Algorithms & Complexity

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New Paper in ACM Transactions on Computation Theory 18 Feb 2026

Trading claims of a bank in distress is described in, e.g., the U.S. and E.U. banking regulations. We formalize this notion in the context of financial networks and study its algorithmic properties. Our paper "Algorithms for Claims Trading" (by Martin Hoefer, Carmine Ventre, Lisa Wilhelmi) characterizes structural properties, provides efficient (approximation) algorithms to compute optimal claims trades, and shows complementing computational hardness results in several variants. Our results reveal an interesting dichotomy -- optimal trading of claims with a common creditor is algorithmically much easier than trading claims with a common debtor. The paper has been accepted for publication in ACM Transactions on Computation Theory.

New Paper in Theoretical Computer Science 12 Feb 2026

In our paper "The Complexity of Blocking All Solutions" (by Christoph Grüne, Lasse Wulf) we consider a general problem of blocking all solutions of some given combinatorial problem with only few elements. This includes, for example, the problem of destroying all Hamiltonian cycles of a given graph by forbidding only few edges; or the problem of destroying all maximum cliques of a given graph by forbidding only few vertices. For a large class of these problems we show that they are Σ₂^p-complete. Thus, they are substantially more difficult (under standard assumptions in complexity theory) than the underlying base problems (e.g., deciding existence of a Hamiltonian path or finding a maximum clique). The paper has been accepted for publication in Theoretical Computer Science.

Dissertation Defense 9 Feb 2025

Our former group member Komal Muluk successfully defended her thesis entitled Computational Complexity of Graph Orientation, Bilevel and Robust Optimization Problems. Congratulations to Dr. Muluk!

New Paper in Theoretical Computer Science 28 Jan 2026

Debt swaps are a novel local adjustment step to increase the stability and clearing properties of financial networks. In our paper "Dynamic Debt Swapping in Financial Networks" (by Henri Froese, Lisa Wilhelmi, Martin Hoefer) we analyze structural properties and computational complexity of sequential debt swapping. We bound the length of debt swap sequences and examine the hardness of computing states from which no (profitable) debt swap exists. Depending on the payment functions of the banks and the improvement properties of the swaps, we obtain polynomial bounds or establish PLS- and PSPACE-hardness results. The paper has been accepted for publication in Theoretical Computer Science.

New Paper in Algorithms for Molecular Biology 21 Jan 2026

Transcription factors (TFs) are essential in the regulation of gene expression. They can be used to address diseases via manipulation of specific cell functions or pathways. The interplay of TFs and genes can be modeled as a network, in which each edge represents a regulatory influence. A challenge is the identification of a set of TFs with the maximum regulatory influence. In our paper "Probing transcription factor subsets in gene regulatory networks" (by Lukas Geis, Dennis Hecker, Martin Hoefer, Ulrich Meyer, Marcel Schulz) we study finding a set of TFs to maximize the influence on a set of genes as a probing problem in a bipartite graph. We analyze different adaptive and non-adaptive algorithms and test their performance on real-life data to find TFs regulating genes involved in T-cell mediated immunity and lymphoid leukemia. The paper has been accepted for publication in Algorithms for Molecular Biology.

Welcome 1 Jan 2026

Svenja Griesbach joined our group as a PostDoc. Welcome, Svenja!