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Compilation and communication protocols for voting rules with a dynamic set of candidates
No full textWe address the problem of designing communication protocols for voting rules when the set of candidates can evolve via the addition of new candidates. We show that the necessary amount of communication that must be transmitted between the voters and the central authority depends on the amount of space devoted to the storage of the votes over the initial set of candidates. This calls for a bicriteria evaluation of protocols. We consider a few usual voting rules, and three types of storage functions: full storage, where the full votes on the initial set of voters are stored; null storage, where nothing is stored; and anonymous storage, which lies in-between. For some of these pairs (voting rule, type of storage) we design protocols and show that they are asymptotically optimal by determining the communication complexity of the rule under the storage function considered.ouinonouirechercheInternationa
Approximation with a Fixed Number of Solutions of Some Biobjective Maximization Problems
No full textWe investigate the problem of approximating the Pareto set of biobjective optimization problems with a given number of solutions. This task is relevant for two reasons: (i) Pareto sets are often computationally hard so approximation is a necessary tradeoff to allow polynomial time algorithms; (ii) limiting explicitly the size of the approximation allows the decision maker to control the expected accuracy of approximation and prevents him to be overwhelmed with too many alternatives. Our purpose is to exploit general properties that many well studied problems satisfy. We derive existence and constructive approximation results for the biobjective versions of Max Bisection, Max Partition, Max Set Splitting and Max Matching.ouinonouirechercheInternationa
Efficient Algorithms for Finding the k Most Vital Edges for the Minimum Spanning Tree Problem
No full textWe study in this paper the problem of finding in a graph a subset of k edges whose deletion causes the largest increase in the weight of a minimum spanning tree. We propose for this problem an explicit enumeration algorithm whose complexity, when compared to the current best algorithm, is better for general k but very slightly worse for fixed k. More interestingly, unlike in the previous algorithms, we can easily adapt our algorithm so as to transform it into an implicit exploration algorithm based on a branch and bound scheme. We also propose a mixed integer programming formulation for this problem. Computational results show a clear superiority of the implicit enumeration algorithm both over the explicit enumeration algorithm and the mixed integer program.ouinonouirechercheInternationa
Facteurs psychosociaux et continuité d'utilisation des réseaux sociaux numériques : le cas de facebook
No full textDans cet article, nous proposons un modèle explicatif de l'intention de la continuité d'utilisation des réseaux sociaux numériques (RSN), basé sur la théorie du comportement planifié et prenant en compte un facteur psychosocial, qui est le degré de timidité perçue. Nous optons pour une approche quantitative appliquée à 346 utilisateurs de Facebook. Une série d'analyses par les équations structurelles nous a permis de confirmer le rôle déterminant de l'attitude et de la maîtrise comportementale perçue sur l'intention de la continuité d'utilisation de ce site. Le facteur timidité agit négativement sur l'intention de continuer à utiliser Facebook.We propose, in this paper, an explanatory model of the continuance of usage intention of social networking sites based on the theory of planned behavior and taking into account the user's perceived degree of shyness. This research is based on a quantitative methodology. Thanks to a quantitative approach, we collected 346 responses from Facebook users. Our findings suggest that the continuance of usage intention is generally determined by the attitude and the perceived behavioral control. However, social influence does not play a significant role in our model. Surprisingly, shyness has a negative effect on the intention to continue using Facebook.En este trabajo, proponemos un modelo para explicar la intención de la continuidad del uso de las redes sociales, basado en la teoría del comportamiento planificado, y teniendo en cuenta las dimensiones de la personalidad, es decir, el grado percibido de la timidez. Hemos optado por una metodología cuantitativa (346 usuarios de la tecnología digital Facebook). Una serie de análisis de ecuaciones estructurales nos ha permitido confirmar el papel de la actitud y control del comportamiento percibido sobre la intención de la continuidad del uso de esta sitio web. El factor de la timidez es, negativamente sobre la continuidad del uso de Facebook.nonouirechercheNationa
A Reference Model for Knowledge Retention within Small and Medium-sized Enterprises
No full textKnowledge retention (KR) has been identified as one of the critical factors for maintainingsustainableperformance. However, until recently, most of the existing researches have focused on large organizations,while very few studies have mentioned this issue inSmall and Medium-Sized Enterprises (SMEs). Toredress some of this imbalance in the literature, this paper provides a reference model for knowledgeretention within SMEs. This model includes most ofthe fundamental elements that are believed to becritical for an effective KR implementation. The model is especially tailored for SMEs to kick-start aKRinitiative in their organization as well as can beserved as a template to assess the SMEs’ KR maturity level.nonouirechercheInternationa
Dynamic hedging by a large player: From theory to practical implementation
