Organisateurs/Organizers

Henri Darmon (Université McGill)
Jean-François Coeurjolly (UQAM)


Archives

Colloque de mathématiques CRM-ISM
2018-2019
2017-2018
2016-2017
2015-2016
2014-2015
2013-2014
2012-2013
2011-2012
2010-2011
2009-2010
2008-2009
2007-2008
2006-2007
2005-2006
2004-2005
2003-2004
2002-2003

Colloque de statistique CRM-ISM-GERAD
2013-2014
2012-2013
2011-2012
2010-2011
2009-2010
2008-2009

2019 - 2020

Calendrier / Calendar

MONTRÉAL



Date Heure/Time : Le vendredi 30 août 2019 - 16:00

Lieu/Venue : UQAM, Pavillon Sherbrooke, 200, rue Sherbrooke ouest, salle SH-3620

Conférencier/Speaker : Ciprian Manolescu, UCLA - Chaire Aisenstadt 2019

Titre/Title : Khovanov homology, 3-manifolds, and 4-manifolds

Resume/Abstract :
Khovanov homology is an invariant of knots in R^3. A major open problem is to extend its definition to knots in other three-manifolds, and to understand its relation to surfaces in 4-manifolds. I will discuss some partial progress in these directions, from different perspectives (gauge theory, representation theory, sheaf theory). In the process I will also review some of the topological applications of Khovanov homology.


Date Heure/Time : Le vendredi 13 septembre 2019 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Brent Pym, McGill University

Titre/Title : Multiple zeta values in deformation quantization

Resume/Abstract :
The subject of "deformation quantization" originated as a mathematical abstraction of the passage from classical to quantum mechanics: starting from a classical phase space (i.e. a Poisson manifold), we deform the ordinary multiplication of functions to produce a noncommutative ring, which serves as the algebra of quantum observables.  Over the years, the theory has evolved from its physical origins to take on a mathematical life of its own, with rich connections to representation theory, topology, graph theory, number theory and more.  I will give an introduction to the subject and explain how the quantization process is inextricably linked, via a formula of Kontsevich, to special values of the Riemann zeta function, and their generalizations known as multiple zeta values.


Date Heure/Time : Le vendredi 20 septembre 2019 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Alex Lubotzky, The Hebrew University of Jerusalem

Titre/Title : Groups' approximation, stability and high dimensional expanders

Resume/Abstract :
Several well-known open questions (such as: are all groups sofic or hyperlinear?) have a common form: can all groups be approximated by asymptotic homomorphisms into the symmetric groups Sym(n) (in the sofic case) or the  unitary groups U(n) (in the hyperlinear case)?  In the case of U(n), the question can be asked with respect to different metrics and norms. We answer, for the first time, some of these versions, showing that there exist finitely presented groups which are not approximated by U(n) with respect to the Frobenius (=L_2)norm.   The strategy is via the notion of "stability": some higher dimensional  cohomology vanishing phenomena is proven to imply stability  and using   higher dimensional expanders, it is shown that some non-residually finite groups (central extensions of some lattices in p-adic Lie groups)  are Frobenious stable and hence cannot be Frobenius approximated.  All notions will be explained.  Based on joint works with M, De Chiffre, L. Glebsky and A. Thom and with I. Oppenheim. 


Date Heure/Time : Le jeudi 26 septembre 2019 - 16:00

Lieu/Venue : Université de Montréal, Pavillon Roger-Gaudry, salle M-415

Conférencier/Speaker : Nassif Ghoussoub, UBC - Lauréat 2019 du Prix CRM-Fields-PIMS

Titre/Title : From Monge optimal transports to optimal Skorokhod embeddings

Resume/Abstract :
The optimal transportation problem, which originated in the work of Gaspard Monge in 1781, provides a fundamental and quantitave way to measure the distance between probability distributions. It has led to many successful applications in PDEs, Geometry, Statistics and Probability Theory. Recently, and motivated by problems in Financial Mathematics, variations on this problem were introduced by requiring the transport plans to abide by certain "fairness rules," such as following martingale paths. One then specifies a stochastic state process and a costing procedure, and minimize the expected cost over stopping times with a given state distribution. Recent work has uncovered deep connections between this type of constrained optimal transportation problems, the celebrated Skorokhod embeddings of probability distributions in Brownian motion, and Hamilton-Jacobi variational inequalities.


