Prof. Dr. Nicolas Gauger, Chair for Scientific Computing (SciComp), TU Kaiserslautern

SciComp Seminar Series

Please contact Prof. Gauger, if you want to register for an online talk in our SciComp Seminar Series or just to register for the seminar.

A list of the already scheduled talks can be found –> here:

Dr. Marcella Bonazzoli, Inria Saclay Centre at Institut Polytechnique de Paris (Palaiseau, France)

Title: One-shot and domain decomposition methods for inverse problems

Abstract:

When an inverse problem is solved by a gradient-based optimization algorithm, the corresponding forward and adjoint problems, which are introduced to compute the gradient, can be also solved iteratively, for instance by domain decomposition methods. In this framework, one-shot inversion methods iterate at the same time on the inverse problem unknown and on the forward and adjoint problem solutions. We are especially interested in the case where the inner iterations for the direct and adjoint problems are incomplete, that is, stopped before achieving a high accuracy on their solutions.
We analyze the convergence of one-shot methods for general linear inverse problems and fixed-point iterations for the associated forward/adjoint problems. In particular, we establish sufficient conditions on the descent step for convergence, which are explicit in the number of inner iterations. We provide numerical experiments, for linear and non linear inverse problems, to illustrate the convergence of these methods in comparison with the classical gradient descent method, where the forward and adjoint problems are solved exactly by a direct solver instead.
This is joint work with Tuan Anh Vu and Houssem Haddar.

How to join online

You can join online via Zoom, using the following link:
https://uni-kl-de.zoom.us/j/63123116305?pwd=Yko3WU9ZblpGR3lGUkVTV1kzMCtUUT09

Lea Fischer, University of Göttingen

Title: Proximal Block Implicit-Explicit Algorithm for Near-field Ptychography

Abstract:

The talk explores the application of the Proximal Heterogeneous Block Input-Output Method (PHeBIE) algorithm to the blind near-field ptychography problem. The structure of the near-field ptychography problem uses lateral and longitudinal shifts of the object. The talk begins with an introduction to fundamental concepts of numerical analysis, focusing on the Fourier transform and the Fresnel near-field propagator. We present an approach to near-field ptychography using lateral and longitudinal shifts, as well as the PHeBIE algorithm. The core of this work lies in the application of the PHeBIE algorithm to near-field ptychography. The resulting new algorithm is implemented in Python and numerical results are presented.