Institut de Mathématiques de Toulouse

Agenda



Séminaires


  • Algèbre, Dynamique et Topologie


    • Mardi 27 février 11:00-12:00 -

      Pas de Séminaire de Géométrie et Topologie

      [Séminaire]


    • Mardi 6 mars 11:00-12:00 - José Andrés Rodriguez Migueles

      TBA

      [Séminaire]


    • Mardi 3 avril 11:00-12:00 - Genevieve Walsh

      Séminaire de Géométrie et Topologie

      [Séminaire]


    • Mardi 17 avril 11:00-12:00 -

      Pas de Séminaire de Géométrie et Topologie

      [Séminaire]


    • Mardi 22 mai 11:00-12:00 - Maxime Wolff

      Séminaire de Géométrie et Topologie

      Lieu : Salle Pellos (1R1, 207)

      [Séminaire]


  • Géométrie algébrique, champs et homotopie


    • Mardi 13 mars 14:00-15:00 - B. Toën - IMT

      Espaces de modules de connexions

      Résumé : On présente un énoncé de représentabilité pour le problème de modules des connexions sur une variété non-nécessairement compacte. On tente de se convaincre que l’espace des modules correspondant est muni d’une structure de Poisson (avec décalage).

      [Séminaire]


    • Mardi 27 mars 14:00-15:00 - Marcello Bernardara - IMT

      TBA

      [Séminaire]


    • Mardi 3 avril 14:00-15:00 - Olivier Schiffmann - Orsay

      TBA

      [Séminaire]


    • Mardi 24 avril 14:00-15:00 - Frédéric Déglise - CNRS, Univ. Dijon

      TBA

      [Séminaire]


    • Mardi 15 mai 14:00-15:00 - Grégory Ginot - IMJ, Paris 13

      TBA

      [Séminaire]


    • Mardi 19 juin 14:00-15:00 - Jonathan Block - UPenn

      TBA

      [Séminaire]


    • Mardi 26 juin 14:00-15:00 - Guiseppe Ancona - IRMA (Strasbourg)

      TBA

      [Séminaire]


  • Séminaire de l équipe MIP


    • Mardi 20 février 11:00-12:00 - Ayman Moussa - LJLL, Université Pierre et Marie Curie

      Uniqueness of weak solutions for the 2D Vlasov-Navier-Stokes system.

      Résumé : We prove a uniqueness result for weak solutions to the Vlasov-Navier-Stokes system in two dimensions, both in the whole space and in the periodic case, under a mild decay condition on the initial distribution function. The main result is achieved by combining methods from optimal transportation (introduced in this context by G. Loeper) with the use of Hardy’s maximal function, in order to obtain some fine Wassestein-like estimates for the difference of two solutions of the Vlasov equation.

      Lieu : Salle MIP

      [Séminaire]


    • Mardi 27 février 11:00-12:00 - Pas de séminaire

      [Séminaire]


    • Mardi 6 mars 11:00-12:00 - Frédéric Rousset - Université Paris-Sud

      Titre et résumé à préciser

      Lieu : Salle MIP

      [Séminaire]


    • Mardi 13 mars 11:00-12:00 - Masahito Ohta - Tokyo University of Science

      Strong instability of standing waves for nonlinear Schrödinger equations with a partial confinement

      Résumé : We study the instability of standing wave solutions for nonlinear Schr\"odinger equations with a one-dimensional harmonic potential in dimension N greater than or equal to 2. We prove that if the nonlinearity is L^2-critical or supercritical in dimension N-1, then any ground-state standing waves are strongly unstable by blowup, that is,
      there exist finite time blowup solutions with initial data arbitrarily close to the standing waves. This shows that the upper bound of the nonlinearity in Bellazzini, Boussa\"id, Jeanjean and Visciglia (2017) is optimal for the existence of stable standing waves.

