Hey! I'm Simon Halvdansson,

a research scientist at SINTEF Energy Research in Trondheim, Norway. I recently finished my PhD, supervised by Professor Franz Luef at NTNU. My mathematical research is in time-frequency analysis using tools from harmonic analysis, functional analysis and operator theory. More specifically, much of the research is connected to the framework of quantum harmonic analysis.

Apart from my interest in mathematics, I have a background in physics, programming and deep learning, and currently maintain the open source Android Hacker News client Harmonic. I have a blog where I write about whatever I find interesting at the moment, mostly connected to the above mentioned topics.

ArXiV CV GitHub LinkedIn

Papers

\(\boldsymbol{ \mathcal{F}_{\mathrm{KO}}(\mathcal{F}_{\mathrm{W}}(S)) }\)
Weyl Quantization of Exponential Lie Groups for Square Integrable Representations
February 2025
with Stine Marie Berge
ArXiV
\(\boldsymbol{ \lambda_k^\Omega \approx \operatorname{erfc}\Big( \sqrt{2\pi} \frac{k - |\Omega|}{|\partial \Omega|} \Big) }\)
Empirical plunge profiles of time-frequency localization operators
February 2025
ArXiV GitHub
\(\boldsymbol{B_\mu^\varphi}\)
On a time-frequency blurring operator with applications in data augmentation
May 2025
Journal of Fourier Analysis and Applications ArXiV GitHub
\(\boldsymbol{\rho_\Omega - \chi_\Omega}\)
On accumulated spectrograms for Gabor frames
November 2024
Journal of Mathematical Analysis and Applications ArXiV
\(\boldsymbol{\mu \star S}\)
Measure-operator convolutions and applications to mixed-state Gabor multipliers
July 2024
with Hans Feichtinger and Franz Luef
Sampling Theory, Signal Processing, and Data Analysis ArXiV
\(\boldsymbol{A_f^g \mapsto f}\)
Five ways to recover the symbol of a non-binary localization operator
February 2025
Journal of Pseudo-Differential Operators and Applications ArXiV GitHub
\(\boldsymbol{f \star_G S}\)
Quantum harmonic analysis on locally compact groups
October 2022
Journal of Functional Analysis ArXiV
\(\boldsymbol{\operatorname{argmin}_f \mathcal{L}_{\mathrm{P}}(f)}\)
Existence of Uncertainty Minimizers for the Continuous Wavelet Transform
August 2021
with Jan-Fredrik Olsen, Ron Levie and Nir Sochen
Mathematische Nachrichten ArXiV

Posts

Talks/posters

PhD Defense
June 11, 2025 · Trondheim, Norway
Slides
PhD Trial Lecture
June 11, 2025 · Trondheim, Norway
Slides
Workshop on Quantum Harmonic Analysis (QHA2024)
August 5-9, 2024 · Hannover, Germany
Slides
More on Harmonic Analysis (Strobl24)
June 9-15, 2024 · Strobl, Austria
Poster
International Workshop on Operator Theory and its Applications (IWOTA 2023)
July 31 - August 4, 2023 · Helsinki, Finland
Slides
Workshop on Quantum Harmonic Analysis (QHA2023)
June 5-9, 2023 · NTNU Trondheim, Norway
Slides
Dynamics in the noncommutative world (DNCW 2023)
January 26, 2023 · NTNU Trondheim, Norway
Slides
Oberseminar Analysis
October 4, 2022 · Leibniz Universität Hannover, Germany
Slides
International Conference on Computational Harmonic Analysis (ICCHA 2022)
September 12-16, 2022 · Ingolstadt, Germany
Slides
International Workshop on Operator Theory and its Applications (IWOTA 2022)
September 6-10, 2022 · Krakow, Poland
Slides
Applied Harmonic Analysis and Friends (Strobl22)
June 19-25, 2022 · Strobl, Austria
Poster
Online International Conference on Computational Harmonic Analysis (ICCHA 2021)
September 13-17, 2021 · Online
Slides

Projects

Harmonic for Hacker News
Harmonic is currently the most popular Hacker News client for Android with over 6000 daily active users and 80 000 downloads. As of summer 2023, it is open source and development is still ongoing. The focus of the app is on customizability, performance and a sleek modern design.
Play Store GitHub
Existence and Approximations of Optimal Wavelets
This is my master's thesis from Lund University, supervised by Jan-Fredrik Olsen and later on also Ron Levie. While relying heavily on earlier work by Ron Levie and Nir Sochen, we investigate an uncertainty functional measuring the localization of a wavelet. As it is a master thesis, there is a large focus on going over previous research and motivating the functional properly. In the end, we show that minimizers exists and can be approximated by considering minimizers on lower dimensional subspaces which can be constructed numerically.
PDF Minimizers
Computations with the 2D Coulomb Gas
My bachelor's thesis, also written at Lund University but with Yacin Ameur, is a thorough introduction to the 2D Coulomb gas and contains some (minor) novel results. The field has quite a deep background which is investigated and we motivate the construction of the main objects of the field. Moreover, there is also a simulation of these types of particle systems which can run with up to 50 000 particles on regular consumer hardware. Originally, the simulator could only handle 5000 particles but I rewrote it to utilize web worker multithreading in 2023. In 2025 I vibe coded a GPU version which can handle 500 000 particles - how the times have changed
PDF Simulator (GPU) Simulator (CPU) GitHub
Pay Back - IOU Manager
In high school I developed a series of Android apps and Pay Back, while quite outdated, is the only one which is still live on the Play Store. It was a joint project with John Rapp Farnes who focused more on the internals while I was responsible for design and UI, however our work often intersected. An IOU (I Owe yoU) manager keeps track of personal debts; this was from before you could painlessly send money to your friends. It has a ton of intricate features such as using NFC to sync your debts with friends which I guess is the highest form of feature creep.
Play Store