One-dimensional infinite memory imitation models with noise

In this paper we study stochastic process indexed by $\mathbb {Z}$ constructed from certain transition kernels depending on the whole past. These kernels prescribe that, at any time, the current state is selected by looking only at a previous random instant. We characterize uniqueness in terms of simple concepts concerning families of stochastic matrices, generalizing the results previously obtained in De Santis and Piccioni (J. Stat. Phys., 150(6):1017--1029, 2013).Comment: 22 pages, 3 figure

Class Schema Evolution for Persistent Object-Oriented Software: Model, Empirical Study, and Automated Support

With the wide support for object serialization in object-oriented programming languages, persistent objects have become common place and most large object-oriented software systems rely on extensive amounts of persistent data. Such systems also evolve over time. Retrieving previously persisted objects from classes whose schema has changed is however difficult, and may lead to invalidating the consistency of the application. The ESCHER framework addresses these issues through an IDE-integrated approach that handles class schema evolution by managing versions of the code and generating transformation functions automatically. The infrastructure also enforces class invariants to prevent the introduction of potentially corrupt objects. This article describes a model for class attribute changes, a measure for class evolution robustness, four empirical studies, and the design and implementation of the ESCHER system.Comment: 14 pages, to appear in IEEE Transactions on Software Engineering (TSE

Dirichlet random walks

This article provides tools for the study of the Dirichlet random walk in $\mathbb{R}^d$. By this we mean the random variable $W=X_1\Theta_1+\cdots+X_n\Theta_n$ where $X=(X_1,\ldots,X_n) \sim \mathcal{D}(q_1,\ldots,q_n)$ is Dirichlet distributed and where $\Theta_1,\ldots \Theta_n$ are iid, uniformly distributed on the unit sphere of $\mathbb{R}^d$ and independent of $X.$ In particular we compute explicitely in a number of cases the distribution of $W.$ Some of our results appear already in the literature, in particular in the papers by G\'erard Le Ca\"{e}r (2010, 2011). In these cases, our proofs are much simpler from the original ones, since we use a kind of Stieltjes transform of $W$ instead of the Laplace transform: as a consequence the hypergeometric functions replace the Bessel functions. A crucial ingredient is a particular case of the classical and non trivial identity, true for $0\leq u\leq 1/2$:$$_2F_1(2a,2b;a+b+\frac{1}{2};u)= \_2F_1(a,b;a+b+\frac{1}{2};4u-4u^2).$$ We extend these results to a study of the limits of the Dirichlet random walks when the number of added terms goes to infinity, interpreting the results in terms of an integral by a Dirichlet process. We introduce the ideas of Dirichlet semigroups and of Dirichlet infinite divisibility and characterize these infinite divisible distributions in the sense of Dirichlet when they are concentrated on the unit ball of $\mathbb{R}^d.$ {4mm}\noindent \textsc{Keywords:} Dirichlet processes, Stieltjes transforms, random flight, distributions in a ball, hyperuniformity, infinite divisibility in the sense of Dirichlet. {4mm}\noindent \textsc{AMS classification}: 60D99, 60F99

Optimal Scaling of Mala for Nonlinear Regression

We address the problem of simulating efficiently from the posterior distribution over the parameters of a particular class of nonlinear regression models using a Langevin-Metropolis sampler. It is shown that as the number N of parameters increases, the proposal variance must scale as N{-1/3} in order to converge to a diffusion. This generalizes previous results of Roberts and Rosenthal [J. R. Stat. Soc. Ser. B Stat. Methodol. 60 (1998) 255-268] for the i.i.d. case, showing the robustness of their analysis

Cortesía y lenguas de especialidad entre lo local y lo global: el caso de las reseñas de hoteles en español e inglés

El presente trabajo analiza el género de la reseña de hoteles en español y en inglés para explorar la evolución de este género a raíz de su internacionalización. El análisis basado en corpus se realiza a través de una comparación monolingüe y bilingüe contrastiva, observando la distribución de estrategias de atenuación e intensificación (Briz, 2001; Albelda, 2007) de los adjetivos con carga semántica negativa en tres tipos de reseñas: reseñas en español publicadas en plataformas nacionales españolas, reseñas en español publicadas en plataformas internacionales, y reseñas en inglés publicadas en plataformas internacionales. Los resultados cuantitativos demuestran que la difusión global de estos textos promueve la fidelidad al género internacional más que a la tradición discursiva de la lengua y cultura nacionales, al mismo tiempo que limita los rasgos lingüísticos típicos de lo coloquial, dando paso a una nueva forma de comunicación especializada.This paper analyses hotel reviews in Spanish and English to explore the evolution of this genre as a consequence of its availability on the globalised tourism market. A corpus-based comparison (monolingual and bilingual contrastive) is carried out of hedging and intensifying strategies (Briz, 2001; Albelda, 2007) used to modify semantically negative adjectives. The distribution of these strategies is observed across 3 corpora comprising respectively: reviews in Spanish published on Spanish platforms; reviews in Spanish published on international platforms; reviews in English published on international platforms. Quantitative results show that global circulation of this genre promotes convergence towards the international genre rather than preservation of the national discourse tradition; such convergence discourages the use of linguistic traits typical of informal settings, giving rise to a new form of specialised communication