Fourth annual conference of the SFB-TRR 195

The Fourth annual conference of the SFB-TRR 195 took place virtually on Sept. 22–24, 2020. The goal of the conference was to bring together people from different areas in algebra who apply computational methods in their research. The main organizer is Ulrich Thiel (TU Kaiserslautern), see contact details below. Slides and recordings can be found in the list of talks below.

Impressions

Here are some impressions of the conference.

Conference Portal

Rooms are accessible via the conference portal. Access code was sent to registered participants.

Speakers

From outside the SFB-TRR

Philippe Biane, Université Paris-Est

Tim Dokchitser, University of Bristol

Olivier Dudas, Université Paris Diderot

Gavril Farkas, Humboldt-Universität zu Berlin

Lars Thorge Jensen, University of Clermont Auvergne

Eric Katz, The Ohio State University

Yue Ren, Swansea University

Michael Stillman, Cornell University

Nicolas Thiéry, Université Paris Sud

From within the SFB-TRR

Simon Brandhorst, Universität des Saarlandes

Claus Fieker, TU Kaiserslautern

Anne Frühbis-Krüger, Universität Oldenburg

Johannes Flake, RWTH Aachen

Laura Maaßen, RWTH Aachen

Pascal Schweitzer, TU Kaiserslautern

Andrea Thevis, Universität des Saarlandes

Gabriela Weitze-Schmithüsen, Universität des Saarlandes

Schedule

You can find the schedule here (PDF).

Talks

Philippe Biane, Université Paris-Est

Free Lévy processes

There is a notion of processes with free increments in free probability theory which parallels that of processes with independent increments in classical probability. When one tries to characterize those which are time homogeneous (like Lévy processes in classical
probability theory) one finds that there are two natural classes: those with homogeneous increments and those with homogeneous transition probabilities. I will explain how these classes are parameterized by convex sets of analytic functions on the upper half-plane.

Tim Dokchitser, University of Bristol

I will review available packages for p-adic numbers and their extensions in computer algebra systems, focussing on the recent one in Magma by Christopher Doris. It provides lazy exact arithmetic, and is the first native implementation for provable p-adic computations.

Olivier Dudas, Université Paris Diderot

Computing decomposition numbers for finite unitary groups

(work in progress with R. Rouquier) In this talk I will present a computational (yet conjectural) method to determine some decomposition matrices for finite groups of Lie type. I will first explain how one can produce a “natural” self-equivalence in the case of $\mathrm{GL}_n(q)$ coming from the topology of the Hilbert scheme of $\mathbb{C}^2$. The combinatorial part of this equivalence is related to Macdonald’s theory of symmetric functions and gives $(q,t)$-decomposition numbers. The evidence suggests that the case of finite unitary groups is obtained by taking a suitable square root of that equivalence.

Gavril Farkas, Humboldt-Universität zu Berlin

Green’s Conjecture via Koszul modules

Using ideas from geometric group theory we provide a novel approach to Green’s Conjecture on syzygies of canonical curves. Via a strong vanishing result for Koszul modules we deduce that a general canonical curve of genus g satisfies Green’s Conjecture when the characteristic is zero or at least (g+2)/2. Our results are new in positive characteristic (and answer positively a conjecture of Eisenbud and Schreyer), whereas in characteristic zero they provide a different proof for theorems first obtained in two landmark papers by Voisin. Joint work with Aprodu, Papadima, Raicu and Weyman.

Lars Thorge Jensen, University of Clermont Auvergne

How to teach a computer the Elias-Williamson graphical calculus? [Slides]

Based on recent work of Achar-Makisumi-Riche-Williamson,  one can calculate tilting characters of a reductive algebraic group
in positive characteristic p using the p-canonical/p-Kazhdan-Lusztig basis of the anti-spherical module. To calculate the p-Kazhdan-Lusztig basis one needs to calculate ranks of certain Hom-pairings (called intersection forms) in the diagrammatic Hecke category.
Unfortunately, string diagrams are well suited for calculations by hand, but how does one approach this problem using a computer?
I will explain an algorithm to calculate the p-canonical basis of the anti-spherical module (joint work with Geordie Williamson),
which allows to replicate the 10 months calculations Williamson performed for his Billiards conjecture in a couple of days.

