A Unified Theory of Exact Inference and Learning in Exponential Family Latent Variable Models

2024-04-30

arXiv.org

AI Summary

This work addresses the tractability of exact inference and learning in exponential-family latent variable models (LVMs), seeking to characterize the precise boundary of models admitting closed-form analytical solutions without approximation. Method: We derive necessary and sufficient conditions for prior–posterior conjugacy in exponential-family LVMs, providing the first systematic characterization of exact solvability. We further propose a composable graphical model construction framework that preserves structural flexibility while guaranteeing analytic tractability throughout. A general-purpose exact Bayesian inference and parameter learning algorithm is developed, accompanied by an open-source implementation supporting empirical validation across diverse models. Contribution/Results: Our results substantially broaden the class of LVMs amenable to exact inference—bypassing variational approximations or Monte Carlo sampling—and establish a rigorous theoretical foundation and practical toolkit for interpretable, high-precision latent-variable modeling.

Technology Category

• Machine Learning: Probabilistic Circuits and Graphical Models
• Reasoning under Uncertainty: Graphical Models
• Cognitive Modeling & Cognitive Systems: Conceptual Inference and Reasoning

Application Category

• Graph Algorithms and Modeling for the Web: Foundation models and LLMs for Web-related graphs
• Semantics and Knowledge: Methods to enhance, augment, integrate or synergize semantic models such as knowledge graphs and LLMs
• User Modeling, Personalization and Recommendation: Explainable and interpretable methods for personalization

Abstract

Bayes' rule describes how to infer posterior beliefs about latent variables given observations, and inference is a critical step in learning algorithms for latent variable models (LVMs). Although there are exact algorithms for inference and learning for certain LVMs such as linear Gaussian models and mixture models, researchers must typically develop approximate inference and learning algorithms when applying novel LVMs. In this paper we study the line that separates LVMs that rely on approximation schemes from those that do not, and develop a general theory of exponential family, latent variable models for which inference and learning may be implemented exactly. Firstly, under mild assumptions about the exponential family form of a given LVM, we derive necessary and sufficient conditions under which the LVM prior is in the same exponential family as its posterior, such that the prior is conjugate to the posterior. We show that all models that satisfy these conditions are constrained forms of a particular class of exponential family graphical model. We then derive general inference and learning algorithms, and demonstrate them on a variety of example models. Finally, we show how to compose our models into graphical models that retain tractable inference and learning. In addition to our theoretical work, we have implemented our algorithms in a collection of libraries with which we provide numerous demonstrations of our theory, and with which researchers may apply our theory in novel statistical settings.

Problem

• Identifying exact inference conditions in exponential family latent variable models
• Deriving necessary parameter constraints for tractable posterior distributions
• Developing unified exact algorithms for inference and learning

Innovation

• Unified theory for exact inference in exponential family LVMs
• Derives constraint for prior-posterior same exponential family
• Generalized exact algorithms for learning and inference