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Prochains exposés

SPOT 96 – Lundi 3 Mars – 14h-16h

14h – Valentin Debarnot (University of Basel) – Differentiable Uncalibrated Imaging

We will present our paper ‘Differentiable Uncalibrated Imaging’ where we propose a differentiable imaging framework to address uncertainty in measurement coordinates, such as sensor locations and projection angles. Our approach leverages implicit neural networks and spline-based neural fields to perform joint calibration and image reconstruction. This makes it possible, for example, to use pre-trained neural networks to configurations different from those for which they were originally trained. We will begin by presenting the general optimization framework underlying our method. Next, we will illustrate our approach to 2D and 3D computed tomography, and show that it produces improved reconstructions compared to baselines that do not account for the lack of calibration. Finally, we will explore how this framework extends to the challenging problem of 3D cryo-tomography reconstruction, tackling scenarios with misaligned and noisy input projections.

15h – Tobias Metzlaff  (LAAS-CNRS Toulouse) – Symmetry in Trigonometric Optimization

Symmetry is a ubiquitous phenomenon in nature and science that provides optimal configurations for a variety of problems, such as energy minimization, sampling or sphere packing. In this talk, I will focus on lattice-based symmetries and the problem of minimizing a periodic function on a lattice with an outlook on applications in graph theory. In practice, periodic functions on lattices are approximated by trigonometric polynomials through Fourier expansion. The problem of minimizing a trigonometric polynomial is nonconvex, nonlinear and NP-hard. Over the past decades, this has spiked the interest of the optimization community and has lead to the development of a hierarchy of semi-definite lower bounds, known as the Lasserre-hierarchy. I will show how to exploit symmetry in this hierarchy, address computational and numerical issues that have been overcome in the past years and point towards open questions. Based on joint work with Evelyne Hubert (Sophia Antipolis), Cordian Riener (Tromsø), Philippe Moustrou (Toulouse) and Sebastian Debus (Chemnitz).

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 la salle des thèses (C002) 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.