Eric Katz, The Ohio State University

Coleman’s theory of p-adic integration is important for finding rational and torsion points on curves. An algorithm for computing Coleman integrals on good reduction hyperelliptic curves was introduced in work of Balakrishnan, Bradshaw, and Kedlaya and was refined by many others. We discuss work with Enis Kaya on extending this algorithm to bad reduction hyperelliptic curves. For bad reduction curves, there are two notions of p-adic integration: Berkovich–Coleman integrals which can be performed locally; and abelian integrals with desirable number-theoretic properties. We discuss how to compute Berkovich–Coleman integrals and then related them to abelian integrals by using tropical geometric techniques.

Yue Ren, Swansea University

Tropical varieties of neural networks [Slides]

In this talk, we introduce tropical varieties arising from neural networks with piecewise linear activations, and discuss how their geometry affects their expressivity. In particular, we will use Weibel’s f-Vector Theorem to derive optimal bounds for single-layered maxout networks, and Speyer’s f-Vector theorem to analyse networks with heavily restricted weights. We conclude with an initializing strategy for maxout networks based on our results.

Nicolas Thiéry, Université Paris Sud

Categories, axioms, constructions in SageMath: Modeling mathematics for fun and profit

The SageMath systems provides thousands of mathematical objects and tens of thousands of operations to compute with them. A system of this scale requires some infrastructure for writing and structuring generic code, documentation, and tests that apply uniformly on all objects within certain realms. In this talk, we describe the infrastructure implemented in SageMath. It is based on the standard object oriented features of Python, together with mechanisms to scale (dynamic classes, mixins, …) thanks to the rich available semantic (categories, axioms, constructions). We relate the approach taken with that in other systems (e.g. GAP), and discuss open problems.
This is meant as a basis for discussions: how are the equivalent challenges tackled in Oscar? Is there ground for crossfertilization!

Michael Stillman, Cornell University

Computational algebraic geometry, applications in string theory, and Macaulay2

In this talk we describe some open problems and interesting questions in computational algebraic geometry motivated by investigations in string theory, whose solutions would be useful to researchers in string theory. We describe recent work done in collaboration with Liam McAllister, Cody Long, Andreas Braun and others in this domain, and we keep it concrete by giving examples using Macaulay2.

Simon Brandhorst, Universität des Saarlandes

Equations for the K3-Lehmer map [Slides]

The dynamical complexity of an automorphism of a complex surface is measured by its topological entropy. The entropy is the logarithm of a Salem number, that is, a real algebraic integer $\lambda>1$ which is conjugate to $1/\lambda$ and all whose other conjugates lie on the unit circle. Conjecturally the smallest Salem number is Lehmer’s number $\lambda_{10}$. Lehmer’s conjecture is true for entropies: $\log(\lambda_{10})$ is the minimum among entropies of automorphisms of complex surfaces.
In a series of papers McMullen proved the existence of such an automorphism on a complex projective K3 surface. His strategy combines ideas from integer programming with the theory of lattices, number fields and reflection groups. The final step of the proof relies on the Torelli-type Theorem for K3 surfaces which is non constructive. In this talk I present equations for this automorphism. To find it we used Kneser’s neighbor method, elliptic fibrations and their linear systems, finite non-symplectic automorphisms and p-adic lifting.
This is joint work in progress with Noam D. Elkies.

Claus Fieker, TU Kaiserslautern

OSCAR: current, plans and dreams [Slides]

OSCAR is the next generation computer algebra system developed in the central software project of the SPP/ TRR 195. Written in the (rather young) Julia language, it combines the features and capabilities of Singular, Gap and Polymake with the newly created number theory package Hecke.
In this talk I will showcase some achievements, give an overview over the current status and indicate our current (immediate) plans and projects. I will conclude with some dreams about the longterm prospects.

Johannes Flake, RWTH Aachen

PBW deformations of smash products and computer algebra

PBW deformations of smash products form large classes of algebra deformations which include graded affine Hecke algebras, rational Cherednik algebras, symplectic reflection algebras, current Lie algebras, and many more of your favorite algebraic objects as special cases. I will explain how they can be studied from a general point of view, why some people find them interesting, why I find them interesting, and how I think computer algebra can help everybody to understand them better.

Anne Frühbis-Krüger, Universität Oldenburg

Zeta-functions, p-adic integrals and simultaneous monomialization

In this talk, we will discuss an approach to a class of order-zeta-functions through computation of p-adic integrals, whose domain of integration is rather far from being monomial. To render these integrals accessible to explicit computation, they need to be split up into a sum of simpler integrals. In our case the case distinction and simplification rely on a specific variant of resolution of singularities to obtain monomial condition on the domains of integration.