      Lieu : Salle MIP

      [Séminaire]


    • Mardi 20 mars 11:00-12:00 - Nicolas Seguin - Université de Rennes 1

      Titre et résumé à venir

      [Séminaire]


    • Mardi 27 mars 11:00-12:00 - Luis Vega - Departamento de Matematicas, Universidad del Pais Vasco/EHU

      A venir

      Lieu : Salle MIP

      [Séminaire]


    • Mardi 3 avril 11:00-12:00 - Nicolas Burq - Université d'Orsay

      Titre et résumé à venir

      [Séminaire]


    • Mardi 10 avril 11:00-12:00 - Michael Goldman - Université Paris Diderot, LJLL

      A variational approach to regularity theory for the Monge-Ampere equation

      Résumé : In this talk I will present a new proof of the partial regularity of optimal transport maps. As opposed to the previous proof of Figalli and Kim which was using Caffarelli’s approach to regularity of solutions of Monge-Ampere equations via maximum principles arguments, our proof is variational in nature. By using the fluid-dynamic formulation of optimal transportation (which usually goes by the name of Benamou-Brenier formulation) we prove that at every scale, the optimal transport map is close to the gradient of an harmonic function. This allows us to set up a Campanato iteration scheme to obtain the desired regularity. This is joint work with F. Otto.

      Lieu : Salle MIP

      [Séminaire]


    • Mardi 17 avril 11:00-12:00 - Pas de séminaire

      [Séminaire]


    • Mardi 24 avril 11:00-12:00 - Evelyne Miot - Université de Grenoble

      Séminaire MIP

      [Séminaire]

0 | 10

  • Séminaire de Probabilités


    • Mardi 20 février 09:45-10:45 - Michal Sztrelecki - University of Warsaw

      Convex log-Sobolev inequalites on the real line

      Résumé : I shall explain how one can characterize those measures on the real line which satisfy the log-Sobolev inequality for convex functions (and also : how this problem is related to the theory of weak transport-entropy inequalities). As a consequence, we will be able to obtain dimension-free concentration bounds for the lower and upper tails of convex functions of independent random variables which satisfy the convex log-Sobolev inequality. The talk will be based on joint work with Yan Shu.

      [Séminaire]


    • Mardi 6 mars 09:45-10:45 - Aline Marguet - Ecole Polytechnique

      Séminaire de Probabilités

      [Séminaire]


    • Mardi 13 mars 09:45-10:45 - Mathias Rousset - INRIA Rennes

      Séminaire de Probabilités

      [Séminaire]


    • Mardi 20 mars 09:45-10:45 - Martin Huesmann - University of Bonn

      Séminaire de Probabilités

      [Séminaire]


    • Mardi 3 avril 09:45-10:45 - Vincent Tassion - ETH Zurich

      Séminaire de Probabilités

      [Séminaire]


    • Mardi 10 avril 09:45-10:45 - James Norris - University of Cambridge

      Séminaire de Probabilités

      [Séminaire]


    • Mardi 15 mai 09:45-10:45 - Tony Lelievre - ENPC

      Séminaire de Probabilités

      Résumé : Seminaire commun avec MIP

      [Séminaire]


    • Mardi 29 mai 09:45-10:45 - Tania Kosentkova - Universitat Potsdam

      Séminaire de Probabilités

      Lieu : Amphi Schwartz

      [Séminaire]


    • Mardi 5 juin 09:45-10:45 - Beatrice de Tiliere - Universite Paris-Est Creteil

      Séminaire de Probabilités

      Lieu : Amphi Schwartz

      [Séminaire]


    • Mardi 12 juin 09:45-10:45 - Raphael Chétrite - CNRS et Université de Nice

      Séminaire de Probabilités

      [Séminaire]


  • Séminaire de Statistique


    • Mardi 6 mars 11:00 - Jérôme Morio - Onera Toulouse

      Reliability-based sensitivity estimators of rare event probability in the presence of distribution parameter uncertainty

      Résumé : This paper aims at presenting sensitivity estimators of a rare event probability in the context of uncertain distribution
      parameters (which are often not known precisely or poorly estimated due to limited data). Since the distribution parameters
      are also affected by uncertainties, a possible solution consists in considering a second probabilistic uncertainty level. Then,
      by propagating this bi-level uncertainty, the failure probability becomes a random variable and one can use the mean
      estimator of the distribution of the failure probabilities (i.e. the “predictive failure probability”, PFP) as a new measure of
      safety. In this paper, the use of an augmented framework (composed of both basic variables and their probability distribution
      parameters) coupled with an Adaptive Importance Sampling strategy is proposed to get an efficient estimation strategy of the
      PFP. Consequently, double-loop procedure is avoided and the computational cost is decreased. Thus, sensitivity estimators
      of the PFP are derived with respect to some deterministic hyper-parameters parametrizing a priori modeling choice.

