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Documents authored by Gerhard, Enna

Document
DOI: 10.4230/LIPIcs.MFCS.2026.82
Separating Feasibility and Movement in Solution Discovery: The Case of Path Discovery

Authors: Hanno von Bergen, Larissa Fastenau, Enna Gerhard, Nicola Lorenz, Stephanie Maaz, Amer E. Mouawad, Roman Rabinovich, Nicole Schirrmacher, Daniel Schmand, Sebastian Siebertz, and Mai Trinh

Published in: LIPIcs, Volume 386, 51st International Symposium on Mathematical Foundations of Computer Science (MFCS 2026)

Abstract
We study solution discovery, where the goal is to obtain a feasible solution to a problem from an initial configuration by a bounded sequence of local moves. In many applications, however, the graph that defines which vertex sets are feasible is not the same as the graph that governs how tokens, agents, or resources may move. Existing models such as token sliding and token jumping typically do not distinguish the problem graph and the movement graph. Motivated by this mismatch, we introduce a directed weighted two-graph model that cleanly separates feasibility from movement. A problem graph specifies the desired combinatorial objects, while a movement graph specifies admissible relocations and their costs. This yields a flexible framework that captures asymmetry, heterogeneous movement constraints, and weighted transitions, while subsuming classical discovery models as special cases. We investigate this model through Path Discovery and Shortest Path Discovery, where the task is to realize a vertex set containing an s-t-path or a shortest s-t-path in the problem graph. These problems are particularly natural in applications, since directed and weighted shortest paths are among the most fundamental algorithmic primitives. At the same time, previous work has already shown that discovery can be computationally hard even when the underlying optimization problem is easy. Our results show that this phenomenon persists, and becomes especially rich, in the two-graph setting. We obtain a detailed complexity picture, identifying tractable cases as well as strong hardness results.
Cite as

Hanno von Bergen, Larissa Fastenau, Enna Gerhard, Nicola Lorenz, Stephanie Maaz, Amer E. Mouawad, Roman Rabinovich, Nicole Schirrmacher, Daniel Schmand, Sebastian Siebertz, and Mai Trinh. Separating Feasibility and Movement in Solution Discovery: The Case of Path Discovery. In 51st International Symposium on Mathematical Foundations of Computer Science (MFCS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 386, pp. 82:1-82:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{vonbergen_et_al:LIPIcs.MFCS.2026.82,
  author =	{von Bergen, Hanno and Fastenau, Larissa and Gerhard, Enna and Lorenz, Nicola and Maaz, Stephanie and Mouawad, Amer E. and Rabinovich, Roman and Schirrmacher, Nicole and Schmand, Daniel and Siebertz, Sebastian and Trinh, Mai},
  title =	{{Separating Feasibility and Movement in Solution Discovery: The Case of Path Discovery}},
  booktitle =	{51st International Symposium on Mathematical Foundations of Computer Science (MFCS 2026)},
  pages =	{82:1--82:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-442-0},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{386},
  editor =	{Kouck\'{y}, Michal and Petrișan, Daniela},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2026.82},
  URN =		{urn:nbn:de:0030-drops-274646},
  doi =		{10.4230/LIPIcs.MFCS.2026.82},
  annote =	{Keywords: solution discovery, shortest path discovery, token sliding, parameterized complexity}
}
Artifact
Software
DOI: 10.4230/artifacts.25239
OBLX

Authors: Jona Dirks, Enna Gerhard, Victoria Kaial, and Lucas Lorieau

Abstract
Cite as

Jona Dirks, Enna Gerhard, Victoria Kaial, Lucas Lorieau. OBLX (Software, Source Code). Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@misc{dagstuhl-artifact-25239,
   title = {{OBLX}}, 
   author = {Dirks, Jona and Gerhard, Enna and Kaial, Victoria and Lorieau, Lucas},
   note = {Software, swhId: \href{https://archive.softwareheritage.org/swh:1:dir:2863e5f060c85b6d04b04c053ab39135abee8f0d;origin=https://gitlab.limos.fr/oblx/public;visit=swh:1:snp:978f34493f4e2e5a17e1ac4277e892ce7ab64cef;anchor=swh:1:rev:75b59b41ff96536dcb36f5b677ed1fa5ad2d041c}{\texttt{swh:1:dir:2863e5f060c85b6d04b04c053ab39135abee8f0d}} (visited on 2025-12-15)},
   url = {https://gitlab.limos.fr/oblx/public},
   doi = {10.4230/artifacts.25239},
}
Document
PACE Solver Description
DOI: 10.4230/LIPIcs.IPEC.2025.33
PACE Solver Description: OBLX Exact Solver for the Dominating Set Problem