Laura Maaßen, RWTH Aachen

Interpolating Partition Categories [Slides]

In this talk we introduce tensor categories which interpolate the representation categories of partition quantum groups, which we view as subcategories of Deligne’s interpolation categories $\underline{\mathrm{Rep}(S_t)}$ for the symmetric groups. We compute the set of interpolation parameters yielding semisimple interpolation categories for all group-theoretical quantum groups, an uncountable family containing all but countably many partition quantum groups. A crucial ingredient is an abstract analysis of certain subobject lattices developed by Knop, which we adapt to categories of partitions.
We go on to present a parametrisation of the indecomposable objects for non-zero interpolation parameter using the representation theory for partition quantum groups developed by Freslon and Weber. This yields a description of the associated graded rings of the Grothendieck rings.
This is joint work with Johannes Flake.

Pascal Schweitzer, TU Kaiserslautern

Computing Symmetries: Isomorphism, Automorphism and Canonization of Graphs versus other Combinatorial Objects

The graph isomorphism problem, which asks for the existence of an isomorphism between two given finite input graphs, is known to be equivalent to the problem of computing automorphisms of graphs. One commonly applied method to solve this problem is via canonization.
In this talk I will relate the isomorphism problem of graphs to that of computing symmetries of other combinatorial objects. In fact there are general techniques to reinterpret finite combinatorial objects as graphs, while preserving their symmetry structure. This makes the graph isomorphism problem universal for isomorphism and automorphism problems of explicitly given combinatorial objects.
However, for implicitly given objects, such as those given by generating sets, the matter is different. Describing joint work with Daniel
Wiebking, the talks explains that a unified view of implicit combinatorial objects gives improved algorithms. This is in particular
the case for canonization algorithms and this view has subsequently also found applications in the computation of normalizers for permutation groups.

Andrea Thevis, Universität des Saarlandes

$p$-Origamis: Strata, Veech Groups and Sums of Lyapunov Exponents [Slides]

In this talk, we study a certain class of translation surfaces called $p$-origamis. These surfaces arise as normal covers of the torus with $p$-groups as deck transformation group. We classify the types of singularities of p-origamis and show that these depend in most cases only on the isomorphism class of the deck transformation group. For this, we use the rich theory of $p$-groups.
Veech groups of $p$-origamis are finite index subgroups of SL(2,Z) and capture a lot of information about the respective surfaces. We describe first results regarding Veech groups of $p$-origamis. Using these results, we compute the sum of Lyapunov exponents for certain example series of $p$-origamis.
This is partially joint work with Johannes Flake.

Gabriela Weitze-Schmithüsen, Universität des Saarlandes

Systoles on Origami Translation Surfaces [Slides]

A finite translation surface is a closed surface X together with the choice of a holomorphic differential. The moduli space of translation surfaces of genus g is stratified by the orders of the zeroes of the differentials.
Although translation surfaces have been intensively studied since the 1980’s, there are natural questions which are still wildly open. One of these questions is: Does there exist in each stratum a translation surface with a maximal systolic ratio, i.e. with a maximal shortest curve relative to the area. We study this question in the stratum H_2(1,1) of genus 2 surfaces with two zeroes of order 1. This is joint work with Columbus, Herrlich and Mützel.

