Randomized parallel approximations to max flow

The final publication is available at link.springer.comPeer ReviewedPostprint (author's final draft

Parallel algorithms for two processors precedence constraint scheduling

The final publication is available at link.springer.comPeer ReviewedPostprint (author's final draft

On parallel versus sequential approximation

In this paper we deal with the class NCX of NP Optimization problems that are approximable within constant ratio in NC. This class is the parallel counterpart of the class APX. Our main motivation here is to reduce the study of sequential and parallel approximability to the same framework. To this aim, we first introduce a new kind of NC-reduction that preserves the relative error of the approximate solutions and show that the class NCX has {em complete} problems under this reducibility. An important subset of NCX is the class MAXSNP, we show that MAXSNP-complete problems have a threshold on the parallel approximation ratio that is, there are positive constants $epsilon_1$, $epsilon_2$ such that although the problem can be approximated in P within $epsilon_1$ it cannot be approximated in NC within epsilon_2$, unless P=NC. This result is attained by showing that the problem of approximating the value obtained through a non-oblivious local search algorithm is P-complete, for some values of the approximation ratio. Finally, we show that approximating through non-oblivious local search is in average NC.Postprint (published version

The parallel approximability of a subclass of quadratic programming

In this paper we deal with the parallel approximability of a special class of Quadratic Programming (QP), called Smooth Positive Quadratic Programming. This subclass of QP is obtained by imposing restrictions on the coefficients of the QP instance. The Smoothness condition restricts the magnitudes of the coefficients while the positiveness requires that all the coefficients be non-negative. Interestingly, even with these restrictions several combinatorial problems can be modeled by Smooth QP. We show NC Approximation Schemes for the instances of Smooth Positive QP. This is done by reducing the instance of QP to an instance of Positive Linear Programming, finding in NC an approximate fractional solution to the obtained program, and then rounding the fractional solution to an integer approximate solution for the original problem. Then we show how to extend the result for positive instances of bounded degree to Smooth Integer Programming problems. Finally, we formulate several important combinatorial problems as Positive Quadratic Programs (or Positive Integer Programs) in packing/covering form and show that the techniques presented can be used to obtain NC Approximation Schemes for "dense" instances of such problems.Peer ReviewedPostprint (published version

Evolution in the Design and Functionality of Rubrics: from “Square” Rubrics to “Federated” Rubrics

The assessment of learning remains one of the most controversial and challenging aspects for teachers. Among some recent technical solutions, methods and techniques like eRubrics emerge in an attempt to solve the situation. Understanding that all teaching contexts are different and there can be no single solution for all cases, specific measures are adapted to contexts where teachers receive support from institutions and communities of practice. This paper presents the evolution of the eRubric service [1] which started from a first experience with paper rubrics, and, with time and after several I+D+R [2] educational projects, has evolved thanks to the support of a community of practice [3] and the exchange of experiences between teachers and researchers. This paper shows the results and functionality of the eRubrics service up to the date of publicationa.) Project I+D+i EDU2010-15432: eRubric federated service for assessing university learning http://erubrica.uma.es/?page_id=434. b.) Centre for the Design of eRubrics. National Distance Education System -Sined- Mexico. [http://erubrica.uma.es/?page_id=389

Web apps and imprecise probabilities

We propose a model for the behaviour of Web apps in the unreliable WWW. Web apps are described by orchestrations. An orchestration mimics the personal use of the Web by defining the way in which Web services are invoked. The WWW is unreliable as poorly maintained Web sites are prone to fail. We model this source of unreliability trough a probabilistic approach. We assume that each site has a probability to fail. Another source of uncertainty is the traffic congestion. This can be observed as a non-deterministic behaviour induced by the variability in the response times. We model non-determinism by imprecise probabilities. We develop here an ex-ante normal to characterize the behaviour of finite orchestrations in the unreliable Web. We show the existence of a normal form under such semantics for orchestrations using asymmetric parallelism.Peer ReviewedPostprint (author's final draft

Measuring satisfaction in societies with opinion leaders and mediators

An opinion leader-follower model (OLF) is a two-action collective decision-making model for societies, in which three kinds of actors are considered:Preprin