Date Heure/Time : Le vendredi 4 octobre 2019 - 16:00

Lieu/Venue : CRM, Université de Montréal, Pavillon André-Aisenstadt, salle 1355

Conférencier/Speaker : Johanna Nešlehová, McGill University - Lauréate 2019 du Prix CRM-SSC

Titre/Title : La queue, la tuile, le bris d’égalité et leur rôle dans les modèles de dépendance 

Resume/Abstract :
La modélisation de la dépendance entre variables aléatoires est omniprésente en statistique. S’agissant d’événements rares à fort impact, tels que des orages violents, des inondations ou des vagues de chaleur, la question revêt une grande importance pour la gestion des risques et pose des défis théoriques. Une approche hautement flexible et prometteuse s’appuie sur la théorie des valeurs extrêmes, la modélisation par copules et l’inférence fondée sur les rangs. Je présenterai trois avancées récentes dans ce domaine. Nous nous intéresserons d’abord à la prise en compte de la dépendance en régime moyen, lorsque les modèles asymptotiques de valeurs extrêmes ne conviennent pas. Nous verrons ensuite quoi faire lorsque le nombre de variables est grand et comment une structure de modèle hiérarchique peut être apprise à partir de matrices de corrélation de rangs de grande taille. Enfin, je ne résisterai pas à l’envie de vous initier à l’univers complexe de l’inférence basée sur les rangs pour les données discrètes ou mixtes.


Date Heure/Time : Le vendredi 11 octobre 2019 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Ruth Misener, Imperial College

Titre/Title : Scoring positive semidefinite cutting planes for quadratic optimization via trained neural networks

Resume/Abstract :
Semidefinite programming relaxations complement polyhedral relaxations for quadratic optimization, but global optimization solvers built on polyhedral relaxations cannot fully exploit this advantage. We develop linear outer-approximations of semidefinite constraints that can be effectively integrated into global solvers for nonconvex quadratic optimization. The difference from previous work is that our proposed cuts are (i) sparser with respect to the number of nonzeros in the row and (ii) explicitly selected to improve the objective. A neural network estimator is key to our cut selection strategy: ranking each cut based on objective improvement involves solving a semidefinite optimization problem, but this is an expensive proposition at each Branch&Cut node. The neural network estimator, trained a priori of any instance to solve, takes the most time consuming computation offline by predicting the objective improvement for any cut. 


Date Heure/Time : Le vendredi 18 octobre 2019 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Jacob Tsimerman, University of Toronto

Titre/Title : o-minimal GAGA and applications to Hodge theory

Resume/Abstract :
(joint with B.Bakker and Y.Brunebarbe) One very fruitful way of studying complex algebraic varieties is by forgetting the underlying algebraic structure, and just thinking of them as complex analytic spaces. To this end, it is a natural and fruitful question to ask how much the complex analytic structure remembers. One very prominent result is Chows theorem, stating that any closed analytic subspace of projective space is in fact algebraic. One notable consequence of this result is that a compact complex analytic space admits at most 1 algebraic structure - a result which is false in the non-compact case. This was generalized and extended by Serre in his famous GAGA paper using the language of cohomology. We explain how we can extend Chow's theorem and in fact all of GAGA to the non-compact case by working with complex analytic structures that are "tame" in the precise sense defined by o-minimality. This leads to some very general "algebraization" theorems, and we give applications to Hodge theory.


