J. Zhu, A. Ahmed and E.P. Xing Carnegie Mellon University ICML 2009 MedLDA: Maximum Margin Supervised Topic Models for Regression and Classification J. Zhu, A. Ahmed and E.P. Xing Carnegie Mellon University ICML 2009 Presented By Haojun Chen Sources: http://www.cs.cmu.edu/~junzhu/medlda.htm
Outline Motivation Supervised topic model (sLDA) and Support vector regression (SVR) Maximum entropy discrimination LDA (MedLDA) MedLDA for Regression MedLDA for Classification Experiments Results Conclusion
Motivation Learning latent topic models with side information, like sLDA, has attracted increasingly attention. Maximum likelihood estimation are used for posterior inference and parameter estimation in sLDA. Max-margin methods, such as SVM, for classification have demonstrated success in many applications. General principle for learning max-margin discriminative supervised latent topic models for both regression and classification is proposed in this paper.
Supervised Topic Model (sLDA) Joint distribution for sLDA Variational MLE for sLDA
Support Vector Regression (SVR) Given a training set , the linear SVR finds an optimal linear function by solving the following constrained convex optimization problem
Max-Entropy Discrimination LDA (MedLDA) Maximum entropy discrimination LDA (MedLDA): an integration of max-margin prediction models (e.g. SVR and SVM) and hierarchical Bayesian topic models (e.g. LDA and sLDA) Specifically, a distribution is learned in a max-margin manner in MedLDA. MedLDA for regression and classification are considered in this paper.
MedLDA for Regression For regression, MedLDA is defined as an integration of Bayesian sLDA and SVR is the variational approximation for the posterior
EM Algorithm for MedLDA Regression Variational EM Algorithm: The key difference between sLDA and MedLDA lies in updating
MedLDA for Classification Similar to the regression model, the integrated LDA and multi-class classification model is defined as follow: where
EM Algorithm for MedLDA Classification Similar to the EM algorithm for MedLDA regression Update equation for
Embedding Results 20 Newsgroup dataset MedLDA LDA
Example Topics Discovered
Classification Results 20 Newsgroup Data Relative ratio =
Regression Results Movei Review Data
Time Efficiency
Conclusion MedLDA: an integration of max-margin prediction models and hierarchical Bayesian topic models by optimizing a single objective function with a set of expected margin constraints