      Lieu : Salle 106, Bat 1R1

      [Séminaire]


    • Mardi 13 mars 11:00-12:00 - Fabrice Gamboa - IMT

      Approximate Optimal Designs for Multivariate Polynomial Regression

      Résumé : We introduce a new approach aiming at computing approximate optimal designs for multivariate polynomial regressions on compact (semi-algebraic) design spaces. We use the moment-sum-of-squares hierarchy of semidefinite programming problems to solve numerically the approximate optimal design problem. The geometry of the design is recovered via semidefinite programming duality theory. This work shows that the hierarchy converges to the approximate optimal design as the order of the hierarchy increases. Furthermore, we provide a dual certificate ensuring finite convergence of the hierarchy and showing that the approximate optimal design can be computed numerically with our method. As a byproduct, we revisit the equivalence theorem of the experimental design theory : it is linked to the Christoffel polynomial and it characterizes finite convergence of the moment-sum-of-square hierarchies.

      Lieu : Salle 106 1R1

      [Séminaire]


    • Mardi 27 mars 11:00-12:00 - Guillaume Lecué - CREST

      Robust machine learning by median-of-means : theory and practice

      Résumé : We introduce new estimators of least-squares minimizers based on median-of-means (MOM) estimators of the mean of real valued random variables. These estimators achieve optimal rates of convergence under minimal assumptions on the dataset. The dataset may also have been corrupted by outliers on which no assumption is granted. We also analyze these new estimators with standard tools from robust statistics. In particular, we revisit the concept of breakdown point. We modify the original definition by studying the number of outliers that a dataset can contain without deteriorating the estimation properties of a given estimator. This new notion of breakdown number, that takes into account the statistical performances of the estimators, is non-asymptotic in nature and adapted for machine learning purposes. We proved that the breakdown number of our estimator is of the order of (number of observations) * (rate of convergence). For instance, the breakdown number of our estimators for the problem of estimation of a d-dimensional vector with a noise variance sigma^2 is sigma^2d and it becomes sigma^2 s \log(ed/s) when this vector has only s non-zero component. Beyond this breakdown point, we proved that the rate of convergence achieved by our estimator is (number of outliers divided by (number of observations).
      Besides these theoretical guarantees, the major improvement brought by these new estimators is that they are easily computable in practice and are therefore well suited for robust machine learning. In fact, basically any algorithm used to approximate the standard Empirical Risk Minimizer (or its regularized versions) has a robust version approximating our estimators. On top of being robust to outliers, the ``MOM version" of the algorithms are even faster than the original ones, less demanding in memory resources in some situations and well adapted for distributed datasets which makes it particularly attractive for large dataset analysis. As a proof of concept, we study many algorithms for the classical LASSO estimator. It turns out that a first version of our algorithm can be improved a lot in practice by randomizing the blocks on which ``local means" are computed at each step of the descent algorithm. A byproduct of this modification is that our algorithms come with a measure of depth of data that can be used to detect outliers, which is another major issue in Machine learning.

      Lieu : Salle 106 1R1

      [Séminaire]


  • Systèmes dynamiques


    • Vendredi 23 février 10:30-11:30 - Nguyen Tien Zung - IMT

      Une approche conceptuelle au problème de variables action-angle

      Résumé : Je vais expliquer une "nouvelle sorte de lois de conservation"
      à partir de laquelle on obtient facilement les variables action-angle
      pour les systèmes intégrables classiques, mais aussi d’autres formes
      normales intéressantes pour d’autres types de systèmes dynamiques.
      (e.g., systèmes sur les variétés de Dirac, système aux voisinages de
      singularités, systèmes stochastiques, etc.)
      Cet exposé est basé sur l’article arXiv:1706.08859
      (43 pages, Archive for Rational Mechanics and Analysis 2018)

      Lieu : salle 207, bat 1R2

      [Séminaire]


    • Vendredi 16 mars 10:30-11:30 - Cristobal Rojas - Universidad Andrés Bello, Santiago, Chile

      A préciser

      Lieu : salle 207, bat 1R2

      [Séminaire]


    • Vendredi 30 mars 10:30-11:30 - Beatriz Molina - Université de Valladolid

      Newton non-degenerate foliations

      Résumé : We introduce the concept of Newton non-degenerate foliations and we prove that they are exactly those that have a combinatorial reduction of singularities (toric type foliations). We do it through the Newton polyhedra system of the foliation.

