foundation for deep learning based on the language of category theory. We develop a new framework that is a) end-to-end, b) unform, and c) not merely descriptive, but prescriptive, meaning it is amenable to direct implementation in programming languages with sufficient features. We also systematise many existing approaches, placing many existing constructions and concepts from the literature under the same umbrella. In Part I we identify and model two main properties of deep learning systems parametricity and bidirectionality by we expand on the previously defined construction of actegories and Para to study the former, and define weighted optics to study the latter. Combining them yields parametric weighted optics, a categorical model of artificial neural networks, and more. Part II justifies the abstractions from Part I, applying them to model backpropagation, architectures, and supervised learning. We provide a lens-theoretic axiomatisation of differentiation, covering not just smooth spaces, but discrete settings of boolean circuits as well. We survey existing, and develop new categorical models of neural network architectures. We formalise the notion of optimisers and lastly, combine all the existing concepts together, providing a uniform and compositional framework for supervised learning.

Overview

  • Bruno Gavcanović's PhD thesis introduces a category-theoretic mathematical foundation to unify and model the diverse phenomena in deep learning.

  • The thesis presents a novel framework, integrating parametrization and bidirectionality, which can describe deep learning systems consistently and could be implemented in future programming languages.

  • Significant contributions include the Para construction for modeling parametric morphisms and advancements in understanding bidirectionality through monoidal actegories and weighted optics.

  • Gavcanović's work aims to provide a unified language for neural network architectures, laying a foundation for future theoretical and practical developments in AI.

Exploring the Foundations of Deep Learning through Category Theory: Insights from Gavcanović's PhD Thesis

Introduction to Category-Theoretic Approach in Deep Learning

The PhD thesis by Bruno Gavcanović at the University of Strathclyde provides an innovative mathematical foundation for the study of deep learning systems through the lens of category theory. This formalism seeks to unify the diverse architectures and phenomena observed in deep learning under a comprehensive theoretical framework. By identifying and modeling the bidirectional and parametric nature of artificial neural networks, Gavcanović advances our understanding beyond current ad-hoc methods, proposing a structured, categorical model inclusive of existing deep learning concepts and offering a new perspective for future research.

Key Contributions

Gavcanović's work integrates two main properties of deep learning systems—parametrization and bidirectionality—into a coherent category-theoretic model. This model encompasses a broad range of processes found in machine learning, including but not limited to Bayesian updating and game theory. Significant contributions of the thesis include:

  • Development of a New Mathematical Framework: By employing category theory, Gavcanović introduces a novel end-to-end framework that not only describes deep learning systems uniformly but also predicates the implementation of these systems in programming languages that support the required features.
  • The Para Construction: A pivotal concept introduced is the Para construction, which rigorously models parametric morphisms within a categorical context, thereby offering a systematic approach to understand reparameterization and the composition of neural networks.
  • Advancement of Category Theory in Deep Learning: Through meticulous definition and analysis of monoidal actegories, weighted optics, and the coPara construction, Gavcanović provides a foundation for exploring bidirectionality in deep learning, encompassing a wide range of phenomena from optimization to information flow within neural architectures.
  • Operational Insights and Specifications for AI Systems: The thesis explore the operational aspects of the defined category-theoretical models, presenting implications for practical implementation and speculation on future AI developments based on this formalism.

Theoretical and Practical Implications

Gavcanović's thesis presents several theoretical advancements that have immediate practical implications, such as:

  • Unified Language for Deep Learning Architecture: Offering a unifying language for the fragmented landscape of neural network architectures, this work facilitates cross-disciplinary research and innovation within the field.
  • Foundation for Future Theoretical Developments: By establishing a rigorous mathematical basis for deep learning, this thesis sets the stage for future theoretical explorations, potentially leading to the discovery of new learning algorithms and architectures.
  • Direct Implementation Framework: The prescriptive nature of the framework has the potential to influence the development of deep learning frameworks, making them more robust and understandable.

Future Directions in AI and Machine Learning Research

The formalism introduced by Gavcanović opens numerous avenues for future research, including but not limited to:

  • Exploration of Category Theory in Other Domains of AI: Extending the categorical approach to other areas of AI, such as reinforcement learning and unsupervised learning, could uncover new insights and unify disparate methodologies.
  • Development of New Neural Network Architectures: The categorical model could lead to the design of novel neural network architectures that are inherently more interpretable and efficient.
  • Advancements in Programming Languages: There is potential for the development of programming languages or extensions that natively support the categorical constructs introduced, directly influencing the implementation of deep learning models.

Concluding Remarks

Gavcanović's work marks a significant step towards a deeper, theory-informed understanding of deep learning systems. By leveraging the powerful abstractions of category theory, this thesis not only clarifies the underlying mathematics of current deep learning phenomena but also paves the way for future advancements in artificial intelligence research.

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