Samuel German — Research
I work in theoretical computer science, especially graph theory, parameterized algorithms, and automata theory. A common theme in my work is obtaining exact structural characterizations, such as tractability and hardness thresholds for discrete problems and accepting-state spectra for automata operations.
I also care about teaching and mathematical exposition; I served for a year on the course staff for UC Berkeley’s CS 70, Discrete Mathematics and Probability Theory, first as an academic intern and then as a tutor.
Selected Publications
The Path-Extremal Conjecture for Zero Forcing: Distance-Hereditary Graphs and a Split-Decomposition Reduction
Samuel German.
Published in the Proceedings of the 32nd International Computing and Combinatorics Conference (COCOON 2026)
DOI
arXiv
Proves the zero-forcing path-extremal conjecture for distance-hereditary graphs and additionally uses canonical split decomposition to reduce the conjecture on an infinite class of graphs -- those with a unique prime bag of bounded size -- to finitely many checks on bounded-order split-prime cores.
Strong Conflict-Free Vertex-Connection via Twin Cover: Kernelization and Chromatic Bounds
Samuel German.
Published in the Proceedings of the 32nd International Computing and Combinatorics Conference (COCOON 2026)
DOI
arXiv
Gives a kernel for deciding whether the strong conflict-free vertex-connection number of
\(G\) is at most \(k\), parameterized by the twin-cover number of \(G\) and the target
number of colors \(k\). It also proves that for a twin cover \(X\), the strong
conflict-free vertex-connection number lies between the chromatic number \(\chi(G)\) and
\(\chi(G)+|X|\), and derives an exact formula for \(\chi(G)\) in terms of colorings
of \(G[X]\).
Layer-Based Width for PAFP
Samuel German.
Published in the Proceedings of the 37th International Workshop on Combinatorial Algorithms (IWOCA 2026)
DOI
Introduces layer-based width parameters for the Path Avoiding Forbidden Pairs problem via both the union digraph
\(G \cup \mathcal{F}\) and the input graph \(G\), and proves a sharp union-digraph contrast:
bounded union BFS-width together with bounded backward arcs yields an FPT algorithm, whereas
bounded union BFS-width alone remains \(\mathsf{NP}\text{-}\)hard already at width \(2\).
On the input-graph side, it gives the first tractability regimes for PAFP with unrestricted
forbidden pairs, including FPT for BFS-width \(2\) with bounded backward input arcs
and polynomial time for exact-length width \(2\), both of which results, the paper shows, are tight against width-\(3\) hardness.