Representations admitting two pairs of supplementary invariant spaces

We examine the lattice generated by two pairs of supplementary vector subspaces of a finite-dimensional vector space by intersection and sum, with the aim of applying the results to the study of representations admitting two pairs of supplementary invariant spaces, or one pair and a reflexive form. We show that such a representation is a direct sum of three canonical sub-representations which we characterize. We then focus on holonomy representations with the same property

The Noncommutative Constraints on the Standard Model \`a la Connes

Noncommutative geometry applied to the standard model of electroweak and strong interactions was shown to produce fuzzy relations among masses and gauge couplings. We refine these relations and show then that they are exhaustive.Comment: 12 pages LaTeX, 4 figure

NPEFix: Automatic Runtime Repair of Null Pointer Exceptions in Java

Null pointer exceptions, also known as null dereferences are the number one exceptions in the field. In this paper, we propose 9 alternative execution semantics when a null pointer exception is about to happen. We implement those alternative execution strategies using code transformation in a tool called NPEfix. We evaluate our prototype implementation on 11 field null dereference bugs and 519 seeded failures and show that NPEfix is able to repair at runtime 10/11 and 318/519 failures

The optimal contract under adverse selection in a moral-hazard model with a risk-averse agent

This paper studies the optimal contract offered by a risk-neutral principal to a risk-averse agent when the agent’s hidden efficiency and action both improve the probability of the project being successful. We show that if the agent is sufficiently prudent and efficient, the principal induces a higher probability of success than under moral hazard, despite the costly informational rent given up. Moreover, the conditions to avoid pooling are difficult to satisfy because of the different kinds of incentives to be managed and the overall trade-off between rent extraction, insurance, and efficiency involved

Les marchés à tranches

Cet article étudie les marchés publics à tranches. Ces procédures sont caractérisées par la présence d'une incertitude sur la réalisation complète d'une opération. Celle-ci est alors découpée en plusieurs travaux (tranches) qui doivent être réalisés successivement. La première tranche est effectuée juste après l'attribution du marché, tandis que l'affermissement des suivantes est soumis à la réalisation de certaines conditions prévues par le contrat. Les règles optimales d'approvisionnement sont déterminées pour deux tranches. On montre que la firme la plus efficace exante gagne le marché. Mais l'incertitude fait qu'elle ne l'est plus nécessairement ex-post. Nous évaluons par la suite le coût de l'incertitude lié au risque d'une allocation inefficace ex-post.Marchés publics, tranches

Multirhythmicity in an optoelectronic oscillator with large delay

An optoelectronic oscillator exhibiting a large delay in its feedback loop is studied both experimentally and theoretically. We show that multiple square-wave oscillations may coexist for the same values of the parameters (multirhythmicity). Depending on the sign of the phase shift, these regimes admit either periods close to an integer fraction of the delay or periods close to an odd integer fraction of twice the delay. These periodic solutions emerge from successive Hopf bifurcation points and stabilize at a finite amplitude following a scenario similar to Eckhaus instability in spatially extended systems. We find quantitative agreements between experiments and numerical simulations. The linear stability of the square-waves is substantiated analytically by determining stable fixed points of a map.Comment: 14 pages, 7 figure

Quelques constats sur les prévisions conjoncturelles de la croissance française

We study the quality of the French growth forecasts from the first decade of the century. An optimism bias of the quarterly Consensus growth forecasts can be asserted right from a graphic analysis and its existence is confirmed by the calculation of the mean errors which are systematically negative. The Theil index reveals that Insee forecasts are superior to the Consensus ones. In addition, the Consensus forecasts are superior to a naïve forecast. Proper tests seem to confirm that an optimism bias exists ; this bias could arise from the combination of several forecasts. The study of the Consensus Economics fixed event forecasts regarding the next coming year requires a preliminary analysis due to missing data. We thus only retain the forecasts of nine institutions that we compare to those of the Government, the IMF, the OECD, and the European Commission. It appears that the forecasts are fairly close to the Consensus forecast and that the optimism bias is still observable. Finally, the disagreement between the forecasters increases towards a recession and, then, decreases.Nous étudions la qualité des prévisions de croissance pour la France réalisées durant la première décennie de ce siècle. Un biais d'optimisme des prévisions Consensus de la croissance trimestrielle apparaît dès l'examen graphique, et son existence est confirmée par le calcul des moyennes des erreurs de prévisions qui sont systématiquement négatives. L'indicateur de Theil montre que les prévisions de l'Insee dominent celles du Consensus qui obtiennent de meilleurs résultats qu'une prévision naïve (donnée par le dernier taux de croissance connu). Les tests semblent confirmer la présence d'un biais d'optimisme dans les prévisions trimestrielles, biais qui peut provenir dans le cas des prévisions Consensus de l'agrégation des prévisions collectées par le Consensus Economics. L'étude des prévisions de croissance pour l'année à venir faites par chaque organisme interrogé mensuellement par le Consensus Economics nécessite un traitement préalable à cause des données manquantes. Au final nous ne retenons que les prévisions de neuf institutions que nous comparons avec celles du gouvernement, du FMI, de l'OCDE, et de la Commission Européenne. Il apparait d'une part que les prévisions sont très proches de la prévision Consensus, et d'autre part que le biais d'optimisme reste présent. Enfin, le désaccord entre les institutions s'accroît à l'approche d'une phase de contraction et décroît après

Ambiguity, Optimism, and Pessimism in Adverse Selection Models

We investigate the effect of ambiguity and ambiguity attitude on the shape and properties of the optimal contract in an adverse selection model with a continuum of types, using the parametric model of ambiguity and ambiguity aversion called the NEO-additive model (Chateauneuf, Eichberger, and Grant, 2007). We show that it necessarily features efficiency and a jump at the top and pooling at the bottom of the distribution. Conditional on the degree of ambiguity, the pooling section may or may not be supplemented by a separating section. As a result, ambiguity adversely affects the principal’s ability to solve the adverse selection problem and therefore the least efficient types benefit from ambiguity with respect to risk. Conversely, ambiguity is detrimental to the most efficient types. This is confirmed in the comparative statics section