Authors: Jona Dirks, Enna Gerhard, Victoria Kaial, and Lucas Lorieau

Published in: LIPIcs, Volume 358, 20th International Symposium on Parameterized and Exact Computation (IPEC 2025)

Abstract
We present and describe the solver OBLX for the Dominating Set problem on graphs. This solver was developed during the PACE challenge 2025 for the Exact track. It first applies several data reduction rules and performs a polynomial time reduction to Max Sat. The resulting Max Sat instance is in turn solved using the EvalMaxSat solver by Florent Avellaneda.
Cite as

Jona Dirks, Enna Gerhard, Victoria Kaial, and Lucas Lorieau. PACE Solver Description: OBLX Exact Solver for the Dominating Set Problem. In 20th International Symposium on Parameterized and Exact Computation (IPEC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 358, pp. 33:1-33:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{dirks_et_al:LIPIcs.IPEC.2025.33,
  author =	{Dirks, Jona and Gerhard, Enna and Kaial, Victoria and Lorieau, Lucas},
  title =	{{PACE Solver Description: OBLX Exact Solver for the Dominating Set Problem}},
  booktitle =	{20th International Symposium on Parameterized and Exact Computation (IPEC 2025)},
  pages =	{33:1--33:4},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-407-9},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{358},
  editor =	{Agrawal, Akanksha and van Leeuwen, Erik Jan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2025.33},
  URN =		{urn:nbn:de:0030-drops-251659},
  doi =		{10.4230/LIPIcs.IPEC.2025.33},
  annote =	{Keywords: complexity theory, parameterized complexity, linear programming, java, dominating set, PACE 2025}
}
Document
PACE Solver Description
DOI: 10.4230/LIPIcs.IPEC.2022.30
PACE Solver Description: GraPA-JAVA

Authors: Moritz Bergenthal, Jona Dirks, Thorben Freese, Jakob Gahde, Enna Gerhard, Mario Grobler, and Sebastian Siebertz

Published in: LIPIcs, Volume 249, 17th International Symposium on Parameterized and Exact Computation (IPEC 2022)

Abstract
We present an exact solver for the DFVS, submitted for the exact track of the Parameterized Algorithms and Computational Experiments challenge (PACE) in 2022. The solver heavily relies on data reduction (known from the literature and new reduction rules). The instances are then further processed by integer linear programming approaches. We implemented the algorithm in the scope of a student project at the University of Bremen.
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Moritz Bergenthal, Jona Dirks, Thorben Freese, Jakob Gahde, Enna Gerhard, Mario Grobler, and Sebastian Siebertz. PACE Solver Description: GraPA-JAVA. In 17th International Symposium on Parameterized and Exact Computation (IPEC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 249, pp. 30:1-30:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bergenthal_et_al:LIPIcs.IPEC.2022.30,
  author =	{Bergenthal, Moritz and Dirks, Jona and Freese, Thorben and Gahde, Jakob and Gerhard, Enna and Grobler, Mario and Siebertz, Sebastian},
  title =	{{PACE Solver Description: GraPA-JAVA}},
  booktitle =	{17th International Symposium on Parameterized and Exact Computation (IPEC 2022)},
  pages =	{30:1--30:4},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-260-0},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{249},
  editor =	{Dell, Holger and Nederlof, Jesper},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2022.30},
  URN =		{urn:nbn:de:0030-drops-173861},
  doi =		{10.4230/LIPIcs.IPEC.2022.30},
  annote =	{Keywords: complexity theory, parameterized complexity, linear programming, java, directed feedback vertex set, PACE 2022}
}

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