Econometrics on GPUs

A graphical processing unit (GPU) is a hardware device normally used to manipulate computer memory for the display of images. GPU computing is the practice of using a GPU device for scientific or general purpose computations that are not necessarily related to the display of images. Many problems in econometrics have a structure that allows for successful use of GPU computing. We explore two examples. The first is simple: repeated evaluation of a likelihood function at different parameter values. The second is a more complicated estimator that involves simulation and nonparametric fitting. We find speedups from 1.5 up to 55.4 times, compared to computations done on a single CPU core. These speedups can be obtained with very little expense, energy consumption, and time dedicated to system maintenance, compared to equivalent performance solutions using CPUs. Code for the examples is provided.

Implementació dels codis de Golay en el paquet matemàtic SAGE

La motivació del present treball va sorgir de la necessitat de descodificar els codis de Golay, un tipus de codis lineals perfectes, en el paquet matemàtic Sage. Sage és un paquet software de lliure distribució i en actual desenvolupament i popularització destinat a aglutinar les funcionalitats de part dels paquets d'anàlisi matemàtic, calculadors simbòlics i manipuladors algebraics propietaris com Mathematica, Matlab, Maple, Magma. En el document es descriurà la implementació realitzada, destacant-ne els aspectes més rellevants. Per a tal efecte, es donarà una introducció als codis lineals i als seus aspectes matemàtics tant des de la vessant de la definició com de les propietats; i al paquet Sage.

Predictions from information-theoretical models of nonequilibrium radiation

The radiation distribution function used by Domínguez and Jou [Phys. Rev. E 51, 158 (1995)] has been recently modified by Domínguez-Cascante and Faraudo [Phys. Rev. E 54, 6933 (1996)]. However, in these studies neither distribution was written in terms of directly measurable quantities. Here a solution to this problem is presented, and we also propose an experiment that may make it possible to determine the distribution function of nonequilibrium radiation experimentally. The results derived do not depend on a specific distribution function for the matter content of the system

Categorization of bibsonomy tags to apply privacy-preserving mechanisms.

In this technical report, we approach one of the practical aspects when it comes to represent users' interests from their tagging activity, namely the categorization of tags into high-level categories of interest. The reason is that the representation of user profiles on the basis of the myriad of tags available on the Web is certainly unfeasible from various practical perspectives; mainly concerningthe unavailability of data to reliably, accurately measure interests across such fine-grained categorization, and, should the data be available, its overwhelming computational intractability. Motivated by this, our study presents the results of a categorization process whereby a collection of tags posted at BibSonomy #http://www.bibsonomy.org# are classified into 5 categories of interest. The methodology used to conduct such categorization is in line with other works in the field.

Hierarchical categorisation of tags for delicious

In the scenario of social bookmarking, a user browsing the Web bookmarks web pages and assigns free-text labels (i.e., tags) to them according to their personal preferences. In this technical report, we approach one of the practical aspects when it comes to represent users' interests from their tagging activity, namely the categorization of tags into high-level categories of interest. The reason is that the representation of user profiles on the basis of the myriad of tags available on the Web is certainly unfeasible from various practical perspectives; mainly concerning the unavailability of data to reliably, accurately measure interests across such fine-grained categorisation, and, should the data be available, its overwhelming computational intractability. Motivated by this, our study presents the results of a categorization process whereby a collection of tags posted at Delicious #http://delicious.com# are classified into 200 subcategories of interest.

Fronts from complex two-dimensional dispersal kernels: theory and application to Reid's paradox

Bimodal dispersal probability distributions with characteristic distances differing by several orders of magnitude have been derived and favorably compared to observations by Nathan [Nature (London) 418, 409 (2002)]. For such bimodal kernels, we show that two-dimensional molecular dynamics computer simulations are unable to yield accurate front speeds. Analytically, the usual continuous-space random walks (CSRWs) are applied to two dimensions. We also introduce discrete-space random walks and use them to check the CSRW results (because of the inefficiency of the numerical simulations). The physical results reported are shown to predict front speeds high enough to possibly explain Reid's paradox of rapid tree migration. We also show that, for a time-ordered evolution equation, fronts are always slower in two dimensions than in one dimension and that this difference is important both for unimodal and for bimodal kernels

Priors about observables in vector autoregressions

Standard practice in Bayesian VARs is to formulate priors on the autoregressive parameters, but economists and policy makers actually have priors about the behavior of observable variables. We show how this kind of prior can be used in a VAR under strict probability theory principles. We state the inverse problem to be solved and we propose a numerical algorithm that works well in practical situations with a very large number of parameters. We prove various convergence theorems for the algorithm. As an application, we first show that the results in Christiano et al. (1999) are very sensitive to the introduction of various priors that are widely used. These priors turn out to be associated with undesirable priors on observables. But an empirical prior on observables helps clarify the relevance of these estimates: we find much higher persistence of output responses to monetary policy shocks than the one reported in Christiano et al. (1999) and a significantly larger total effect.