      Lieu : salle 207, bat 1R2

      [Séminaire]


    • Vendredi 13 avril 10:30-11:30 - Valente Ramirez - Cornell University

      The spectra of singularities of quadratic vector fields

      Résumé : Consider a polynomial vector field of degree $n \geq 2$ on $C^2$. In the generic case, it has $n^2$ isolated singularities, and the holomorphic foliation it defines on $P^2$ has an invariant line at infinity with $n+1$ singular points.

      Lieu : salle 207, bat 1R2

      [Séminaire]


    • Vendredi 15 juin 10:30-11:30 - Loic Teyssier - IRMA, Strasbourg

      A préciser

      Lieu : salle 207, bat 1R2

      [Séminaire]


  • Mathématiques pour la biologie


    • Jeudi 22 février 13:30-14:30 - Antoine Wystrach - CRCA (Toulouse)

      The emergence of navigational behaviour in insects

      Résumé : Navigation requires the coordination between different type of actions
      (e.g., choosing a direction, going forward etc…), and the control
      mechanisms that ‘triggers’ these actions is often characterised as decision
      making. Here we will see that distinct behaviour can spontaneously emerge
      from simple, continuous processes without the need to ‘trigger’ or ‘select’
      actions. We will see that such non-reducible, distributed processes
      emerging from the interaction between brain, body and environment can
      provide robust and generalist solutions to various and apparently different
      navigational tasks.

      Lieu : salle MIP, 1er étage bat 1R3

      [Séminaire]


    • Jeudi 15 mars 13:30-14:30 - Thomas Lepoutre - INRIA Rhône Alpes

      Mathematical models for chronic myeloid leukemia

      Résumé : Chronic myeloid leukemia has been drastically changed by the introduction of targeted therapies in the 2000s. Currently, one of the challenging question is how to decide wether one can stop therapy or not. We will see how our models can give insights on the underlying mechanisms responsible for success or failure of treatment cessation. We will especially discuss the hypothesis of an important role of the immune system in this result and how one can analyze then treatment free remission as a stability property. We will also review how some different models suggest the patients might be overtreated.

      Lieu : salle MIP, 1er étage bat 1R3

      [Séminaire]


    • Jeudi 29 mars 13:30-14:30 - Rémi Servien - INRA - Ecole Nationale Vétérinaire de Toulouse

      TBA

      Lieu : salle MIP, 1er étage bat 1R3

      [Séminaire]


    • Jeudi 12 avril 13:30-14:30 - Diala Abu Awad - INRA Montpellier

      TBA

      Lieu : salle MIP, 1er étage bat 1R3

      [Séminaire]


    • Jeudi 26 avril 13:30-14:30 - Maxime Breden - TU Munich

      TBA

      Lieu : salle MIP, 1er étage bat 1R3

      [Séminaire]


    • Jeudi 17 mai 13:30-14:30 -

      TBA

      Lieu : salle MIP, 1er étage bat 1R3

      [Séminaire]


    • Jeudi 31 mai 13:30-14:30 - Clément Sire - LPT, IRSAMC

      (Measuring) Social Interactions and (Studying) Collective States in Fish Schools

      Résumé : The flexible coordination of individuals’ movements ensures rapid and coherent changes in direction of travel of fish schools for instance as a reaction to a predator detected in the neighborhood. However the ’microscopic level’ interaction rules involved in the coordination of fish movements and the adapted collective response of a school still remain to a large extent unknown. Knowing such interaction rules could offer new sources of inspiration to design distributed control algorithms for swarms of drones. Here we present a systematic methodology to measure and analyze social interactions controlling the collective motion of animal groups. Contrary to classical forces between physical objects, social interactions between individuals explicitly depend on their relative headings and are affected by their anisotropic and asymmetric perception of their environment. Hence they strongly break the Newtonian’s law of action-reaction. When applied to fish groups, this approach leads to the quantitative measurement of the spontaneous behavior of a fish, of its avoidance interaction with the tank walls, and of its attraction and alignment interaction with another fish. We use the results of this analysis to build an explicit and faithful model that convincingly reproduces quantitative and qualitative features of the actual fish dynamics. We also show that the type of models derived from such analysis reproduces the main collective states observed in actual fish schools, when one varies the intensity of the alignment and attraction interactions between fish.

