Matthieu Kowalski

Evènements passés et à venir


Mercredi 15 mai: séminaire MAORI à Toulouse

Lieu: Toulouse

Programme:
09:30 - 10:00 : accueil des participants
10:00 - 11:00 : présentation de Claire Boyer: Sampling by blocks of measurements in Compressed Sensing
11:00 - 12:00 : présentation de Nicolas Chauffert: From independent to continuous sampling in MRI: two alternative approaches
12:00 - 14:00 : déjeuner
14:00 - 15:00 : présentation de Emilie Chouzenoux: Variable Metric Forward-Backward Algorithm
15:00 - fin : discussions et groupes de travail

Lundi 15 avril : Séminaires de Pierre Machart et Giovanni Cherchia

Lieu: Télécom ParisTech

Programme :

09:30 - 10:30 : accueil des participants
10:30 - 12:00 :
présentation de Pierre Machart: Non-Asymptotic Analysis for a Computationally Optimal Trade-O f for Inexact Proximal Methods

Résumé:
In this work, we investigate the trade-off  between convergence rate and computational cost when minimizing a composite functional with proximal-gradient methods, which are popular optimisation tools in machine learning and signal processing. We consider the case when the proximity operator is computed via an iterative procedure, which provides an approximation of the exact proximity operator. In that case, we obtain algorithms with two nested loops. We show that the strategy that minimizes the computational cost to reach a solution with a desired accuracy in finite time is to set the number of inner iterations to a constant, which diff ers from the strategy indicated by a convergence rate analysis. In the process, we also present a new procedure called SIP (that is Speedy Inexact Proximal-gradient algorithm) that is both computationally e fficient and easy to implement. Our numerical experiments confi rm the theoretical findings and suggest that SIP can be a very competitive alternative to the standard procedure.


12:00 - 14:00 : déjeuner
14:00 - 15:00 : présentation de  Giovanni Cherchia: "An epigraphical convex optimization approach for multicomponent image restoration using non-local structure tensor "
15:00 - 17:00 : Discussions



Kick off meeting : Mercredi 19 décembre (Lieu : IHP)

Programme :

09:30 - 10:00 : accueil des participants
10:00 - 10:30 : tour de table rapide + pause café
10:30 - 12:00 : thème algo accéléré
Tutorial : Matthieu -- méthode d’active sets
Discussions
12:30 - 14:00 : déjeuner (buffet sur place)
14:00 - 15:30 : thème méthodes d'éclatement
Tutorial : Jalal -- méthode métrique variable
Discussions
15:30 - 16:00 : thème sensibilité et estimateurs du risque
Tutorial : Gabriel -- calcul du SURE
Discussion
16:00 - 16:30 : pause café
16:30 - 17:30 : thème application 
Tutorial : Alexandre et Philippe -- l'imagerie fMRI et la parcimonie
Discussion
Slides d'Alexandre
Slides 1 et Slides 2 de Philippe
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