Geometric Numerical Methods: From Random Fields to Shape Matching
Doctoral thesis, 2025

Geometry is central to many applied problems, though its influence varies. Some problems are inherently geometric, requiring numerical methods that preserve the underlying structure to remain accurate. Others are well understood in Euclidean space but demand different techniques when extended to curved settings. This thesis addresses such geometric challenges through studying numerical methods for two main types of problems: matching problems and stochastic (partial) differential equations. It is based on seven papers: the first three focus on SPDEs and SDEs, while the remaining consider matching problems and related differential equations. The first develops a numerical method for fractional SPDEs on the sphere, combining a recursive splitting scheme with surface finite elements. The second studies a Chebyshev–Galerkin approach for simulating non-stationary Gaussian random fields on hypersurfaces. The third introduces a geometric integrator for stochastic Lie–Poisson systems, derived via a reduction of the implicit midpoint method for canonical Hamiltonian systems. The fourth explores sub-Riemannian shape matching, where shapes are matched using constrained motions, and shows how this problem can be interpreted as a neural network. The fifth studies the convergence of a gradient flow for the Gaussian Monge problem. The sixth adapts geometric shape matching to recover protein conformations from single-particle Cryo-EM data by using rigid deformations of chains of particles. The seventh investigates the numerical signature of blow-up in hydrodynamic equations, showing that numerical solutions can be used to detect the onset in a class of hydrodynamic equations.

hydrodynamics

Stochastic partial differential equations

Lie–Poisson systems

shape analysis

geometric numerical integration

optimal transport

surface finite element methods

Gaussian random fields

Pascal
Opponent: Professor Stefan Sommer, Department of Computer Science, University of Copenhagen, Denmark

Author

Erik Jansson

Chalmers, Mathematical Sciences, Applied Mathematics and Statistics

Surface finite element approximation of spherical Whittle-Matérn Gaussian random fields

SIAM Journal of Scientific Computing,;Vol. 44(2022)p. A825-A842

Journal article

Jansson E., Modin, K. "Sub-Riemannian Landmark Matching and its interpretation as residual neural networks"

CONVERGENCE OF THE VERTICAL GRADIENT FLOW FOR THE GAUSSIAN MONGE PROBLEM

Journal of Computational Dynamics,;Vol. 11(2024)p. 1-9

Journal article

Jansson E., Krook, J., Modin, K., Öktem, O. "Geometric shape matching for recovering protein conformations from single-particle Cryo-EM data"

Jansson E., Modin, K. "On the numerical signature of blow-up in hydrodynamic equations"

Although mathematics is foundational to science, few real-world problems can be solved exactly through pen-and-paper calculations. Instead, numerical methods are employed to find approximate solutions. This thesis is a contribution to the fields of computational mathematics and numerical analysis.  These branches of mathematics develop and analyze the properties of numerical methods, determining when they can be used, how effective they are, and when they fail.
 More specifically, this work addresses geometric problems, such as differential equations on curved spaces or mechanical systems, for which it is essential to ensure that the approximate solutions are physically plausible. The applications discussed range from generating random fields on surfaces to reconstructing protein conformations from noisy microscopy data, all of which are inherently geometric problems.

Subject Categories (SSIF 2025)

Probability Theory and Statistics

Computational Mathematics

Geometry

ISBN

978-91-8103-208-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5666

Publisher

Chalmers

Pascal

Opponent: Professor Stefan Sommer, Department of Computer Science, University of Copenhagen, Denmark

More information

Latest update

4/28/2025