No full textMarket liquidity risk refers to the degree to which large size transactions can be carried out in a timely fashion with a minimal impact on prices. Emphasized by the G10 report in 1993 and the BIS report in 1997, it is viewed as one factor of destabilization in the financial markets, as illustrated recently by the Asian crisis, the faillure of the hedge fund LTCM during the Russian crisis. So in order to assess welfare implications of portfolio insurance strategies, it would be useful to estimate the dynamic hedging activity in securities markets through a specific parsimonious and realistic model. In the paper, large traders hold sufficient liquid assets to meet liquidity needs of other traders, and so bear the risk of their imbalanced derivatives portfolio. Their dynamic hedging strategies entail non-linear positive feedback effects, and in turn buying and selling derivatives at prices shifted by an amount that depends on their net holding. And therefore, the replicating equation turns to be a fully nonlinear parabolic PDE, as proposed by Frey [10]. It turns out that such a nonlinear PDE equation may be numerically unstable when using traditional finite-difference methods. Therefore we need some specific adequate numerical implementation in order to solve this equation with significant accuracy and flexibility, while keeping stability. In this respect paper we devised and customized two different numerical methods: one is a refined finite difference method; the other involves the probabilistic scheme proposed by Fahim and al. [9]. In contrast, another method based on Lie algebra and developed by Bordag and al. only provides a generic, albeit analytical, formulation of solutions, and not the specific one consistent with our payoff. Still, that method offers a reference for our proposed methods in terms of numerical accuracy. Using such a framework, a Large Player is then in a position to take into account those positive feedback effects in dynamic hedging. Lastly, we show how dynamic hedging may directly and endogenously give rise to empirically observed bid-offer spreads.nonouirechercheInternationa
Integrating Cognitive Mapping Analysis into Multi-Criteria Decision Aiding
No full textMulti-criteria decision aiding (MCDA) is a process implying two distinctiveactors (the client and the analyst) which aims at providing transparent andcoherent support for complex decision situations, taking into account valuesof decision makers involved in a speci c decision context. The theoreticalframework of MCDA traditionally addresses problems involving a singledecision maker. However, MCDA ought to investigate the case where thedecision maker is made up of groups of individuals with con icting interests.In contrast, cognitive mapping (CM) is frequently used in order to capturethe values in a group of individuals and to reduce the antagonism betweensuch values. Its ability to capture multiple values and reduce their con ictingaspects provides a rationale for decision problem analysis with multiplestakeholders. Nevertheless, capturing values by CM is not always intendedfor a subsequent multi-criteria analysis.This paper explores the integration of both techniques combining theirrespective strengths as well as their application in assessment of hydrogentechnologies scenarios in terms of their perception and social acceptabilityby the general public.ouinonouirechercheInternationa
Online maximum k-coverage
No full textWe study an online model for the maximumView the MathML source-vertex-coverage problem, in which, given a graph G=(V,E) and an integer View the MathML source, we seek a subset A⊆V such that View the MathML source and the number of edges covered by A is maximized. In our model, at each step i, a new vertex vi is released, and we have to decide whether we will keep it or discard it. At any time of the process, only View the MathML source vertices can be kept in memory; if at some point the current solution already contains View the MathML source vertices, any inclusion of a new vertex in the solution must entail the definite deletion of another vertex of the current solution (a vertex not kept when released is definitely deleted). We propose algorithms for several natural classes of graphs (mainly regular and bipartite), improving on an easy View the MathML source-competitive ratio. We next settle a set version of the problem, called the maximumView the MathML source-(set)-coverage problem. For this problem, we present an algorithm that improves upon former results for the same model for small and moderate values of View the MathML source.ouinonouirechercheInternationa
Le lien entre stimulation sensorielle, sensation thermique et comportement de fuite au sein du point de vente : Une application des lois de Fechner et de Stevens
No full textLa température a fait l'objet de peu de recherche en comportement du consommateur sur le point de vente. Pourtant ce stimulus d'ambiance est d'un intérêt managérial indéniable tant du point de vue du marketing qu'en matière d'économie d'énergie. Les objectifs de cette recherche sont d'investiguer les effets de niveaux de température confortables (19 et 23°C) et d'un niveau de température inconfortable (27°C) sur (1) les perceptions ressenties de température, (2) les perceptions de confort et le comportement effectif des consommateurs (temps passé). A cet effet, nous mobilisons les lois de Fechner et de Stevens, pour les températures chaudes, qui postulent un lien entre stimulus et sensation, tel que la sensation varie comme le logarithme de l'intensité de la stimulation. Les hypothèses sont testées dans le cadre d'une expérimentation en laboratoire, recréant l'environnement d'une librairie, avec les trois conditions de température. Les résultats montrent que les augmentations de température ressentie sont moindres que celles des températures réelles. Ils mettent aussi en évidence l'influence des écarts de température sur les perceptions d'inconfort et les comportements de fuite. En particulier, quand la température s'accroît, le temps passé sur le point de vente diminue, mais moins que proportionnellement à l'augmentation effective de température lorsque l'on sort de la zone de confort. Ces résultats sont conformes aux hypothèses émises et à la littérature en psychophysique et en ergonomie.Temperature is said to have a major impact on retailing management and energy savings. However, few studies have investigated its effect on point of sales' consumer behavior. This research aims at studying the effect of comfortable (19°C and 23°C) and uncomfortable (27°C) levels of temperature on (1) temperature perception and (2) perception of comfort and actual behavior (time spent in store). We base our reasoning on Fechner's and Stevens' laws, for hot temperature, which assume that the sensation varies as the logarithm of the stimulus intensity. We have conducted an experiment in a lab, by creating a mock book store in which the three levels of temperature were carefully controlled. Results show that the perception of increased temperature is lesser than the actual temperature rise. We also show the impact of temperature changes on discomfort perceptions and avoidance behavior. More specifically, when temperature increases, the time spent in store decreases, but less proportionally than actual temperature rise when we get out of the range of comfort. These results confirm psychophysical and ergonomics hypotheses.nonouirechercheNationa