12,566 research outputs found
Cover Tree Bayesian Reinforcement Learning
This paper proposes an online tree-based Bayesian approach for reinforcement
learning. For inference, we employ a generalised context tree model. This
defines a distribution on multivariate Gaussian piecewise-linear models, which
can be updated in closed form. The tree structure itself is constructed using
the cover tree method, which remains efficient in high dimensional spaces. We
combine the model with Thompson sampling and approximate dynamic programming to
obtain effective exploration policies in unknown environments. The flexibility
and computational simplicity of the model render it suitable for many
reinforcement learning problems in continuous state spaces. We demonstrate this
in an experimental comparison with least squares policy iteration
Model selection via Bayesian information capacity designs for generalised linear models
The first investigation is made of designs for screening experiments where
the response variable is approximated by a generalised linear model. A Bayesian
information capacity criterion is defined for the selection of designs that are
robust to the form of the linear predictor. For binomial data and logistic
regression, the effectiveness of these designs for screening is assessed
through simulation studies using all-subsets regression and model selection via
maximum penalised likelihood and a generalised information criterion. For
Poisson data and log-linear regression, similar assessments are made using
maximum likelihood and the Akaike information criterion for minimally-supported
designs that are constructed analytically. The results show that effective
screening, that is, high power with moderate type I error rate and false
discovery rate, can be achieved through suitable choices for the number of
design support points and experiment size. Logistic regression is shown to
present a more challenging problem than log-linear regression. Some areas for
future work are also indicated
Bayes linear kinematics in the analysis of failure rates and failure time distributions
Collections of related Poisson or binomial counts arise, for example, from a number of different failures in similar machines or neighbouring time periods. A conventional Bayesian analysis requires a rather indirect prior specification and intensive numerical methods for posterior evaluations. An alternative approach using Bayes linear kinematics in which simple conjugate specifications for individual counts are linked through a Bayes linear belief structure is presented. Intensive numerical methods are not required. The use of transformations of the binomial and Poisson parameters is proposed. The approach is illustrated in two examples, one involving a Poisson count of failures, the other involving a binomial count in an analysis of failure times
Active inference and oculomotor pursuit: the dynamic causal modelling of eye movements.
This paper introduces a new paradigm that allows one to quantify the Bayesian beliefs evidenced by subjects during oculomotor pursuit. Subjects' eye tracking responses to a partially occluded sinusoidal target were recorded non-invasively and averaged. These response averages were then analysed using dynamic causal modelling (DCM). In DCM, observed responses are modelled using biologically plausible generative or forward models - usually biophysical models of neuronal activity
Generalisations of Fisher Matrices
Fisher matrices play an important role in experimental design and in data
analysis. Their primary role is to make predictions for the inference of model
parameters - both their errors and covariances. In this short review, I outline
a number of extensions to the simple Fisher matrix formalism, covering a number
of recent developments in the field. These are: (a) situations where the data
(in the form of (x,y) pairs) have errors in both x and y; (b) modifications to
parameter inference in the presence of systematic errors, or through fixing the
values of some model parameters; (c) Derivative Approximation for LIkelihoods
(DALI) - higher-order expansions of the likelihood surface, going beyond the
Gaussian shape approximation; (d) extensions of the Fisher-like formalism, to
treat model selection problems with Bayesian evidence.Comment: Invited review article for Entropy special issue on 'Applications of
Fisher Information in Sciences'. Accepted versio
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