Seminar Physique Mathématique -- Poincaré polynomials for Abelian Symplectic Quotients of Multi-particle Quantum States

11/24/2015 - 15:30
11/24/2015 - 16:30
Saeid Molladavoudi (University of Ottawa)
CRM, UdeM, Pavillon André-Aisenstadt, 2920, ch. de la Tour, salle 4336

We present a mathematical framework to study geometry and topology of quotients for multi-particle quantum systems. In particular, we are interested in geometrical and topological properties of abelian symplectic reduced spaces of pure multipartite states, as complex projective spaces, which are acted upon in a Hamiltonian fashion by maximal tori of the semisimple compact Local Unitary Lie groups. We discuss that the existing geometrical methods equip us with a powerful set of tools to compute topological invariants for these reduced spaces. More precisely, given the components in the moment (Kirwan) polytope for multi-qubits, we utilize a recursive wall-crossing formula for the Poincaré polynomials and Euler characteristics of abelian symplectic quotients and as some examples we elaborate the procedure for quantum systems with two and three qubits in their pure states and propose an algorithm for a general r-qubits.

Last edited by on Mon, 11/23/2015 - 17:14

Seminar Séminaire de la topologie computationnelle du SAG

11/24/2015 - 14:00
11/24/2015 - 15:00
Chaima Hamdi (Université de Sherbrooke)
Université de Sherbrooke, salle D4-2020
Last edited by on Mon, 11/23/2015 - 17:13

Geometrically-induced spin precession in kerr geometry

12/02/2015 - 13:45
12/02/2015 - 15:30

 The Department of Mathematics and Statistics invites you to attend the Ph.D. Oral Defense of Mr. Anusar Farooqui.


Last edited by on Wed, 11/18/2015 - 15:10

Overcoming Order-loss in High-order Time-stepping

11/23/2015 - 15:00
11/23/2015 - 16:00
Dong Zhou (Temple University)
Burnside Hall, Rm. 920 (McGill University)

This talk focuses on a fundamental problem that arises with high-order time-stepping in initial boundary values problems: a loss of convergence order incurred with multistage Runge-Kutta methods. We will demonstrate the underlying mechanisms that lead to order loss via both examples and numerical analysis, and provide conditions that time-stepping schemes need to satisfy so that order-loss arises or does not arise. We then present a remedy that is based on modifying the boundary conditions. Numerical tests show that this approach recovers full convergence order of the time-stepping schemes. Moreover, the proposed fixes apply to both linear and nonlinear problems.

Last edited by on Wed, 11/18/2015 - 10:35

Sur l'étude des singularités dans des modèles mathématiques de cristaux liquides

11/20/2015 - 16:00
11/20/2015 - 17:00
Lia Bronsard (McMaster University)
UQAM, Pavillon Sherbrooke, Salle SH-2420

L'analyse de modèles mathématiques pour les cristaux liquides pose beaucoup de défis, vu leurs proximités à l'étude des singularités dans les applications harmoniques. Dans ce colloque, je vais présenter des modèles mathématiques utilisés dans l'étude des cristaux liquides, la connexion avec les résultats classiques pour les applications harmoniques, ainsi que les nouvelles méthodes utilisées pour étudier les singularités dans le modèle de Landau-de Gennes. Ce modèle permet une plus grande variété de singularités que le modèle d'Oseen-Frank basé sur les applications harmoniques à valeur dans la sphère.

Last edited by on Thu, 11/12/2015 - 17:14

Seminar Geometry-Topology -- Hypercomplex manifolds of dimension 8

11/20/2015 - 11:00
11/20/2015 - 12:00
Mehdi Lejmi (UQAM)
UQAM, Pavillon Président-Kennedy, PK-5115

The goal of the talk is to prove a quaternionic analog of the well-known fact that a compact complex surface is kähler if and only if its first Betti number is even. More precisely, we prove that a compact 8-dimensional SL(2,H) manifold admits an hyperkähler with torsion metric if and only if its Hodge number h^{0,1} is even. This is a joint work with Gueo Grantcharov and Misha Verbitsky.

