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 Statistical Learning




Fast Feature Selection from Microarray Expression Data via Multiplicative Large Margin Algorithms

Neural Information Processing Systems

New feature selection algorithms for linear threshold functions are described whichcombine backward elimination with an adaptive regularization method. This makes them particularly suitable to the classification of microarray expression data, where the goal is to obtain accurate rules depending on few genes only. Our algorithms are fast and easy to implement, since they center on an incremental (large margin) algorithm which allows us to avoid linear, quadratic or higher-order programming methods. We report on preliminary experiments with five known DNA microarray datasets. These experiments suggest that multiplicative large margin algorithms tend to outperform additive algorithms (such as SVM) on feature selection tasks.


Locality Preserving Projections

Neural Information Processing Systems

Many problems in information processing involve some form of dimensionality reduction.In this paper, we introduce Locality Preserving Projections (LPP). These are linear projective maps that arise by solving a variational problem that optimally preserves the neighborhood structure of the data set. LPP should be seen as an alternative to Principal Component Analysis(PCA) - a classical linear technique that projects the data along the directions of maximal variance. When the high dimensional datalies on a low dimensional manifold embedded in the ambient space, the Locality Preserving Projections are obtained by finding the optimal linear approximations to the eigenfunctions of the Laplace Beltrami operatoron the manifold.



Gaussian Process Latent Variable Models for Visualisation of High Dimensional Data

Neural Information Processing Systems

In this paper we introduce a new underlying probabilistic model for principal componentanalysis (PCA). Our formulation interprets PCA as a particular Gaussian process prior on a mapping from a latent space to the observed data-space. We show that if the prior's covariance function constrainsthe mappings to be linear the model is equivalent to PCA, we then extend the model by considering less restrictive covariance functions whichallow nonlinear mappings. This more general Gaussian process latent variable model (GPLVM) is then evaluated as an approach to the visualisation of high dimensional data for three different data-sets. Additionally our nonlinear algorithm can be further kernelised leading to'twin kernel PCA' in which a mapping between feature spaces occurs.



New Algorithms for Efficient High Dimensional Non-parametric Classification

Neural Information Processing Systems

This paper is about non-approximate acceleration of high dimensional nonparametric operations such as k nearest neighbor classifiers and the prediction phase of Support Vector Machine classifiers. We attempt to exploit the fact that even if we want exact answers to nonparametric queries, we usually do not need to explicitly find the datapoints close to the query, but merely need to ask questions about the properties about that set of datapoints. This offers a small amount of computational leeway, andwe investigate how much that leeway can be exploited. For clarity, this paper concentrates on pure k-NN classification and the prediction phaseof SVMs. We introduce new ball tree algorithms that on real-world datasets give accelerations of 2-fold up to 100-fold compared against highly optimized traditional ball-tree-based k-NN.


Wormholes Improve Contrastive Divergence

Neural Information Processing Systems

In models that define probabilities via energies, maximum likelihood learning typically involves using Markov Chain Monte Carlo to sample from the model's distribution. If the Markov chain is started at the data distribution, learning often works well even if the chain is only run for a few time steps [3]. But if the data distribution contains modes separated by regions of very low density, brief MCMC will not ensure that different modes have the correct relative energies because it cannot move particles from one mode to another. We show how to improve brief MCMC by allowing long-range moves that are suggested by the data distribution. If the model is approximately correct, these long-range moves have a reasonable acceptance rate.