Habilidades sociales : Una aplicación al Síndrome de Asperger

Las personas con síndrome de Asperger presentan dificultades para la comprensión del otro, para ponerse en su lugar, para saber distinguir entre engaño, mentira y verdad. Tienen serias dificultades en habilidades sociales, sobre todo en saber escuchar, guardar los turnos de palabra, interesarse y entender los estados emocionales. Por este motivo, utilizando la Teoría de la mente y el Paradigma cognitivo, a través de historias sociales, conversaciones en forma de historietas, modelaje... intentaremos ayudar a estas personas a vivir sin estrés sus relaciones sociales para que éstas sean más ajustadas y gratificantes.

Multiuser detection in a dynamic environment — Part II: Joint user identification and parameter estimation

The problem of jointly estimating the number, the identities, and the data of active users in a time-varying multiuser environment was examined in a companion paper (IEEE Trans. Information Theory, vol. 53, no. 9, September 2007), at whose core was the use of the theory of finite random sets on countable spaces. Here we extend that theory to encompass the more general problem of estimating unknown continuous parameters of the active-user signals. This problem is solved here by applying the theory of random finite sets constructed on hybrid spaces. We doso deriving Bayesian recursions that describe the evolution withtime of a posteriori densities of the unknown parameters and data.Unlike in the above cited paper, wherein one could evaluate theexact multiuser set posterior density, here the continuous-parameter Bayesian recursions do not admit closed-form expressions. To circumvent this difficulty, we develop numerical approximationsfor the receivers that are based on Sequential Monte Carlo (SMC)methods (“particle filtering”). Simulation results, referring to acode-divisin multiple-access (CDMA) system, are presented toillustrate the theory.

On iterative performance of LDPC and Root-LDPC codes over block-fading channels

This paper presents our investigation on iterativedecoding performances of some sparse-graph codes on block-fading Rayleigh channels. The considered code ensembles are standard LDPC codes and Root-LDPC codes, first proposed in and shown to be able to attain the full transmission diversity. We study the iterative threshold performance of those codes as a function of fading gains of the transmission channel and propose a numerical approximation of the iterative threshold versus fading gains, both both LDPC and Root-LDPC codes.Also, we show analytically that, in the case of 2 fading blocks,the iterative threshold root of Root-LDPC codes is proportional to (α1 α2)1, where α1 and α2 are corresponding fading gains.From this result, the full diversity property of Root-LDPC codes immediately follows.

Fading models and metrics for contemporary wireless systems

The purpose of this paper is to examine (1) some of the models commonly used to represent fading,and (2) the information-theoretic metrics most commonly used to evaluate performance over those models. We raise the question of whether these models and metrics remain adequate in light of the advances that wireless systems haveundergone over the last two decades. Weaknesses are pointedout, and ideas on possible fixes are put forth.

Ontologies: a review

En aquest paper, analitzem les principals ontologies amb la finalitat de dibuixar un panorama general d'una de les eines més utilitzades en l'estructuració del coneixement. En primer lloc, presentem una àmplia descripció de les cinc ontologies més difoses entre la comunitat científica dedicada a la gestió de la informació. Seguidament, repassem breument algunes de les eines de gestió que s'utilitzen per crear i actualitzar ontologies. I, finalment, presentem algunes conclusions en relació a la selecció d'una ontologia i d'un sistema de gestió per a la seva utilització en el marc dels projectes vigents del grup IULATERM.

Traduir Oscar Wilde: vicissituds pràctiques i implicacions teòriques

A partir d’uns quants entrebancs en la tasca de la traducció al català de l’obra An Ideal Husband d’Oscar Wilde (anomenats 'anècdotes'), s’observen i s’analitzen determinats conceptes teòrics sobre la traducció i algunes consideracions generals sobre l’especificitat de la traducció teatral (dites 'categories'), com són els de funcionalitat, representabilitat, fluïdesa, visibilitat, equivalència, reescriptura, fidelitat, adequació, acceptabilitat o estrangerització. La consideració d’aquests valors manejats per la teoria de la traducció entra aquí en diàleg amb les vicissituds de la pràctica de la traducció dramàtica, diàleg del qual resulta una reafirmació d’alguns d’aquests valors i, per contra, l’evidència de l’escassa productivitat (almenys amb caràcter universal) d’alguns altres