121 research outputs found
Online approximations for wind-field models
We study online approximations to Gaussian process models for spatially distributed systems. We apply our method to the prediction of wind fields over the ocean surface from scatterometer data. Our approach combines a sequential update of a Gaussian approximation to the posterior with a sparse representation that allows to treat problems with a large number of observations
Sequential design of computer experiments for the estimation of a probability of failure
This paper deals with the problem of estimating the volume of the excursion
set of a function above a given threshold,
under a probability measure on that is assumed to be known. In
the industrial world, this corresponds to the problem of estimating a
probability of failure of a system. When only an expensive-to-simulate model of
the system is available, the budget for simulations is usually severely limited
and therefore classical Monte Carlo methods ought to be avoided. One of the
main contributions of this article is to derive SUR (stepwise uncertainty
reduction) strategies from a Bayesian-theoretic formulation of the problem of
estimating a probability of failure. These sequential strategies use a Gaussian
process model of and aim at performing evaluations of as efficiently as
possible to infer the value of the probability of failure. We compare these
strategies to other strategies also based on a Gaussian process model for
estimating a probability of failure.Comment: This is an author-generated postprint version. The published version
is available at http://www.springerlink.co
Bayesian classification of tumours by using gene expression data
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75678/1/j.1467-9868.2005.00498.x.pd
Simultaneous model-based clustering and visualization in the Fisher discriminative subspace
Clustering in high-dimensional spaces is nowadays a recurrent problem in many
scientific domains but remains a difficult task from both the clustering
accuracy and the result understanding points of view. This paper presents a
discriminative latent mixture (DLM) model which fits the data in a latent
orthonormal discriminative subspace with an intrinsic dimension lower than the
dimension of the original space. By constraining model parameters within and
between groups, a family of 12 parsimonious DLM models is exhibited which
allows to fit onto various situations. An estimation algorithm, called the
Fisher-EM algorithm, is also proposed for estimating both the mixture
parameters and the discriminative subspace. Experiments on simulated and real
datasets show that the proposed approach performs better than existing
clustering methods while providing a useful representation of the clustered
data. The method is as well applied to the clustering of mass spectrometry
data
Shop stewardsâ leadership, left-wing activism and collective workplace union organisation
Providing an account of the dynamic interrelationship between shop steward leadership and membership interaction, Ralph Darlington focuses particular attention on the much-neglected crucial role that left-wing political activists can play in shaping the nature of collective workplace relations
Genome-assisted prediction of a quantitative trait measured in parents and progeny: application to food conversion rate in chickens
Accuracy of prediction of yet-to-be observed phenotypes for food conversion rate (FCR) in broilers was studied in a genome-assisted selection context. Data consisted of FCR measured on the progeny of 394 sires with SNP information. A Bayesian regression model (Bayes A) and a semi-parametric approach (Reproducing kernel Hilbert Spaces regression, RKHS) using all available SNPs (p = 3481) were compared with a standard linear model in which future performance was predicted using pedigree indexes in the absence of genomic data. The RKHS regression was also tested on several sets of pre-selected SNPs (p = 400) using alternative measures of the information gain provided by the SNPs. All analyses were performed using 333 genotyped sires as training set, and predictions were made on 61 birds as testing set, which were sons of sires in the training set. Accuracy of prediction was measured as the Spearman correlation (rÂŻS) between observed and predicted phenotype, with its confidence interval assessed through a bootstrap approach. A large improvement of genome-assisted prediction (up to an almost 4-fold increase in accuracy) was found relative to pedigree index. Bayes A and RKHS regression were equally accurate (rÂŻS = 0.27) when all 3481 SNPs were included in the model. However, RKHS with 400 pre-selected informative SNPs was more accurate than Bayes A with all SNPs
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