Nonparametric Bayesian Mixed-effect Model: a Sparse Gaussian Process Approach

Multi-task learning models using Gaussian processes (GP) have been developed and successfully applied in various applications. The main difficulty with this approach is the computational cost of inference using the union of examples from all tasks. Therefore sparse solutions, that avoid using the entire data directly and instead use a set of informative "representatives" are desirable. The paper investigates this problem for the grouped mixed-effect GP model where each individual response is given by a fixed-effect, taken from one of a set of unknown groups, plus a random individual effect function that captures variations among individuals. Such models have been widely used in previous work but no sparse solutions have been developed. The paper presents the first sparse solution for such problems, showing how the sparse approximation can be obtained by maximizing a variational lower bound on the marginal likelihood, generalizing ideas from single-task Gaussian processes to handle the mixed-effect model as well as grouping. Experiments using artificial and real data validate the approach showing that it can recover the performance of inference with the full sample, that it outperforms baseline methods, and that it outperforms state of the art sparse solutions for other multi-task GP formulations.Comment: Preliminary version appeared in ECML201

Identidad y conciencia. Consideraciones en torno a la «Dialéctica Negativa» de Adorno.

Sin resume

A note on the Gauge Symmetries of Unimodular Gravity

The symmetries of Unimodular Gravity are clarified somewhat.Comment: 4 pages, v2: acknowledgments correcte

Charmless B \rightarrow VV decays at LHCb

$B^0_s$ meson decays into non--charmonium vector pairs are of particular interest to search for indirect $CP$ violation. The analyses of two specific decays are presented here, $B_s^0 \rightarrow \phi \phi$ and $B_s^0 \rightarrow K^{*0} \bar{K}^{*0}$. These studies have been performed using, respectively, $1fb^{-1}$ and $35pb^{-1}$ of data collected by LHCb in $pp$ collisions at a centre--of--mass energy of 7 TeV. In $B_s^0 \rightarrow \phi \phi$ decay, the $CP$--violating phase arising in the interference between $B_s^0$--$\bar{B}_s^0$ mixing and the $b\rightarrow s\bar{s}s$ penguin decay has been determined to be in the interval $[-2.46,-0.76]$ rad at 68% confidence level. The first observation of $B_s^0 \rightarrow K^{*0} \bar{K}^{*0}$ decay is also reported. The branching fraction and the $CP$--averaged $K^{*0}$ longitudinal polarization fraction are measured to be $\mathcal{B}(B_s^0 \rightarrow K^{*0} \bar{K}^{*0})$ = (2.81 $\pm$ 0.46(stat.) $\pm$ 0.45(syst.) $\pm$ 0.34($f_s/f_d$))$\times 10^{-5}$ and $f_L$ = 0.31 $\pm$ 0.12(stat.) $\pm$ 0.04(syst.)

Combining interactive GIS tools and expert knowledge in validation of tree species models

Poster presented at XIII Congreso Forestal Mundial. FAO, Buenos Aires (Argentina). 18-25 Oct 200