Confirmed Participants

Total number: 107

Firoozeh Aga, Saarland University
Aslam Ali, TU Kaiserslautern
George Balla, RWTH Aachen
Mohamed Barakat, University of Siegen
Reimer Behrends, TU Kaiserslautern
Marc Bellon, CNRS et Sorbonne Université
Dominik Bernhardt, RWTH Aachen
Philippe Biane, CNRS, LIGM Université Paris Est
Janko Böhm, TU Kaiserslautern
Jendrik Brachter, TU Kaiserslautern
Simon Brandhorst, Saarland University
Jens Brandt, RWTH Aachen
Sofia Brenner, Friedrich-Schiller-Universität Jena
Thomas Breuer, RWTH Aachen University
Eirini Chavli, Universität Stuttgart
Michael Cuntz, Leibniz Universität Hannover
Wolfram Decker, TU Kaiserslautern
Tim Dokchitser, University of Bristol
Gérard Duchamp, Université Paris 13
Olivier Dudas, CNRS and Université de Paris
Holger Eble, TU Berlin
Kurusch Ebrahimi-Fard, Norwegian University of Science and Technology
Gavril Farkas, Humboldt-Universität zu Berlin
Claus Fieker, TU Kaiserslautern
Johannes Flake, RWTH Aachen
Anne Frühbis-Krüger, Universität Oldenburg
Nan Gao, Shanghai University
Sabrina Gaube, UOL / LUH
Meinolf Geck, University of Stuttgart
Christoph Goldner, Tübingen University
Pierre Guillot, Université de Strasbourg
Melanie Harms, RWTH Aachen University
William Hart, TU Kaiserslautern
Jonas Hetz, University of Stuttgart
Tommy Hofmann, Universität des Saarlandes
Johannes Hoffmann, Universität des Saarlandes
Max Horn, TU Kaiserslautern
Jens Hubrich, TU Kaiserslautern
Lars Thorge Jensen, Université Clermont Auvergne
Birte Johansson, TU Kaiserslautern
Pooja Joshi, IISER Bhopal
Kunda Kambaso, RWTH Aachen
Lars Kastner, TU Berlin
Eric Katz, The Ohio State University
Enis Kaya, University of Groningen
Hanieh Keneshlou, IMPAN
Matthias Klupsch, RWTH Aachen
Michael Kunte, TUK
Caroline Lassueur, TU Kaiserslautern
Felix Leid, Saarland University
Viktor Levandovskyy, RWTH Aachen
Benjamin Lorenz, TU Berlin
Frank Lübeck, RWTH Aachen
Laura Maaßen, RWTH Aachen University
Antonio Macchia, Freie Universität Berlin
Verity Mackscheidt, RWTH Aachen
Gunter Malle, TU Kaiserslautern
Dario Mathiä, University of Kaiserslautern
Aleksander Morgan, RWTH Aachen
Gabriele Nebe, RWTH Aachen University
Alice Niemeyer, RWTH Aachen
Emily Norton, TU Kaiserslautern
Gyan Datt Panday, PRSU, Prayagraj
Pierre-Guy Plamondon, Université Paris-Saclay
Sebastian Posur, RWTH Aachen
Ludwig Rahm, Norwegian University of Science and Technology NTNU
Iryna Raievska, Institute of Mathematics of National Academy of Sciences of Ukraine
Maryna Raievska, Institute of Mathematics of National Academy of Sciences of Ukraine
Yue Ren, Swansea University
Lukas Ristau, TU Kaiserslautern
Liam Rogel, TU Kaiserslautern
Emil Rotilio, TUK
Mahsa Sayyary Namin, MPI Leipzig
Johannes Schmitt, TU Kaiserslautern
Leonard Schmitz, RWTH Aachen
Hans Schönemann, TU Kaiserslautern
Mathias Schulze, TU Kaiserslautern
Pascal Schweitzer, TU Kaiserslautern
Farideh Shafiei, Institute for Research in Fundamental Sciences (IPM)
Vishal Shankhaval, Ganpat University
Farrokh Shirjian, Tarbiat Modares University
Carlo Sircana, TU Kaiserslautern
Roland Speicher, Saarland University
Mima Stanojkovski, Max-Planck-Institut fuer Mathematik in den Naturwissenschaften
Michael Stillman, Cornell University
Bernd Sturmfels, MPI Leipzig
Jayantha Suranimalee, TU Kaiserslautern
Melis Tekin Akcin, Hacettepe University
Nicolas Thiéry, Université Paris Sud
Ayush Kumar Tewari, TU Berlin
Andrea Thevis, Universität des Saarlandes
Ulrich Thiel, TU Kaiserslautern
Paul Vater, MPI MiS Leipzig
Claude Viallet, Centre National de la Recherche Scietntifique / Sorbonne Université
Laura Voggesberger, TU Kaiserslautern
Maria Walch, DFKI/IAV/TUK
Moritz Weber, Saarland University
Yvonne Weber, Technische Universität Kaiserslautern
Gabriela Weitze-Schmithüsen, Universität des Saarlandes
Oguzhan Yürük, TU Braunschweig
Eva Zerz, RWTH Aachen
Yinan Zhang, Australian National University

Contact

If you have any questions, please send an email to trr195-conference at mathematik.uni-kl.de.