Abstract

We provide a rigorous mathematical formulation of Deep Learning (DL) methodologies through an in-depth analysis of the learning procedures characterizing Neural Network (NN) models within the theoretical frameworks of Stochastic Optimal Control (SOC) and Mean-Field Games (MFGs). In particular, we show how the supervised learning approach can be translated in terms of a (stochastic) mean-field optimal control problem by applying the Hamilton–Jacobi–Bellman (HJB) approach and the mean-field Pontryagin maximum principle. Our contribution sheds new light on a possible theoretical connection between mean-field problems and DL, melting heterogeneous approaches and reporting the state-of-the-art within such fields to show how the latter different perspectives can be indeed fruitfully unified.

Highlights

  • IntroductionWhen we have to analyse complex dynamics produced by the mutual interaction of a large set of indistinguishable players, an efficient approach to infer knowledge about the resulting behaviour, typical for example of a neuronal ensemble, is provided by Mean-Field Game (MFG) methods, as described in [1]

  • We provide connections between the global and local formulation of the HJB formalism via the Pontryagin Maximum Principle (PMP), exploiting the connection between Hamilton’s canonical equations (ODEs) and the Hamilton–Jacobi equations (PDEs)

  • Typical Neural Network (NN) structures are considered as the evolution of a dynamical system to rigorously state the population risk minimization problem related to Deep Learning (DL)

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Summary

Introduction

When we have to analyse complex dynamics produced by the mutual interaction of a large set of indistinguishable players, an efficient approach to infer knowledge about the resulting behaviour, typical for example of a neuronal ensemble, is provided by Mean-Field Game (MFG) methods, as described in [1]. Neural Networks (NNs) are trained through the Stochastic Gradient Descent (SGD) method It updates the trainable parameters using gradient information computed randomly via a back-propagation algorithm with the disadvantage of being slow in the first steps of training.

Wasserstein Metrics
Stochastic Optimal Control Problem
Mean-Field Games
Main Result
Neural Network as a Dynamical System
HJB Equation
Mean-Field Pontryagin Maximum Principle
Connection between the HJB Equation and the PMP
Small-Time Uniqueness
Conclusions
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