Désingularisation de métriques d’Einstein. I

We find a new obstruction for a real Einstein 4-orbifold with an A ₁-singularity to be a limit of smooth Einstein 4-manifolds. The obstruction is a curvature condition at the singular point. For asymptotically hyperbolic metrics, with boundary at infinity a conformal metric, we prove that if the obstruction vanishes, one can desingularize Einstein orbifolds with such singularities. The Dirichlet problem consists in finding Einstein metrics with given conformal infinity on the boundary: we prove that our obstruction defines a wall in the space of conformal metrics on the boundary, and that all the Einstein metrics must have their conformal infinity on one side of the wall.     

Construction dʼopérades ensemblistes à partir de monoïdes

We study a functorial construction from the category of monoids to the category of set-operads and we give some combinatorial examples of applications.     

Tests dʼadéquation à la mesure de Haar,identité de duplication de Watson et représentations dʼun groupe compact

We use the theory of compact groups representations in building goodness-of-fit tests for the Haar probability measure. An interpretation of a duplication identity already known for the celebrated circular test of G. Watson is given in terms of representation theory.     

Les fonctions métriques fondamentales dans un espace de plusieurs dimensions et de courbure constante

Sans résumé     

Calcul de lʼespérance de la solution dʼune EDP stochastique unidimensionnelle à lʼaide dʼune base réduite

In this Note, we present an efficient method to approximate the expectation of the response of a one-dimensional elliptic problem with stochastic inputs. In conventional methods, the computational effort and cost of the approximation of the response can be dramatic. Our method presented here is based on the Karhunen–Loève (K-L) expansion of the inverse of the diffusion parameter, allowing us to build a base of random variables in reduced numbers, from which we construct a projected solution. We show that the expectation of this projected solution is a good approximation, and give an a priori error estimate. A numerical example is presented to show the efficiency of this approach.     

Plans dʼexpérience pour lʼestimation de la courbe de concentration et de lʼAUC

The problem of interest is to estimate the concentration curve and the area under the curve (AUC) by estimating the parameters of a linear regression model with autocorrelated error process. We introduce a simple linear nonparametric unbiased estimator of the concentration curve and the AUC. We show that this estimator constructed from an appropriate regular sampling design is asymptotically optimal.     

Une méthode de décomposition en temps avec des schémas dʼintégration réversible pour la résolution de système dʼéquations différentielles ordinaires

We propose a time domain decomposition method that breaks the sequentiality of the integration scheme for systems of ODE. Under the condition of differentiability of the flow, we transform the initial value problem into a well-posed boundary values problem using the symmetrization of the interval of time integration and time-reversible integration scheme. For systems of linear ODE, we explicitly construct the block tridiagonal system satisfied by the solutions at the time sub-intervals extremities. We then propose an iterative algorithm of Schwarz type for updating the interfaces conditions which can extend the method to systems of nonlinear ODE.     

Estimation par le minimum de distance de Hellinger dʼun processus ARFIMA

In this Note, we determine the minimum Hellinger distance estimate of an ARFIMA (AutoRegressive Fractionally Integrated Moving Average) process. The estimate minimizes the Hellinger distance between the probability density function of the innovation of the process and a parameterized random function. Under some assumptions, we establish the asymptotic properties of this estimate.     

Sur lʼusage de la formule de Cauchy–Binet dans les démonstrations de convergence de lʼalgorithme QR tri-diagonal avec décalages

Using the Cauchy–Binet formula, one shows that it is possible to simplify the convergence proofs of the tridiagonal QR algorithm with shifts due to Wilkinson (1968) [12], Hoffmann–Parlett (1978, 1998) [3], [7], and Jiang–Zhang (1985) [4], including the quadratic or cubic convergence results.     

Variétés anti-de Sitter de dimension 3 possédant un champ de Killing non trivial

The aim of this Note is to find all compact 3-dimensional anti-de Sitter manifolds admitting a non-trivial Killing field.     

La signature basique est un invariant dʼhomotopie feuilletée

We prove that the basic signature of a homologically orientable Riemannian foliation with even codimension, is a foliated homotopy invariant.