Who am I ?

I am an ATER in Paris University. Before that, I was a postdoc at Charles University, and even before that, I was a PhD student under the supervision of Pierre Aboulker and Pierre Charbit in the TALGO team at École Normale Supérieure and in the IRIF lab at Paris University. I’m mainly interested in graph theory, optimization and algorithmics, and I’m fond of algorithmic contests.

In a past life, I have worked for almost two years as a Google Software Engineer in Zürich, Switzerland, and have attended École Normale Supérieure Paris-Saclay before that.

Why are you here ?

Research

My research interests revolve around graph theory, in particular directed graph theory. I focus on digraph colouring, a notion which arised lately and consists in partitioning directed graphs into acyclic subgraphs. You can find my PhD thesis here.

I am an author of the following published papers and preprint:

• Finding forest-orderings of tournaments is NP-complete, whose preprint is on arXiv.
• Computing the clique number of tournaments, whose preprint is on arXiv.
• Clique number of tournaments, joint work with Pierre Aboulker, Pierre Charbit and Raul Lopes, whose preprint is on arXiv.
• Digraph Colouring and Arc-Connectivity, joint work with Pierre Aboulker and Pierre Charbit, whose preprint is on arXiv,
• Problems, proofs, and disproofs on the inversion number, joint work with Frédéric Havet, Florian Hörsch, Felix Klingelhoefer, Nicolas Nisse, Clément Rambaud and Quentin Vermande, whose preprint is on arXiv,
• (P6, triangle)-free digraphs have bounded dichromatic number, joint work with Pierre Aboulker, Pierre Charbit and Stéphan Thomassé, whose preprint is on arXiv,
• Vizing’s and Shannon’s Theorems for defective edge colouring, joint work with Pierre Aboulker and Chien-Chung Huang, published in Electronic Journal of Combinatorics (DOI),
• Heroes in orientations of chordal graphs, joint work with Pierre Aboulker and Raphael Steiner, published in SIAM Journal of Discrete Mathematics (DOI),
• Heroes in oriented complete multipartite graphs, joint work with Pierre Aboulker and Pierre Charbit, published in Journal of Graph Theory (DOI),
• Decomposing and colouring some locally semicomplete digraphs, joint work with Pierre Aboulker and Pierre Charbit, published in European Journal of Combinatorics (DOI),
• Four proofs of the directed Brooks’ theorem, joint work with Pierre Aboulker, published in Discrete Mathematics (DOI) – Editor’s choice 2024.

I have also presented in the following conferences and workshops :

• JGA 2020, presenting Brooks’ theorem on digraphs
• ANR Digraphs 2021, presenting a Decomposition theorem for locally in-transitive tournaments
• EUROCOMB’21, presenting Decomposing and Colouring Locally Out-Transitive Oriented Graphs
• JGA 2021, presenting Vizing’s and Shannon’s Theorems for edge-defective colouring
• ICGT 2022, presenting Heroes in Orientations of Complete Multipartite Graphs
• JGA 2022, presenting (P_6, triangle)-free digraphs have bounded dichromatic number
• ANR Digraphs 2023, presenting Maximum local arc-connectivity and dichromatic number
• Charles University seminars, presenting Colouring Digraphs
• Séminaire Bordeaux 2024, présenting Clique number of tournaments
• JGA 2024, presenting Des graphes sans triangle de grand nombre chromatique

I was in the organizing committee of JGA 2022, along with Pierre Aboulker and Thomas Bellitto.

Teaching

This year, I am responsible at Paris University: * of the course and practical works for Elements of algorithms (L2) * of the course Algorithms (M1) * of Project tutoring (M1) * of the course and practical works for Initiation to C programming (L3 maths)

In the last case, I am the only person in charge, and you can find further information of the dedicated page.

I have been responsible for the tutorials at Charles University for Combinatorics and Graph Theory III. List of exercise sheets:

• Exercise sheet 1
• Exercise sheet 2
• Exercise sheet 3
• Exercise sheet 4
• Exercise sheet 5
• Exercise sheet 6
• Exercise sheet 7
• Exercise sheet 8
• Exercise sheet 9

And here is the homework to handout by November 30:

• Homework

Before that, I was a teaching fellow at Paris University. I have been in charge of :

• Practical works for Initiation to Python Programming (IP1 Python) in 2020-2021 and 2022-2023
• Practical works for Web and tools (IO2 Internet et Outils) in 2020-2021
• Practical works for Initiation to Java Programming (IP1 Java) in 2021-2022 and 2022-2023
• Practical and theoretical works for Principles of operation of binary machines (PF1 Principes de fonctionnement des machines binaires) in 2021-2022
• Practical works for Introduction to Operating Systems (IS1 Initiation aux Systèmes d’Exploitation) in 2022-2023

Algorithmic Contests

Since 2023, I am a judge at ICPC SWERC, and before that I was a coach for ENS Paris-Saclay (and a contestant before that).

I used to train on Codeforces, currently am ranked master, and hope to someday get the motivation to get to grandmaster. I have alse reached twice the third round of Google Code Jam, once the offline finals of Google Hash Code, have won two editions of Battle Dev and also have won Codin’Night.

How to contact me ?

My mail address is firstname.lastname@gaubian.xyz but you can also contact me on Discord under username LeCaRiBoU#3837 or aubian on irc.{rezosup.org, freenode.net, ulminfo.fr}.