Last edited by on Thu, 11/12/2015 - 17:10

Grande conférence du CRM -- Documentary: «Counting from Infinity, Yitang Zhang and the Twin Prime Conjecture»

11/19/2015 - 19:30
11/19/2015 - 21:00
Profs. Granville (UdeM) and Soundararajan (Stanford University)
Université de Montréal, Pavillon Jean-Coutu, 2940, chemin de Polytechnique, Salle S1-151
Last edited by on Thu, 11/12/2015 - 17:08

Working Seminar Mathematical Physics -- Cluster algebras and Grassmannians II

11/19/2015 - 16:00
11/19/2015 - 17:30
Marco Bertola (Concordia, CRM)
Concordia University, Math Help Center, Rm. 912.00/Library Building, 1400 de Maisonneuve Blvd. West, Montréal

After reviewing the notion of Grassmannians and Plucker coordinates, I will review the notion of positivity and then  discuss how Cluster algebras are used in  the coordinatization of Gr_{k,n} (Based on L. Williams talk/paper + Postnikov)

Refs:  1) L. K. Williams, Cluster algebrasm an introduction, Bull  Amer. Math. Soc. (New Series) vol. 51,  No. 1, 1–26 (2014) 2) K. Rietsch and L. Williams, "Cluster duality and mirror symmetry  for Grassmannianss, arXiv1507.07817 3) Alexander Postnikov, "Total positivity, Grassmannians, and networks."

Last edited by on Thu, 11/12/2015 - 17:04

Colloquium DIRO -- Meaning banking and beyond

11/18/2015 - 11:30
11/18/2015 - 12:30
Valerio Basile (Inria, Sophia Antipolis)
Université de Montréal, Pavillon André-Aisenstadt, 2920 ch. de la Tour, Salle 3195

The progress of Natural Language Processing through the eighties and the nineties allowed us to build large collections of text in electronic format annotated with all kind of linguistic information. These corpora are often called "treebanks", alluding to the tree-like structure of the syntactic analysis of natural language. More recently, researchers have started to employ more sophisticated tools to analyze the meaning of natural language, thus creating "meaning banks". In this talk I will present the Groningen Meaning Bank, a free resource of semantically annotated English text, with particular emphasis on the software toolchain that performs the analysis of the meaning.

In the second part of the talk, I will present the work in progress on integrating the GMB software pipeline with the Linked Open Data ecosystem via entity linking. The integration aims to create an end-to-end system inspired by the Learning by Reading paradigm. The system extracts DBpedia entities and relations from raw text, and it is being used in the context of the ALOOF project in order to enable domestic robots learn new information about their environment by "reading" the Web.

Last edited by on Thu, 11/12/2015 - 17:01

Seminar Statistique Sherbrooke -- Les polynômes de Bernstein: indomptables lisseurs

11/17/2015 - 15:30
11/17/2015 - 16:30
Félix Camirand-Lemyre (Université de Sherbrooke)
Université de Sherbrooke 2500, boul. de l'Université, Salle D4-2019. Sherbrooke (Québec)

Lorsque l’on souhaite vérifier si un jeu de données peut être décrit par une fonction de répartition (ou densité) appartenant à une certaine famille paramétrique, il est souvent convenable de comparer un estimateur non paramétrique de la fonction avec le modèle considéré. Il s’avère qu’en pratique, les estimateurs non paramétriques de la densité basés sur les polynômes de Bernstein sont d’une efficacité déconcertante lorsque les variables considérées sont à support compact. Or, obtenir leur loi limite n’est pas une mince affaire !

Durant cette présentation, il sera d’abord question de l’estimation de densité par les polynômes de Bernstein, puis on construira un test d’adéquation basé sur l’estimateur résultant, et on obtiendra sa loi limite…avec l’aide de quelques astuces de calcul !

Last edited by on Thu, 11/12/2015 - 16:59