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CIRM – Centre International de Rencontres Mathématiques

Solving time-harmonic wave equations with iterative methods is very challenging because they combine multiple difficulties like e.g. highly oscillatory solutions and complex non-Hermitian and indefinite discrete operators. In addition, the wave number associated to the numerical solution is different from the one of the exact solution thus leading to so-called numerical dispersion which requires very fine mesh to be controlled. There exists numerical schemes designed to reduce the dispersion error where the most used technique to build them relies on stencils involving free parameters that are next obtained by numerically minimizing the dispersion error. In the past few years, we develop an alternative approach called asymptotic dispersion correction. The latter is based on the introduction of a perturbation of the wavenumber (the shift) in the numerical scheme. We then explicitly compute the shift that minimizes the dispersion error for small enough meshsize. In addition, we show that our method can be applied to any finite difference scheme and reduces the relative error. We emphasize that most of works dealing with dispersion reducing methods consider the Helmholtz equation. The goal of the Research in Residence is to extend the asymptotic dispersion correction to the convected Helmholtz equation that can be used to model time-harmonic wave propagation in a moving flow.

Cours et évènements pour étudiants en mathématiques,    Analyse

CIRM – Centre International de Rencontres Mathématiques

The conference, in advance of a thematic program planned for IHP in 2026, addresses the key role played by completely integrable systems as models for wave phenomena in myriad physical settings such as surface water waves and internal waves, quantum excitations in Bose-Einstein condensates, plasma oscillations, optical fiber telecommunication systems, and solid-state physics. The principal objectives of the CIRM conference are to focus specifically on soliton gases, explicit formulas, and asymptotic behavior in integrable models, and to highlight corresponding novel results and new progress on several previously impenetrable fronts.

Physique mathématique,    Mathématiques appliquées (en général)

CIRM – Centre International de Rencontres Mathématiques

The abstract foundation of the book concerning functional analysis, special issues on Sobolev type function scales, and elliptic and parabolic regularity in case of non-smooth data, is already solid. However, the culminating last part of the book is still under discussion and editing. There, it is intended, using the theory established before, to give a condensed and unified treatment of wellposedness for several real-world problems, namely the thermistor problem, the Keller-Segel chemotaxis model, and the macroscopic semiconductor equations (Van Roosbroeck system) in case of Avalanche generation, all for the case of non-smooth spatial domains. These problems were open for decades and solved only recently by the authors and collaborators in journal articles.

Analyse,    Mathématiques appliquées (en général)