1,336 Works

Type theories and polynomial monads

Steve Awodey
A system of dependent type theory T gives rise to a natural transformation p : Terms $\to$ Types of presheaves on the category Ctx of contexts, termed a "natural model of T". This map p in turn determines a polynomial endofunctor P : $\widehat{Ctx}$ $\to$ $\widehat{Ctx}$ on the category of all presheaves. It can be seen that P has the structure of a monad just if T has $\Sigma$-types and a terminal type, and that...

Mathematical and numerical aspects of frame theory - Part 2

Hans G. Feichtinger
Motivated by the spectrogram (or short-time Fourier transform) basic principles of linear algebra are explained, preparing for the more general case of Gabor frames in time-frequency analysis. The importance of the singular value decomposition and the four spaces associated with a matrix is pointed out, and based on this the pseudo-inverse (leading later to the dual Gabor frame) and the Loewdin (symmetric) orthogonalization are explained.

Tame relatively supercuspidal representations

Fiona Murnaghan
Let G be a connected reductive p-adic group that splits over a tamely ramified extension. Let H be the fixed points of an involution of G. An irreducible smooth H-distinguished representation of G is H-relatively supercuspidal if its relative matrix coefficients are compactly supported modulo H Z(G). (Here, Z(G) is the centre of G.) We will describe some relatively supercuspidal representations whose cuspidal supports belong to the supercuspidals constructed by J.K. Yu.

Additive combinatorics methods in fractal geometry - lecture 1

Peter Varju
In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for explicit values of the parameter.

Asymptotic behavior of the Laplacian quasi-maximum likelihood estimator of affine causal processes

Jean-Marc Bardet
We prove the consistency and asymptotic normality of the Laplacian Quasi-Maximum Likelihood Estimator (QMLE) for a general class of causal time series including ARMA, AR($\infty$), GARCH, ARCH($\infty$), ARMA-GARCH, APARCH, ARMA-APARCH,..., processes. We notably exhibit the advantages (moment order and robustness) of this estimator compared to the classical Gaussian QMLE. Numerical simulations confirms the accuracy of this estimator.

Geometric description of the spherical Spin-Glass Gibbs measures and temperature chaos

Gérard Ben Arous
The Gibbs measure of many disordered systems at low temperature may exhibit a very strong dependance on even tiny variations of temperature, usually called “temperature chaos”. I will discuss this question for Spin Glasses. I will report on a recent work with Eliran Subag (Courant) and Ofer Zeitouni (Weizmann and Courant), where we give a detailed geometric description of the Gibbs measure at low temperature, which in particular implies temperature chaos for a general class...

The evolution of cooperation in an iterated survival game

John Wakeley
A new type of a simple iterated game with natural biological motivation is introduced. Two individuals are chosen at random from a population. They must survive a certain number of steps. They start together, but if one of them dies the other one tries to survive on its own. The only payoff is to survive the game. We only allow two strategies: cooperators help the other individual, while defectors do not. There is no strategic...

Table ronde : mathématiques vivantes dans le monde

Pierre Arnoux, Valérie Henry, Samia Mehaddene, Ali Rahmouni & Saliou Touré
Présentation des systèmes scolaires et des mathématiques enseignés dans différents pays francophones (Belgique, Tunisie, Algérie, Côte d'Ivoire) avec quatre professeurs qui partagent leurs expériences.

Cluster algebras and categorification - Lecture 2

Claire Amiot
In this course I will first introduce cluster algebras associated with a triangulated surface. I will then focus on representation of quivers, and show the strong link between cluster combinatorics and representation theory. The aim will be to explain additive categorification of cluster algebras in this context. All the notions will be illustrated by examples.

Calcul tensoriel formel sur les variétés différentielles - Partie 1

Éric Gourgoulhon
Le calcul tensoriel sur les variétés différentielles comprend l'arithmétique des champs tensoriels, le produit tensoriel, les contractions, la symétrisation et l'antisymétrisation, la dérivée de Lie le long d'un champ vectoriel, le transport par une application différentiable (pullback et pushforward), mais aussi les opérations intrinsèques aux formes différentielles (produit intérieur, produit extérieur et dérivée extérieure). On ajoutera également toutes les opérations sur les variétés pseudo-riemanniennes (variétés dotées d'un tenseur métrique) : connexion de Levi-Civita, courbure, géodésiques,...

On the work and persona of Gilles Lachaud

Sudhir Ghorpade
I will give an account of some aspects of the mathematical work of Gilles Lachaud, especially the work in which I was associated with him. This will be mixed with some personal reminiscences.

