3,245 research outputs found
Collaborative Hierarchical Sparse Modeling
Sparse modeling is a powerful framework for data analysis and processing.
Traditionally, encoding in this framework is done by solving an l_1-regularized
linear regression problem, usually called Lasso. In this work we first combine
the sparsity-inducing property of the Lasso model, at the individual feature
level, with the block-sparsity property of the group Lasso model, where sparse
groups of features are jointly encoded, obtaining a sparsity pattern
hierarchically structured. This results in the hierarchical Lasso, which shows
important practical modeling advantages. We then extend this approach to the
collaborative case, where a set of simultaneously coded signals share the same
sparsity pattern at the higher (group) level but not necessarily at the lower
one. Signals then share the same active groups, or classes, but not necessarily
the same active set. This is very well suited for applications such as source
separation. An efficient optimization procedure, which guarantees convergence
to the global optimum, is developed for these new models. The underlying
presentation of the new framework and optimization approach is complemented
with experimental examples and preliminary theoretical results.Comment: To appear in CISS 201
N=2 Einstein-Yang-Mills' static two-center solutions
We construct bona fide one- and two-center supersymmetric solutions to N=2,
d=4 supergravity coupled to SU(2) non-Abelian vector multiplets. The solutions
describe black holes and global monopoles alone or in equilibrium with each
other and exhibit non-Abelian hairs of different kinds.Comment: 46 pages, 1 figure; v2 references adde
Resolution of SU(2) monopole singularities by oxidation
We show how "colored" SU(2) BPS monopoles (that is: SU(2) monopoles
satisfying the Bogomol'nyi equation whose Higgs field and magnetic charge
vanish at infinity and which are singular at the origin) can be obtained from
the BPST instanton by a singular dimensional reduction, explaining the origin
of the singularity and implying that the singularity can be cured by the
oxidation of the solution. We study the oxidation of other monopole solutions
in this scheme.Comment: 13 pages, LaTeX file, no figure
Analysis of Gaussian Quadratic Forms with Application to Statistical Channel Modeling
Finalmente, en el contexto de modelado de canal, la metodologÃa de análisis de variables propuesta permite obtener dos nuevas generalizaciones del conocido modelo de desvanecimiento kappa-mu shadowed. Estas dos nuevas distribuciones, nombradas Beckmann fluctuante y kappa-mu shadowed correlado, incluyen como casos particulares a la gran mayorÃa de distribuciones de desvanecimientos usadas en la literatura, abarcando desde los modelos clásicos de Rayleigh y Rice hasta otros más generales y complejos como el Beckmann y el kappa-mu. Para ambas distribuciones, se presenta su caracterización estadÃstica de primer orden, i.e., función generadora de momentos (MGF), PDF y CDF; asà como los estadÃsticos de segundo orden del modelo Beckmann fluctuante. Fecha de lectura de Tesis Doctoral: 24 Enero 2020En esta tesis se presenta una nueva aproximación a la distribución de de formas cuadráticas gaussianas (FCGs) no centrales tanto en variables reales como complejas. Para ello, se propone un nuevo método de análisis de variables aleatorias que, en lugar de centrarse en el estudio de la variable en cuestión, se basa en la caracterización estadÃstica de una secuencia de variables aleatorias auxiliares convenientemente definida. Como consecuencia, las expresiones obtenidas, con independencia del grado de precisión adquirido, siempre representan una distribución válida, siendo ésta su principal ventaja.
Aplicando este método, se obtienen simples expresiones recursivas para la función densidad de probabilidad (PDF) y la función de distribución (CDF) de las FCGs reales definidas positivas. En el caso de las formas complejas, esta nueva forma de análisis conduce a aproximaciones para los estadÃsticos de primer orden en términos de funciones elementales (exponenciales y potencias), siendo más convenientes para cálculos posteriores que otras soluciones disponibles en la literatura. La tratabilidad matemática se ejemplifica mediante el análisis de sistemas de combinación por razón máxima (MRC) sobre canales Rice correlados, proporcionando aproximaciones cerradas para la probabilidad de outage y la probabilidad de error de bit
Non-Abelian black holes in string theory
We study a family of 5-dimensional non-Abelian black holes that can be
obtained by adding an instanton field to the well-known D1D5W Abelian black
holes. Naively, the non-Abelian fields seem to contribute to the black-hole
entropy but not to the mass due to their rapid fall-off at spatial infinity. By
uplifting the 5-dimensional supergravity solution to 10-dimensional Heterotic
Supergravity first and then dualizing it into a Type-I Supergravity solution,
we show that the non-Abelian fields are associated to D5-branes dissolved into
the D9-branes (dual to the Heterotic "gauge 5-branes") and that their
associated RR charge does not, in fact, contribute to the entropy, which only
depends on the number16 pages of D-strings and D5 branes and the momentum along
the D-strings, as in the Abelian case. These "dissolved" or "gauge" D5-branes
do contribute to the mass in the expected form. The correct interpretation of
the 5-dimensional charges in terms of the string-theory objects solves the
non-Abelian hair puzzle, allowing for the microscopic accounting of the
entropy. We discuss the validity of the solution when alpha prime corrections
are taken into account.Comment: Latex 2e file, 21 pages. A full appendix on alpha prime corrections
and the corresponding discussions have been added. The conclusions have
suffered minor changes. Version accepted in JHE
MEDEA: A DSGE Model for the Spanish Economy
In this paper, we provide a brief introduction to a new macroeconometric model of the Spanish economy named MEDEA (Modelo de Equilibrio Dinámico de la EconomÃa EspañolA). MEDEA is a dynamic stochastic general equilibrium (DSGE) model that aims to describe the main features of the Spanish economy for policy analysis, counterfactual exercises, and forecasting. MEDEA is built in the tradition of New Keynesian models with real and nominal rigidities, but it also incorporates aspects such as a small open economy framework, an outside monetary authority such as the ECB, and population growth, factors that are important in accounting for aggregate fluctuations in Spain. The model is estimated with Bayesian techniques and data from the last two decades. Beyond describing the properties of the model, we perform different exercises to illustrate the potential of MEDEA, including historical decompositions, long-run and short-run simulations, and counterfactual experiments.DSGE Models, Likelihood Estimation, Bayesian Methods
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