Cooperation through social influence

We consider a simple and altruistic multiagent system in which the agents are eager to perform a collective task but where their real engagement depends on the willingness to perform the task of other influential agents. We model this scenario by an influence game, a cooperative simple game in which a team (or coalition) of players succeeds if it is able to convince enough agents to participate in the task (to vote in favor of a decision). We take the linear threshold model as the influence model. We show first the expressiveness of influence games showing that they capture the class of simple games. Then we characterize the computational complexity of various problems on influence games, including measures (length and width), values (Shapley-Shubik and Banzhaf) and properties (of teams and players). Finally, we analyze those problems for some particular extremal cases, with respect to the propagation of influence, showing tighter complexity characterizations.Peer ReviewedPostprint (author’s final draft

Diagnóstico comparativo del test TIDA con otros test de detección de anomalías de la visión del color en una población infantil

Índice, resumen, conclusiones y bibliografía del Trabajo Fin de Grado del Curso de adaptación al Grado de Óptica y Optometría, dirigido por Dolores de Fez Saiz.La percepción del color enriquece nuestra experiencia visual y nos permite distinguir objetos y escenas que de otra forma no podríamos distinguir con claridad. Una misma imagen nos parecería absolutamente distinta si la percibiésemos en blanco y negro en vez de hacerlo en color. Por tanto, la percepción del color es importante para nuestra vida, pero no imprescindible, como queda patente por el hecho de que aproximadamente el diez por ciento de la población masculina padece alguna forma de disfunción en la percepción del color. El hecho de que existan personas con este tipo de alteración ha desencadenado a lo largo del tiempo que muchos científicos estén interesados en estudiar esta forma de percibir la realidad y hayan desarrollado diversos tests para su detección y diagnóstico. El TIDA (Test de Identificación de Daltonismos) ha sido diseñado, según sus autores, para la detección de problemas de la visión del color rojo-verde en niños. La pregunta es si proporciona un buen diagnóstico de las alteraciones de la visión del color. Para ello se han comparado los resultados obtenidos mediante este test en una población infantil con los obtenidos mediante los tests convencionales (láminas de Ishihara y Farnsworth-Munsell 100 Hue) de detección de estas alteraciones. En una muestra de un total de 337 niños/as, se ha utilizado el test de Ishihara para detectar la existencia de alguna anomalía del color. Los sujetos que resultaron ser normal, sólo se le administró el test TIDA con el fin de comprobar si el diagnóstico también era de normalidad. En los que se detectó alguna alteración cromática se realizaron todas las pruebas (añadiendo el test Farnsworth-Munsell) monocularmente. El resultado que se ha obtenido es que el 3,56% (12 niños) fue diagnosticado con algún tipo de alteración de la visión del color. Comparando los resultados obtenidos entre el test Ishihara y el TIDA, en el 62,5% de los casos el diagnóstico es diferente y en el 37,5% es el mismo. Cuando comparamos los resultados obtenidos entre el test FM-100H y el TIDA obtenemos que 72,7% de los casos el resultado es diferente y 27,3% es el mismo. Podemos observar que, en ambos casos, los porcentajes en los que se ha obtenido un diagnóstico diferente son mayores

Radio 5: del todo a la nada en la información autonómica

La reestructuración de RTVE ha provocado un adelgazamiento de la plantilla, de su estructura territorial y de la programación de proximidad en el canal Todo Noticias (TN) de RNE. Los 24 boletines autonómicos diarios que ofrecía Radio 5 TN han desaparecido y cinco autonomías acaparan el 71% de las informaciones emitidas en el ámbito nacional. Se ha producido una centralización de la información que no se acerca al objetivo encomendado a RTVE por la Ley de la Radio y la Televisión de 2006 de servir de motor y garante de los flujos entre las distintas Comunidades en su oferta de contenidos.The restructuring of the Spanish Radio Television (RTVE) has prompted a cutback in its work force, in its territorial structure and in the proximity programming of the channel “Todo Noticias (TN)” of the Spanish National Radio (Radio Nacional de España, RNE). The 24 daily regional bulletins offered by Radio 5 TN have disappeared and only five autonomous regions centralize a 71% of the news broadcast at a national level. Thus, a centralization of the information has been produced, which is far from the objective entrusted to RTVE by the Law of Radio and Television 2006 (Ley de la Radio y la Televisión de 2006) of being the driving force and the guarantor of the offer of contents flow among the several autonomous regions