2,930 research outputs found

    Randomized parallel approximations to max flow

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

    Parallel algorithms for two processors precedence constraint scheduling

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

    On parallel versus sequential approximation

    Get PDF
    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 epsilon1epsilon_1, epsilon2epsilon_2 such that although the problem can be approximated in P within epsilon1epsilon_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

    Get PDF
    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

    Diaglexia: manual de usuario de una aplicación informática para el diagnóstico de la dislexia (II)

    Get PDF
    [Resumen] En esta segunda parte, queremos presentar el manual de usuario para la aplicación de nuestro programa Diaglexia, ya que en la primera parte sólo presentamos algunas pantallas que reflejan la evaluación que se pretende llevar a cabo con el sujeto que presente problemas lectoescritores. Realmente queremos facilitar la tarea tanto del profesional, en el que puede crear sus propias pruebas diagnóstica adaptándose a la problemática individual del discent

    Diaglexia: una aplicación informática para el diagnóstico de la dislexia

    Get PDF
    [Resumen] En esta comunicación pretendemos dar una opción diferente al profesor de Audición y Lenguaje, al Logopeda o al Psicopedagogo de un departamento de orientación, a la hora de hacer un diagnóstico a un discente con trastornos lectoescritores, en concreto la dislexia. Se trata de una aplicación informática llamada Diaglexia,en la que se ponen a disposición del niño las herramientas de la nueva era, la tecnología informática. Se pretende explorar los fallos del sujeto a la vez que se divierte, realmente este programa pide una segunda parte, en el que se propongan diversas actividades para la intervención o reeducación de la dislexia. Por otra parte, hay una segunda comunicación que explica el manual de usuari

    Web apps and imprecise probabilities

    Get PDF
    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

    Get PDF
    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

    Get PDF
    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

    Hot carrier and hot phonon coupling during ultrafast relaxation of photoexcited electrons in graphene

    Get PDF
    We study, by means of a Monte Carlo simulator, the hot phonon effect on the relaxation dynamics in photoexcited graphene and its quantitative impact as compared to considering an equilibrium phonon distribution. Our multi-particle approach indicates that neglecting the hot phonon effect significantly underestimates the relaxation times in photoexcited graphene. The hot phonon effect is more important for a higher energy of the excitation pulse and photocarrier densities between 11 and 3×1012 cm−23\times 10^{12} \mathrm{~cm}^{-2}. Acoustic intervalley phonons play a non-negligible role, and emitted phonons with wavelengths limited up by a maximum (determined by the carrier concentration) induce a slower carrier cooling rate. Intrinsic phonon heating is damped in graphene on a substrate due to additional cooling pathways, with the hot phonon effect showing a strong inverse dependence with the carrier density.Comment: 12 pages, 5 figure
    • …
    corecore