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The complexity of algorithmic teaching, query learning, and sample compression

IHP Salle 314

Computational learning theory is concerned with the complexityof machine learning problems, for instance with the question ofhow many training examples are needed for a machine toidentify a concept in a given class of possible target concepts.   This presentation focuses on the combinatorial structureof concept classes that can be learned from a small number ofexamples. When learning from randomly chosen examples, theVC-dimension is known to provide bounds on the numberof examples needed for learning. However, for previously studiedmodels of algorithmic teaching (i.e., learning from helpfulexamples), no such combinatorial parameters are […]

Information-based complexity of black-box convex optimization: a new look via feedback information theory

IHP Salle 314

In this talk, I will revisit information complexity of black-box convex optimization, first studied in the seminal work of Nemirovski and Yudin, from the perspective of feedback information theory. These days, large-scale convex programming arises in a variety of applications, and it is important to refine our understanding of its fundamental limitations. The goal of black-box convex optimization is to minimize an unknown convex objective function from a given class over a compact, convex domain using an iterative scheme that generates approximate solutions by querying an oracle for local information […]

Global dynamics beyond the ground energy for the nonlinear Klein-Gordon equation

Chevaleret

We study global behavior of the nonlinear Klein-Gordon equation with a focusing cubic power in three dimensions, in the energy space under the restriction of radial symmetry and an energy upper bound slightly above that of the ground state. We give a complete classification of the solutions into 9 non-empty sets according to whether they blow-up, scatter to 0, or scatter to the ground states, in the forward and backward time directions, and the splitting is given in terms of the stable and the unstable manifoldsof the ground states. This […]

Quasistatic crack growth in finite elasticity

Chevaleret

We present a variational model for quasistatic evolutions of brittle cracks in hyperelastic bodies, in the context of finite elasticity.All existence results on this subject that can be found in the mathematical literature were obtained using energy densities with polynomial growth. This is not compatible with the standard assumption in finite elasticity that the strain energy diverges as the determinant of the deformation gradient tends to zero. On the contrary, we consider a wide class of energy densities satisfying this property

Grandes matrices aléatoires

ENS (amphithéâtre Galois sous la bibliothèque de mathématique)

L'exposé présentera un petit panorama autour de l'asymptotique de matrices aléatoires dont la taille croît vers l'infini, à la fois au niveau de la mesure spectrale et du comportement individuel des valeurs propres (valeurs propres extrêmes, espacements...). Les théorèmes récents d'universalité au bord et à l'intérieur du spectre seront évoqués.

Montée et redescente au dessus des surfaces de Châtelet

Salle W

Les torseurs versels ont été introduits par J.-L. Colliot-Thélène et J.-J. Sansuc pour étudier le principe de Hasse et l'approximation faible sur des variétés telles que les surfaces de Châtelet. Dans un travail avec Tim Browning et Régis de la Bretèche, nous avons utilisé ces torseurs comme première étape pour démontrer le principe de Batyrev et Manin pour certaines de ces surfaces. Le but de cet exposé est de présentercette étape de la preuve.

Zeros of p-adic forms

Salle W

Artin conjectured that any form of degree d over a p-adic field should have a non-trivial zero as soon as the number of variables exceeds d2. There are related statements for systems of forms.The talk will give a review of Artin's conjecture, with particular emphasis on recent workconcerning systems of quadratic forms.