Isolated points on modular curves

Bianca Viray
Faltings’s theorem on rational points on subvarieties of abelian varieties can be used to show that al but finitely many algebraic points on a curve arise in families parametrized by $\mathbb{P}^{1}$ or positive rank abelian varieties, we call these finitely many exceptions isolated points. We study how isolated points behave under morphisms and then specialize to the case of modular curves. We show that isolated points on $X_{1}(n)$ push down to isolated points on aj...

The symplectic type of congruences between elliptic curves

John Cremona
In this talk I will describe a systematic investigation into congruences between the mod $p$ torsion modules of elliptic curves defined over $\mathbb{Q}$. For each such curve $E$ and prime $p$ the $p$-torsion $E[p]$ of $E$, is a 2-dimensional vector space over $\mathbb{F}_{p}$ which carries a Galois action of the absolute Galois group $G_{\mathbb{Q}}$. The structure of this $G_{\mathbb{Q}}$-module is very well understood, thanks to the work of J.-P. Serre and others. When we say...

Ore polynomials and application to coding theory

Xavier Caruso
In the 1930’s, in the course of developing non-commutative algebra, Ore introduced a twisted version of polynomials in which the scalars do not commute with the variable. About fifty years later, Delsarte, Roth and Gabidulin realized (independently) that Ore polynomials could be used to define codes—nowadays called Gabidulin codes—exhibiting good properties with respect to the rank distance. More recently, Gabidulin codes have received much attention because of many promising applications to network coding, distributed storage...

Good recursive towers

Alp Bassa
Curves over finite fields of large genus with many rational points have been of interest for both theoretical reasons and for applications. In the past, various methods have been employed for the construction of such curves. One such method is by means of explicit recursive equations and will be the emphasis of this talk.The first explicit examples were found by Garcia–Stichtenoth over quadratic finite fields in 1995. Afterwards followed the discovery of good towers over...

The coset leader weight enumerator of the code of the twisted cubic

Ruud Pellikaan
In general the computation of the weight enumerator of a code is hard and even harder so for the coset leader weight enumerator. Generalized Reed Solomon codes are MDS, so their weight enumerators are known and its formulas depend only on the length and the dimension of the code. The coset leader weight enumerator of an MDS code depends on the geometry of the associated projective system of points. We consider the coset leader weight...

Classes of Heegner divisors and traces of singular moduli

Jan Bruinier
In parallel to the Gross-Kohnen-Zagier theorem, Zagier proved that the traces of the values of the j-function at CM points are the coefficients of a weakly holomorphic modular form of weight 3/2. Later this result was generalized in different directions and also put in the context of the theta correspondence. We recall these results and report on some newer aspects.

A tale of Pfaffian persistence tails told by a Bonnet-Painlevé VI transcendent

Ivan Dornic
We identify the persistence probability for the zero-temperature non-equilibrium Glauber dynamics of the half-space Ising chain as a particular Painlevé VI transcendent, with monodromy exponents (1/2,1/2,0,0). Among other things, this characterization a la Tracy-Widom permits to relate our specific Bonnet-Painlevé VI to the one found by Jimbo & Miwa and characterizing the diagonal correlation functions for the planar static Ising model. In particular, in terms of the standard critical exponents eta=1/4 and beta=1/8 for the...

Fluid-structure interaction in the cardiovascular system. Lecture 2: Cardiac valves

Jean-Frédéric Gerbeau
I will introduce the topic of computational cardiac electrophysiology and electrocardiograms simulation. Then I will address some questions of general interest, like the modeling of variability and the extraction of features from biomedical signals, relevant for identification and classification. I will illustrate this research with an example of application to the pharmaceutical industry.

On centauric subshifts

Andrei Romashchenko
We discuss subshifts of finite type (tilings) that combine virtually opposite properties, being at once very simple and very complex. On the one hand, the combinatorial structure of these subshifts is rather simple: we require that all their configurations are quasiperiodic, or even that all configurations contain exactly the same finite patterns (in the last case a subshift is transitive, i.e., irreducible as a dynamical system). On the other hand, these subshifts are complex in...

Toeplitz determinants, Painlevé equations, and special functions. Part II: a Riemann-Hilbert point of view - Lecture 1

Alexander R. Its
Starting with Onsager's celebrated solution of the two-dimensional Ising model in the 1940's, Toeplitz determinants have been one of the principal analytic tools in modern mathematical physics; specifically, in the theory of exactly solvable statistical mechanics and quantum field models. Simultaneously, the theory of Toeplitz determinants is a very beautiful area of analysis representing an unusual combinations of profound general operator concepts with the highly nontrivial concrete formulae. The area has been thriving since the...

Forward and backward simulation of Euler scheme

Emmanuel Gobet
We analyse how reverting Random Number Generator can be efficiently used to save memory in solving dynamic programming equation. For SDEs, it takes the form of forward and backward Euler scheme. Surprisingly the error induced by time reversion is of order 1.

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