The OS* Algorithm: a Joint Approach to Exact Optimization and Sampling

Most current sampling algorithms for high-dimensional distributions are based on MCMC techniques and are approximate in the sense that they are valid only asymptotically. Rejection sampling, on the other hand, produces valid samples, but is unrealistically slow in high-dimension spaces. The OS* algorithm that we propose is a unified approach to exact optimization and sampling, based on incremental refinements of a functional upper bound, which combines ideas of adaptive rejection sampling and of A* optimization search. We show that the choice of the refinement can be done in a way that ensures tractability in high-dimension spaces, and we present first experiments in two different settings: inference in high-order HMMs and in large discrete graphical models.Comment: 21 page

A different kind of activism: the position of catholic women teachers in their union (Belgium, 1950-1965)

In this article we would like to focus on the position of women in the Christian teachers union in Belgium in the years 1950-1965. In spite of their numerical dominance in the teaching occupation and in the union, women teachers never exercised real structural power in teacher unionism during this period. Yet, the union was alive to the fact that women teachers formed an important segment of their members. The marriage bar f.e. became a central issue in the debate concerning the legal statute of the catholic teachers in the years 1961-1963. Based on primary sources, interviews, national and international literature, we will focus on the apparent lack of female militantism by situating it in its social and historical context and by analysing the prevailing ideology concerning labour and the family.("Un activisme différent. Les prises de position des institutrices catholiques au sein de leur syndicat. Belgique, 1950-1965") Dans cet article nous voudrions nous centrer sur la position des femmes appartenant au syndicat des enseignants chrétien en Belgique durant les années 1950-1965. Malgré leur prédominance numérique dans l'enseignement fondamental et dans l'union, les institutrices n'ont jamais exercé une vraie puissance structurelle dans leur syndicat d'enseignants pendant cette période. Cependant, l'union était très active du fait que les institutrices représentaient une section importante de leurs membres. Le bannissement du mariage, p.e., devint une question cruciale au cours de la discussion portant sur le statut légal des professeurs catholiques dans les années 1961-1963. Nous basant sur des sources primaires, des entrevues et l'historiographie nationale et internationale, nous nous concentrerons sur le manque apparent de militantisme féminin en le replaçant dans son contexte social et historique et en analysant l'idéologie dominante au sujet du travail et de la famille

Solving Polynomial Systems via a Stabilized Representation of Quotient Algebras

We consider the problem of finding the isolated common roots of a set of polynomial functions defining a zero-dimensional ideal I in a ring R of polynomials over C. We propose a general algebraic framework to find the solutions and to compute the structure of the quotient ring R/I from the null space of a Macaulay-type matrix. The affine dense, affine sparse, homogeneous and multi-homogeneous cases are treated. In the presented framework, the concept of a border basis is generalized by relaxing the conditions on the set of basis elements. This allows for algorithms to adapt the choice of basis in order to enhance the numerical stability. We present such an algorithm and show numerical results

On uniqueness of static Einstein-Maxwell-dilaton black holes

We prove uniqueness of static, asymptotically flat spacetimes with non-degenerate black holes for three special cases of Einstein-Maxwell-dilaton theory: For the coupling ``$\alpha = 1$'' (which is the low energy limit of string theory) on the one hand, and for vanishing magnetic or vanishing electric field (but arbitrary coupling) on the other hand. Our work generalizes in a natural, but non-trivial way the uniqueness result obtained by Masood-ul-Alam who requires both $\alpha = 1$ and absence of magnetic fields, as well as relations between the mass and the charges. Moreover, we simplify Masood-ul-Alam's proof as we do not require any non-trivial extensions of Witten's positive mass theorem. We also obtain partial results on the uniqueness problem for general harmonic maps.Comment: LaTex, 24 pages, no figures; Corrected and enlarged versio

An easy computable upper bound for the price of an arithmetic Asian option.

Using some results from risk theory on stop-loss order and comonotone risks, we show in this paper that the price of an arithmetic Asian option can be bounded from above by the price of a portfolio of European call options.

Concentration of the Brownian bridge on Cartan-Hadamard manifolds with pinched negative sectional curvature

We study the rate of concentration of a Brownian bridge in time one around the corresponding geodesical segment on a Cartan-Hadamard manifold with pinched negative sectional curvature, when the distance between the two extremities tends to infinity. This improves on previous results by A. Eberle, and one of us. Along the way, we derive a new asymptotic estimate for the logarithmic derivative of the heat kernel on such manifolds, in bounded time and with one space parameter tending to infinity, which can be viewed as a counterpart to Bismut's asymptotic formula in small time