Sebastian Wiederrecht

Changing a given configuration in a graph into another one is known as a reconfiguration problem. Such problems have recently received much interest in the context of algorithmic graph theory. We initiate the theoretical study of the following reconfiguration problem: How to reroute k unsplittable flows of a certain demand in a capacitated network from their current paths to their respective new paths, in a congestion-free manner? This problem finds immediate applications, e.g., in traffic engin

Changing a given configuration in a graph into another one is known as a re- configuration problem. Such problems have recently received much interest in the context of algorithmic graph theory. We initiate the theoretical study of the following reconfiguration problem: How to reroute $k$ unsplittable flows of a certain demand in a capacitated network from their current paths to their respective new paths, in a congestion-free manner? This problem finds immediate applications, e.g., in traffic e

A colouring of a digraph as defined by Neumann-Lara in 1982 is a vertex-colouring such that no monochromatic directed cycles exist. The minimal number of colours required for such a colouring of a loopless digraph is defined to be its dichromatic number. This quantity has been widely studied in the last decades and can be considered as a natural directed analogue of the chromatic number of a graph. A digraph $D$ is called even if for every $0$-$1$-weighting of the edges it contains a directed cy

The branchwidth of a graph has been introduced by Roberson and Seymour as a measure of the tree-decomposability of a graph, alternative to treewidth. Branchwidth is polynomially computable on planar graphs by the celebrated ``Ratcatcher'' algorithm of Seymour and Thomas. We explore how this algorithm can be extended to minor-closed graph classes beyond planar graphs, as follows: Let $H_{1}$ be a graph embeddable in the torus and $H_{2}$ be a graph embeddable in the projective plane. We prove tha

We consider the SDN network update problem in which a controller wants to update the routes of k (unsplittable) flows from their old paths to the new paths, consistently, i.e., without temporary congestion. As updates communicated by the controller take effect asynchronously, the challenge is to perform these updates fast, i.e., using a minimal number of rounds (controller interactions). We present the first fast, i.e., polynomial-time solution for scheduling such congestion-free network updates

We consider the SDN network update problem in which a controller wants to update the routes of k (unsplittable) flows from their old paths to the new paths, consistently, i.e., without temporary congestion. As updates communicated by the controller take effect asynchronously, the challenge is to perform these updates fast, i.e., using a minimal number of rounds (controller interactions). We present the first fast, i.e., polynomial-time solution for scheduling such congestion-free network updates

By a seminal result of Valiant, computing the permanent of (0,1)-matrices is, in general, #P-hard. In 1913 Polya asked for which (0,1)-matrices A it is possible to change some signs such that the permanent of A equals the determinant of the resulting matrix. In 1975, Little showed these matrices to be exactly the biadjacency matrices of bipartite graphs excluding K3,3 as a matching minor. This was turned into a polynomial time algorithm by McCuaig, Robertson, Seymour, and Thomas in 1999. However

Let <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathcal{G}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathcal{H}$</tex> be minor-closed graph classes. We say that the pair <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathcal{H},\ \mathcal{G})$</tex> is an Erdös-Pósa pair (EP-pair) if there exists a function <tex xmlns:mml="http

Many recent works address the question of characterizing induced obstructions to bounded treewidth. In 2022, Lozin and Razgon completely answered this question for graph classes defined by finitely many forbidden induced subgraphs. Their result also implies a characterization of graph classes defined by finitely many forbidden induced subgraphs that are $(tw,ω)$-bounded, that is, treewidth can only be large due to the presence of a large clique. This condition is known to be satisfied for any gr