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Prochains exposés

SPOT 57 – Lundi 7 Janvier 2019 –  Amphi des thèses ENSEEIHT
 
14h – Hristo Sendov (University of Western Ontario)

Polar convexity and critical points of polynomials

A set A, in the extended complex plane, is called convex with respect to a pole $u$, if for any $x,y \in A$ the arc on the unique circle through $x,y$, and $u$, that connects $x$ and $y$ but does not contain $u$, is in $A$. If the pole $u$ is taken at infinity, then this notion reduces to the usual convexity. Polar convexity is connected with the classical Gauss-Lucas’ and Laguerre’s theorems for complex polynomials. If a set is convex with respect to $u$ and contains the zeros of a polynomial, then it contains the zeros of its polar derivative with respect to $u$. A set may be convex with respect to more than one pole. The main goal of this talk is to present the main relationships between sets and their poles. This is a joint work with Blagovest Sendov from the Bulgarian Academy of Sciences.

15h – Charles Dossal (INSA and IMT Toulouse)
Exact decay rate for Nesterov Acceleration
 In this presentation, we will give new and optimal decay rates for the Nesterov Acceleration scheme of classical gradient descent depending on the local geometry of the function to minimize. Only bounds on the rates are known for convex or strongly convex functions and we will give a more precise and complete description of this rates using Lojasievicz and flatness conditions.
We will explain how these decays can be obtained studying an ODE.
This work is a Joint work with V. Apidopoulos, JF. Aujol and A. Rondepierre.

Comité local d’organisation

Cf un glossaire expliquant ces sigles et affiliations du système universitaire toulousain.


 Fréquence et structure

Une séance par mois environ, avec deux conférenciers chaque fois (deux conférences de type différent : une orientée fondements et une orientée applications, un conférencier de l’environnement toulousain et un conférencier extérieur, un conférencier du milieu académique et un conférencier du milieu de l’industrie et des services, etc.).

Horaire habituel : le lundi après-midi de 14h à 16h.


Lieu

Sauf indication contraire, à l’amphithéâtre des (SPOT-) thèses à l’ENSEEIHT (N7), 2 rue Charles Camichel, 31000 Toulouse  (métro B, François Verdier). Attention, présentez-vous au poste de garde afin d’accéder au site.