Abstract

Concentration inequalities are widely used for analyzing machine learning algorithms. However, the current concentration inequalities cannot be applied to some non-causal processes which appear for instance in Natural Language Processing (NLP). This is mainly due to the non-causal nature of such involved data, in the sense that each data point depends on other neighboring data points. In this paper, we establish a framework for modeling non-causal random fields and prove a Hoeffding-type concentration inequality. The proof of this result is based on a local approximation of the non-causal random field by a function of a finite number of i.i.d. random variables.

Highlights

  • Concentration inequalities are widely used in statistical learning

  • The current concentration inequalities cannot be applied to some non-causal processes which appear for instance in Natural Language Processing (NLP)

  • The proof of this result is based on a local approximation of the non-causal random field by a function of a finite number of i.i.d. random variables

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Summary

Introduction

Concentration inequalities are widely used in statistical learning. For example, model selection techniques rely heavily on concentration inequalities [28]. The BERT model [21] has become a staple for a very large range of NLP tasks, such as translation, part-of-speech tagging, sentiment analysis Despite their success in practical applications, it lacks a theoretical framework to analyze such non-causal models. The natural extension of Markov chains to random fields leads to causal random fields: here the dependence is propagated along with preferential directions (see [17] for an example of application). It is natural to model the generation of pictures by a non-causal random field defined over a two-dimensional lattice. In this case, the completion problem consists in filling missing pixels using neighboring pixels [4]. Another application of importance is the case of completing geographical data sets which make sense for an ecology setting (see http://doukhan.u-cergy.fr/EcoDep.html), for which applications are of fundamental importance

Our contribution
Outline of the paper
Some definitions and notations
Local non-causal relations
Contraction hypothesis
Coupling hypothesis
Examples We provide below some examples of non-causal random fields
Function of interest Φ and the statistic SI
Main Results
Concentration inequalities and expected deviation bounds for non-causal random fields
Comparison with other results
Application to the completion problem
Model selection
Approximation
Notations
Exact reconstruction
Intuition
Definition
Approximation error
Counting random variables
An extention of McDiarmid’s inequality
McDiarmid’s inequality
General concentration inequalities
Concentration inequalities with optimized parameters
Expected deviation bounds
Full Text
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