4,251 research outputs found
A Henneberg-based algorithm for generating tree-decomposable minimally rigid graphs
In this work we describe an algorithm to generate tree-decomposable minimally rigid graphs on a given set of vertices V . The main idea is based on the well-known fact that all minimally rigid graphs, also known as Laman graphs, can be generated via Henneberg sequences. Given that not each minimally rigid graph is tree-decomposable, we identify a set of conditions on the way Henneberg steps are applied so that the resulting graph is tree-decomposable. We show that the worst case running time of the algorithm is O(|V|3).Postprint (author's final draft
Unsupervised learning of human motion
An unsupervised learning algorithm that can obtain a probabilistic model of an object composed of a collection of parts (a moving human body in our examples) automatically from unlabeled training data is presented. The training data include both useful "foreground" features as well as features that arise from irrelevant background clutter - the correspondence between parts and detected features is unknown. The joint probability density function of the parts is represented by a mixture of decomposable triangulated graphs which allow for fast detection. To learn the model structure as well as model parameters, an EM-like algorithm is developed where the labeling of the data (part assignments) is treated as hidden variables. The unsupervised learning technique is not limited to decomposable triangulated graphs. The efficiency and effectiveness of our algorithm is demonstrated by applying it to generate models of human motion automatically from unlabeled image sequences, and testing the learned models on a variety of sequences
Sequential sampling of junction trees for decomposable graphs
The junction-tree representation provides an attractive structural property
for organizing a decomposable graph. In this study, we present a novel
stochastic algorithm, which we call the junction-tree expander, for sequential
sampling of junction trees for decomposable graphs. We show that recursive
application of the junction-tree expander, expanding incrementally the
underlying graph with one vertex at a time, has full support on the space of
junction trees with any given number of underlying vertices. A direct
application of our suggested algorithm is demonstrated in a sequential Monte
Carlo setting designed for sampling from distributions on spaces of
decomposable graphs, where the junction-tree expander can be effectively
employed as proposal kernel; see the companion paper Olsson et al. 2019 [16]. A
numerical study illustrates the utility of our approach by two examples: in the
first one, how the junction-tree expander can be incorporated successfully into
a particle Gibbs sampler for Bayesian structure learning in decomposable
graphical models; in the second one, we provide an unbiased estimator of the
number of decomposable graphs for a given number of vertices. All the methods
proposed in the paper are implemented in the Python library trilearn.Comment: 31 pages, 7 figure
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