Séminaire ISTerre

Differentiable spectral methods for geophysical fluid dynamics

vendredi 10 octobre 2025 - 09h30
Keaton Burns - MIT Math
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Global spectral methods are a classical technique for solving partial differential equations (PDEs), including Fourier series in periodic domains and orthogonal polynomials in bounded domains. While traditional collocation-based approaches for polynomials are slow at scale, modern spectral methods reformulate these systems in sparse operator form, enabling fast and accurate solvers with near FFT-like performance in geometries such as channels, disks, and spheres. These sparse methods are also amenable to automatic differentiation (autodiff), enabling efficient PDE-based optimization as well as forward modeling.

Here we will present Dedalus, an open-source Python framework for solving general PDEs using modern sparse spectral methods. Unlike traditional domain-specific solvers, Dedalus does not hard-code particular equation sets, but instead provides a symbolic equation specification system that allows users to define their own PDEs. The framework then automatically constructs an optimally sparse, MPI-parallelized solver tailored to the chosen equations and geometry. This flexibility has enabled Dedalus to support a wide range of interdisciplinary applications, including many for which specialized solvers do not yet exist.

We will also introduce a new autodiff system that can compute the discrete adjoint of any Dedalus solver. Adjoint methods are central to optimization in CFD, including parameter estimation and nonlinear stability analyses, but are traditionally cumbersome to derive and implement. Reverse-mode autodiff, by contrast, automates these computations at the compiler level and has become a mainstay of differential programming in machine learning. Our approach efficiently implements reverse-mode differentiation by leveraging Dedalus's symbolic equation representation, requiring no differentiable compiler and preserving full MPI parallelism. We will demonstrate the capabilities of this system with applications including optimal perturbations in shear flows and kinematic dynamos.

Equipe organisatrice : Géodynamo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

Informations de visio :

https://univ-grenoble-alpes-fr.zoom.us/j/91690538748?pwd=buNDS0rAZw9rG4vS1rWxX53zHYdQaw.1

“Minimalist seismology”: studying earthquakes with sparse instrumentation

jeudi 17 septembre 2026 - 11h00

Mathieu Causse - ISTerre

Equipe organisatrice : Organisation labo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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Stable‑to‑dynamic expansion of fault slipping area through fluid injection observed in laboratory experiments using a sub‑meter scale specimen

vendredi 18 septembre 2026 - 14h00

Takatoshi Ito  - Université de Tohoku, Japan

Equipe organisatrice : Mécanique des failles

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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Tectonics, Mantle Dynamics and Coupled Lithosphere-Mantle-Core Evolution of Earth and Other Rocky Worlds

jeudi 24 septembre 2026 - 11h00

Paul Tackley - ETH Zurich

Equipe organisatrice : Grands Séminaires ISTerre

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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Tectonics, Mantle Dynamics and Coupled Lithosphere-Mantle-Core Evolution of Earth and Other Rocky Worlds

jeudi 24 septembre 2026 - 11h00

Paul Tackley - ETH Zurich

Equipe organisatrice : Grands Séminaires ISTerre

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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Apport des expériences analogiques pour la modélisation et le suivi en temps réel de la propagation du magma en profondeur : Exemple du Rift Est Africain

jeudi 1er octobre 2026 - 11h00

Virginie Pinel - ISTerre

Equipe organisatrice : Organisation labo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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A t-on encore besoin de plaques pour expliquer la tectonique de la vallée du Rhône et des Alpes Occidentales ?

vendredi 2 octobre 2026 - 11h00

philippe VERNANT - Geosciences Montpellier

Equipe organisatrice : Tectonique active et sismicité

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

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TBA

vendredi 2 octobre 2026 - 14h00

Hugo Boulze - 

Equipe organisatrice : Cycle sismique et déformations transitoires

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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TBA

vendredi 9 octobre 2026 - 11h00

Eric Beaucé - ISTerre

Equipe organisatrice : Cycle sismique et déformations transitoires

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

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TBA

vendredi 20 novembre 2026 - 11h00

Farzaneh Mohammadi - ENS Paris

Equipe organisatrice : Cycle sismique et déformations transitoires

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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