Date Heure/Time : Le vendredi 25 octobre 2019 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Melanie Matchett Wood, UC Berkeley

Titre/Title : Coincidences in homological densities

Resume/Abstract :
For certain natural sequences of topological spaces, the kth homology group stabilizes once you go far enough out in the sequence of spaces. This phenomenon is called homological stability. Two classical examples of homological stability are the configuration space of n unordered distinct points in the plane, studied in the 60's by Arnold' and the space of (based) algebraic maps from CP^1 to CP^1 studied by Segal in the 70's. It turns out that the stable homology is the same in these two examples, and in this talk we explain that this is just the tip an iceberg--a subtle, but precise relationship between the values of stable of homology different sequences of spaces. To explain this relationship, which we discovered through an analogy to asymptotic counts in number theory, we introduce a new notion of homological density. This talk is on joint work with Benson Farb and Jesse Wolfson.


Date Heure/Time : Le vendredi 1 novembre 2019 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Stephen Walker, University of Texas

Titre/Title : General Bayesian modeling

Resume/Abstract :
The work is motivated by the inflexibility of Bayesian modeling; in that only parameters of probability models are required to be connected with data. The idea is to generalize this by allowing arbitrary unknowns to be connected with data via loss functions. An updating process is then detailed which can be viewed as arising in at least a couple of ways - one being purely axiomatically driven.   The further exploration of replacing probability model based approaches to inference with loss functions is ongoing. Joint work with Chris Holmes, Pier Giovanni Bissiri and Simon Lyddon.


Date Heure/Time : Le vendredi 8 novembre 2019 - 16:00

Lieu/Venue : CRM, Université de Montréal, Pavillon André-Aisenstadt, salle 6214

Conférencier/Speaker : Jaume Gomis, Lauréat 2019 du Prix CAP-CRM, Institut Périmètre de physique théorique

Titre/Title : Symmetries in topological quantum field theories

Resume/Abstract :
In this talk I will describe how to characterize symmetries of topological field theories and give a complete classification of symmetries in Abelian Topological Field Theories, uncovering a plethora of quantum symmetries in these theories and an intriguing connection to number theory


Date Heure/Time : Le vendredi 15 novembre 2019 - 16:00

Lieu/Venue : CRM, Université de Montréal, Pavillon André-Aisenstadt, salle 6214

Conférencier/Speaker : Yaniv Plan, University of British Columbia - Lauréat 2019 du Prix André-Aisnestadt

Titre/Title :

Resume/Abstract :
Random models lead to a precise and comprehensive theory of compressive sensing and matrix completion.  The number of random linear measurements needed to recover a sparse signal, or a low-rank matrix, or, more generally, a structured signal, are now well understood.  Indeed, this boils down to a question in random matrix theory:  How well conditioned is a random matrix restricted to a fixed subset of R^n?  We discuss recent work addressing this question in the sub-Gaussian case.  Nevertheless, a practitioner with a fixed data set will wonder:  Can they apply theory based on randomness?  Is there any hope to get the same guarantees?  We discuss these questions in compressive sensing and matrix completion, which, surprisingly, seem to have divergent answers.


Date Heure/Time : Le vendredi 22 novembre 2019 - 16:00

Lieu/Venue : UQAM, Pavillon Président-Kennedy - 201, avenue du Président-Kennedy, salle PK-5115

Conférencier/Speaker : Donald Estep, Simon Fraser University

Titre/Title : Formulation and solution of stochastic inverse problems for science and engineering models

Resume/Abstract :
The stochastic inverse problem of determining probability structures on input parameters for a physics model corresponding to a given probability structure on the output of the model forms the core of scientific inference and engineering design. We describe a formulation and solution method for stochastic inverse problems that is based on functional analysis, differential geometry, and probability/measure theory. This approach yields a computationally tractable problem while avoiding alterations of the model like regularization and ad hoc assumptions about the probability structures. We present several examples, including a high-dimensional application to determination of parameter fields in storm surge models. We also describe work aimed at defining a notion of condition for stochastic inverse problems and tackling the related problem of designing sets of optimal observable quantities.


