Christian Laußmann

Computer scientist at the Heinrich-Heine-University Düsseldorf.

Interests

Computational social choice • cryptography • crypto currencies and distributed ledger • programming • IT security • computational complexity theory • space

Hobbies

Latin dancing • YouTube creator • Insects

Research

I mostly do research in the area of Computational Social Choice. In this research area we are interested in the design and analysis of methods for collective decision making. Particularly, my research is focused on multiwinner voting rules, apportionment methods for parliamentary elections, and participatory budgeting. See the following list of my recent publications.

ULB Düsseldorf	COMSOC Methods in Real-World Applications • Christian Laussmann • My dissertation containing my studies on network centrality through voting rules, participatory budgeting under uncertainty, apportionment elections, and bounded approval ballots.

AAMAS-2023	Bounded Approval Ballots: Balancing Expressiveness and Simplicity for Multiwinner Elections • Dorothea Baumeister, Linus Boes, Christian Laussmann, and Simon Rey • Approval ballots are often used for multiwinner elections because they are particularly simple to use. However, their expressiveness lacks e.g. substitution effects or dependencies between candidates. We propose and analyze an extension to approval ballots which gives the voters more options to express what they really want to express while not increasing the cognitive burden much. In fact, simple approval ballots are still valid, so for a lazy voter submitting a preference is no more difficult than submitting an approval ballot.

IJCAI-2022	Time-Constrained Participatory Budgeting Under Uncertain Project Costs • Dorothea Baumeister, Linus Boes, and Christian Laussmann • We show that planing a participatory budgeting campaign under uncertainty in the costs of projects is a very difficult process. After proving that no optimal algorithms exist, we develop best-effort algorithms which we were able to show perform well on average instances. (Link to video)

AAMAS-2022	Voting for Centrality (extended abstract) • Ulrik Brandes, Christian Laussmann, and Jörg Rothe • Voting rules are methods from social choice theory to determine the winners according to preferences of voters. We propose to interpret network relations (e.g. distances) as preferences. Using these preferences, we can rank nodes in the network by their centrality using voting rules.

Programming Projects and Contributions

2022 - 2023	GoodVoteX is a web application which helps people make better collective decisions. To this end, we have implemented several common ballot formats and voting rules for both multiwinner and single-winner elections. When creating an election, the user can decide which configuration to use, with recommendations from the system. GoodVoteX is open source and runs in a docker container.

Teaching

2023	Fair Division • A master course about fair division procedures. We cover cake-cutting, and fair division of indivisible goods. I prepared exercise sheets and offered a practice group.

2020 - 2023	Preliminary Course Computer Science • The preliminary course introduces new computer science students to the university. The course focuses on basics of math, logic, and programming. I co-organized the course, decided contents, prepared materials, and taught parts of the students.

2022	Co-Organizer of EUMAS Conference • The European Conference on Multi-Agent Systems (EUMAS) is an EURAMAS designated event which attracts researchers from all over Europe but also everywhere in the world. I organized the PhD Day which includes presentations and working groups for PhD students.

2022	Theoretical Computer Science • A mandatory bachelor course about an introduction to all areas of theoretical computer science. I prepared exercise sheets and offered a practice group.

2021	Girls-Day Computer Science at HHU • The Girls Day is a short seminar for girls in junior high, and high school. We give an impression what the job as researcher in computer science is like. I prepared materials about cryptology and co-organized the day.