      [Séminaire]


    • Jeudi 14 juin 13:30-14:30 - Philippe Saint-Pierre - IMT

      TBA

      Lieu : salle 106 1er étage bat 1R1

      Notes de dernières minutes : Attention, changement de salle : salle 106 1er étage bat 1R1

      [Séminaire]



  • Géométrie Complexe


    • Vendredi 9 mars 09:00-10:00 - Tim Kirschner - Universität Duisburg-Essen

      Group actions on holomorphic Lagrangian fibrations

      Résumé : Let $n$ be a natural number, $G$ be a finite subgroup of the general linear group of degree $n$, and $B$ be an open neighborhood of the origin in $\mathbb C^n$ on which $G$ acts by matrix multiplication. Moreover, let $f \colon (X,\sigma) \to B$ be a holomorphic Lagrangian fibration and assume that we are given a holomorphic symplectic action of $G$ on $(X,\sigma)$ which makes the map $f$ equivariant.
      In my talk I ask : When the action of $G$ on $X$ is fixed point free, so that we can form the quotient $X/G$ as a complex manifold, what can we say about $G$ ? If $n=1$, for instance, the group $G$ is necessarily trivial. I will present partial results for $n>1$ and explain how these can be applied to study the singularities of base spaces of fibrations on irreducible holomorphic symplectic manifolds.

      [Séminaire]


    • Vendredi 16 mars 09:00-10:00 - Lionel Darondeau - KU Leuven

      Hyperbolicité des paires orbifoldes géométriques

      Résumé : Je vais présenter un travail en cours avec F. Campana et E. Rousseau sur l’hyperbolicité des paires orbifoldes. Je rappelerai tout d’abord la notion de courbe entière dans la catégorie des orbifoldes géométriques introduite par Campana. Je justifierai brièvement la nécessité de travailler dans ce cadre, qui généralise et étend le cadre classique (cadre compact et cadre logarithmique). Nous verrons ensuite que la théorie naturelle des différentielles de jets orbifoldes (que nous introduisons en degrés supérieurs) réserve quelques surprises, en rupture avec le cadre classique.

      [Séminaire]


    • Vendredi 16 mars 10:30-11:30 - David Witt Nyström - Chalmers University

      TBA

      [Séminaire]


    • Vendredi 30 mars 09:00-11:30 - Hoang Chinh Lu - Orsay

      Propriétés de concavité du volume

      Résumé : Travail en commun avec T.Darvas et E.Dinezza.

      [Séminaire]


    • Vendredi 30 mars 14:30-17:00 - Tat Dat To - IMT

      Théorie du pluripotentiel sur les variétés hermitiennes

      Résumé : D’après Dinew-Kolodziej et Kolodziej-Nguyen.

      [Séminaire]


    • Vendredi 6 avril 09:00-10:00 - Erwan Rousseau - Université Aix-Marseille

      TBA

      [Séminaire]


    • Vendredi 13 avril 09:00-10:00 - Ruadhai Dervan - Cambridge / Ecole Polytechnique

      TBA

      [Séminaire]


    • Vendredi 27 avril 09:00-10:00 - Stéphane Druel - Université Grenoble Alpes

      TBA

      [Séminaire]


    • Vendredi 4 mai - Pas d'exposé cette semaine

      Workshop "Semiorthogonal decompositions, stability conditions and sheaves of categories"

      [Séminaire]


    • Vendredi 11 mai 09:00-10:00 - Christophe Mourougane - Université Rennes 1

      TBA

      [Séminaire]

0 | 10

Groupes de Travail


  • Probabilités et statistique


    • Jeudi 3 mai 12:30-13:30 - Fabien Panloup - LAREMA, Université d'Angers

      TBA

      Lieu : Room 106, building 1R1, UPS.

      [Séminaire]



    • Mardi 6 mars 14:00-15:00 - Leyth Akrout - IMT

      Homologie de Hochschild 1

      [Séminaire]


    • Mardi 13 mars 15:30-16:30 - Leyth Akrout - IMT

      Homologie de Hochschild 2

      [Séminaire]


    • Mardi 20 mars 14:00-15:00 - Massimo Pippi - IMT

      Théorème HKR 1

      [Séminaire]


    • Mardi 27 mars 15:30-16:30 - Massimo Pippi - IMT

      Théorème HKR 2

      [Séminaire]



Evénement Important




  • Colloquium de l IMT