Date Heure/Time : Le vendredi 29 novembre 2019 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Persi Diaconis, Stanford University

Titre/Title : Shuffling and Group Representations

Resume/Abstract :
Picture n cards, numbered 1,2,...,n face down, in order, in a row on the table. Each time, your left hand picks a random card, your right hand picks a random card and the two cards are transposed. It is clear that 'after a while' the cards get all mixed up. How long does this take? In joint work with Mehrdad Shahshahani we analyzed this problem using the character theory of the symmetric group. The methods work for general measures on general compact groups. They mix probability, analysis, combinatorics and group theory (we need real formulas for the representations). I will try to explain all of this(along with some motivation for studying such problems) 'in English'. The answer, when n=52, is 'about 400'.


Date Heure/Time : Le vendredi 17 janvier 2020 - 16:00

Lieu/Venue : Pavillon André-Aisenstadt, Université de Montréal, salle 6214-6254

Conférencier/Speaker : Éva Tardos, Cornell University

Titre/Title : À venir

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À venir / Coming soon


Date Heure/Time : Le vendredi 24 janvier 2020 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Olivier Lafitte, Unité Mixte Internationale – Centre de recherches mathématiques (UMI-CRM).

Titre/Title : Propagation des ondes et diffraction par un obstacle: résultats utilisant l’analyse microlocale

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À venir / Coming soon


Date Heure/Time : Le vendredi 31 janvier 2020 - 16:00

Lieu/Venue : HEC Montréal, 3000, chemin de la Côte-Sainte-Catherine, salle Béton Grilli

Conférencier/Speaker : Ana-Maria Staicu, North Carolina State University

Titre/Title : Longitudinal functional regression: tests of significance 

Resume/Abstract :
We consider longitudinal functional regression, where, for each subject, the response consists of multiple curves observed at different time visits. We discuss tests of significance in two general settings. First, when there are no additional covariates, we develop a hypothesis testing methodology for formally assessing that the mean function does not vary over time. Second, in the presence of other covariates, we propose a testing procedure to determine the significance of the covariate's time-varying effect formally. The methods account for the complex dependence structure of the response and are computationally efficient. Numerical studies confirm that the testing approaches have the correct size and are have a superior power relative to available competitors. We illustrate the methods on a real data application.


Date Heure/Time : Le vendredi 7 février 2020 - 16:00

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Date Heure/Time : Le vendredi 14 février 2020 - 16:00

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Date Heure/Time : Le vendredi 21 février 2020 - 16:00

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Date Heure/Time : Le vendredi 28 février 2020 - 16:00

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Date Heure/Time : Le vendredi 6 mars 2020 - 16:00

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Date Heure/Time : Le vendredi 13 mars 2020 - 16:00

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Date Heure/Time : Le vendredi 20 mars 2020 - 16:00

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Date Heure/Time : Le vendredi 27 mars 2020 - 16:00

Lieu/Venue : McGill University, Burnside Hall , 805 O., rue Sherbrooke, salle 1104

Conférencier/Speaker : Samit Dasgupta, Duke University

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Date Heure/Time : Le vendredi 3 avril 2020 - 16:00

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Date Heure/Time : Le vendredi 17 avril 2020 - 16:00

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Conférencier/Speaker : Lai Sang Young, NYU

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Date Heure/Time : Le vendredi 24 avril 2020 - 16:00

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Date Heure/Time : Le vendredi 1 mai 2020 - 16:00

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Conférencier/Speaker : Yevgeny Liokumovich , University of Toronto

Titre/Title : Conférence Nirenberg du CRM , À venir

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Date Heure/Time : Le vendredi 8 mai 2020 - 16:00

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Conférencier/Speaker : Antoine Song , Clay Institute

Titre/Title : Conférence Nirenberg du CRM , À venir

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Date Heure/Time : Le vendredi 15 mai 2020 - 16:00

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