79,818 research outputs found
Telescoping Recursive Representations and Estimation of Gauss-Markov Random Fields
We present \emph{telescoping} recursive representations for both continuous
and discrete indexed noncausal Gauss-Markov random fields. Our recursions start
at the boundary (a hypersurface in , ) and telescope inwards.
For example, for images, the telescoping representation reduce recursions from
to , i.e., to recursions on a single dimension. Under
appropriate conditions, the recursions for the random field are linear
stochastic differential/difference equations driven by white noise, for which
we derive recursive estimation algorithms, that extend standard algorithms,
like the Kalman-Bucy filter and the Rauch-Tung-Striebel smoother, to noncausal
Markov random fields.Comment: To appear in the Transactions on Information Theor
Recursive image sequence segmentation by hierarchical models
This paper addresses the problem of image sequence segmentation. A technique using a sequence model based on compound random fields is presented. This technique is recursive in the sense that frames are processed in the same cadency as they are produced. New regions appearing in the sequence are detected by a morphological procedure.Peer ReviewedPostprint (published version
Recursive estimation for 2-D isotropic random fields
Bibliography: p. 27-29.National Science Foundation grant no. ECS-83-12921 Army Research Office grant no. DAAG-84-K-0005Ahmed H. Tewfik, Bernard C. Levy, Alan S. Willsky
Chain of matrices, loop equations and topological recursion
Random matrices are used in fields as different as the study of
multi-orthogonal polynomials or the enumeration of discrete surfaces. Both of
them are based on the study of a matrix integral. However, this term can be
confusing since the definition of a matrix integral in these two applications
is not the same. These two definitions, perturbative and non-perturbative, are
discussed in this chapter as well as their relation. The so-called loop
equations satisfied by integrals over random matrices coupled in chain is
discussed as well as their recursive solution in the perturbative case when the
matrices are Hermitean.Comment: 28 pages, 1 figure, contribution to The Oxford Handbook of Random
Matrix Theor
An Introduction to Recursive Partitioning: Rationale, Application and Characteristics of Classification and Regression Trees, Bagging and Random Forests
Recursive partitioning methods have become popular and widely used tools for nonparametric regression and classification in many scientific fields. Especially random forests, that can deal with large numbers of predictor variables even in the presence of complex interactions, have been applied successfully in genetics, clinical medicine and bioinformatics within the past few years.
High dimensional problems are common not only in genetics, but also in some areas of psychological research, where only few subjects can be measured due to time or cost constraints, yet a large amount of data is generated for each subject. Random forests have been shown to achieve a high prediction accuracy in such applications, and provide descriptive variable importance measures reflecting the impact of each variable in both main effects and interactions.
The aim of this work is to introduce the principles of the standard recursive partitioning methods as well as recent methodological improvements, to illustrate their usage for low and high dimensional data exploration, but also to point out limitations of the methods and potential pitfalls in their practical application.
Application of the methods is illustrated using freely available implementations in the R system for statistical computing
Hierarchical semi-markov conditional random fields for recursive sequential data
Inspired by the hierarchical hidden Markov models (HHMM), we present the hierarchical semi-Markov conditional random field (HSCRF), a generalisation of embedded undirected Markov chains to model complex hierarchical, nested Markov processes. It is parameterised in a discriminative framework and has polynomial time algorithms for learning and inference. Importantly, we develop efficient algorithms for learning and constrained inference in a partially-supervised setting, which is important issue in practice where labels can only be obtained sparsely. We demonstrate the HSCRF in two applications: (i) recognising human activities of daily living (ADLs) from indoor surveillance cameras, and (ii) noun-phrase chunking. We show that the HSCRF is capable of learning rich hierarchical models with reasonable accuracy in both fully and partially observed data cases.<br /
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