7 Search Results for "Joswig, Michael"

Document
DOI: 10.4230/LIPIcs.SoCG.2026.85
ETH-Tight Complexity of Optimal Morse Matching on Bounded-Treewidth Complexes

Authors: Geevarghese Philip and Erlend Raa Vågset

Published in: LIPIcs, Volume 367, 42nd International Symposium on Computational Geometry (SoCG 2026)

Abstract
The Optimal Morse Matching (OMM) problem asks for a discrete gradient vector field on a simplicial complex that minimizes the number of critical simplices. It is NP-hard and has been studied extensively in heuristic, approximation, and parameterized complexity settings. Parameterized by treewidth k, OMM has long been known to be solvable on triangulations of 3-manifolds in 2^O(k²) n^O(1) time and in FPT time for triangulations of arbitrary manifolds, but the exact dependence on k has remained an open question. We resolve this by giving a new 2^O(k log k) n-time algorithm for any finite regular CW complex, and show that no 2^o(k log k) n^O(1)-time algorithm exists unless the Exponential Time Hypothesis (ETH) fails.
Cite as

Geevarghese Philip and Erlend Raa Vågset. ETH-Tight Complexity of Optimal Morse Matching on Bounded-Treewidth Complexes. In 42nd International Symposium on Computational Geometry (SoCG 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 367, pp. 85:1-85:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

Copy BibTex To Clipboard

@InProceedings{philip_et_al:LIPIcs.SoCG.2026.85,
  author =	{Philip, Geevarghese and V\r{a}gset, Erlend Raa},
  title =	{{ETH-Tight Complexity of Optimal Morse Matching on Bounded-Treewidth Complexes}},
  booktitle =	{42nd International Symposium on Computational Geometry (SoCG 2026)},
  pages =	{85:1--85:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-418-5},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{367},
  editor =	{Ahn, Hee-Kap and Hoffmann, Michael and Nayyeri, Amir},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2026.85},
  URN =		{urn:nbn:de:0030-drops-258926},
  doi =		{10.4230/LIPIcs.SoCG.2026.85},
  annote =	{Keywords: Discrete Morse Theory, Simplicial Complexes, Optimal Morse Matching, Treewidth, Parameterized Algorithms, Computational Topology, Dynamic Programming, Exponential Time Hypothesis, Topological Data Analysis}
}
Document
DOI: 10.4230/LIPIcs.STACS.2026.31
Lower Bounds for Ranking-Based Pivot Rules

Authors: Yann Disser, Georg Loho, Matthew Maat, and Nils Mosis

Published in: LIPIcs, Volume 364, 43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026)

Abstract
The existence of a polynomial pivot rule for the simplex method for linear programming, policy iteration for Markov decision processes, and strategy improvement for parity games each are prominent open problems in their respective fields. While numerous natural candidates for efficient rules have been eliminated, all existing lower bound constructions are tailored to individual or small sets of pivot rules. We introduce a unified framework for formalizing classes of rules according to the information about the input that they rely on. Within this framework, we show lower bounds for ranking-based classes of rules that base their decisions on orderings of the improving pivot steps induced by the underlying data. Our first result is a superpolynomial lower bound for strategy improvement, obtained via a family of sink parity games, which applies to memory-based generalizations of Bland’s rule that only access the input by comparing the ranks of improving edges in some global order. Our second result is a subexponential lower bound for policy iteration, obtained via a family of Markov decision processes, which applies to memoryless rules that only access the input by comparing improving actions according to their ranks in a global order, their reduced costs, and the associated improvements in objective value. Both results carry over to the simplex method for linear programming.
Cite as

Yann Disser, Georg Loho, Matthew Maat, and Nils Mosis. Lower Bounds for Ranking-Based Pivot Rules. In 43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 364, pp. 31:1-31:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

Copy BibTex To Clipboard

@InProceedings{disser_et_al:LIPIcs.STACS.2026.31,
  author =	{Disser, Yann and Loho, Georg and Maat, Matthew and Mosis, Nils},
  title =	{{Lower Bounds for Ranking-Based Pivot Rules}},
  booktitle =	{43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026)},
  pages =	{31:1--31:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-412-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{364},
  editor =	{Mahajan, Meena and Manea, Florin and McIver, Annabelle and Thắng, Nguy\~{ê}n Kim},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2026.31},
  URN =		{urn:nbn:de:0030-drops-255207},
  doi =		{10.4230/LIPIcs.STACS.2026.31},
  annote =	{Keywords: lower bounds, Markov decision processes, parity games, pivot rules, policy iteration, simplex method}
}
Document
DOI: 10.4230/OASIcs.ATMOS.2025.2
A Geometric Approach to Integrated Periodic Timetabling and Passenger Routing

Authors: Fabian Löbel and Niels Lindner

Published in: OASIcs, Volume 137, 25th Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2025)

Abstract
We offer a geometric perspective on the problem of integrated periodic timetabling and passenger routing in public transport. Inside the space of periodic tensions, we single out those regions, where the same set of paths provides shortest passenger routes. This results in a polyhedral subdivision, which we combine with the known decomposition by polytropes. On each maximal region of the common refinement, the integrated problem is solvable in polynomial time. We transform these insights into a new geometry-driven primal heuristic, integrated tropical neighborhood search (ITNS). Computationally, we compare implementations of ITNS and the integrated (restricted) modulo network simplex algorithm on the TimPassLib benchmark set, and contribute better solutions in terms of total travel time for all but one of the twenty-five instances for which a proven optimal solution is not yet known.
Cite as

Fabian Löbel and Niels Lindner. A Geometric Approach to Integrated Periodic Timetabling and Passenger Routing. In 25th Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2025). Open Access Series in Informatics (OASIcs), Volume 137, pp. 2:1-2:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

Copy BibTex To Clipboard

@InProceedings{lobel_et_al:OASIcs.ATMOS.2025.2,
  author =	{L\"{o}bel, Fabian and Lindner, Niels},
  title =	{{A Geometric Approach to Integrated Periodic Timetabling and Passenger Routing}},
  booktitle =	{25th Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2025)},
  pages =	{2:1--2:19},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-404-8},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{137},
  editor =	{Sauer, Jonas and Schmidt, Marie},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ATMOS.2025.2},
  URN =		{urn:nbn:de:0030-drops-247580},
  doi =		{10.4230/OASIcs.ATMOS.2025.2},
  annote =	{Keywords: Periodic Timetabling, Passenger Routing, Polyhedral Complexes}
}
Document
DOI: 10.4230/LIPIcs.SoCG.2020.67
Connectivity of Triangulation Flip Graphs in the Plane (Part II: Bistellar Flips)

Authors: Uli Wagner and Emo Welzl

Published in: LIPIcs, Volume 164, 36th International Symposium on Computational Geometry (SoCG 2020)

Abstract
Given a finite point set P in general position in the plane, a full triangulation is a maximal straight-line embedded plane graph on P. A partial triangulation on P is a full triangulation of some subset P' of P containing all extreme points in P. A bistellar flip on a partial triangulation either flips an edge, removes a non-extreme point of degree 3, or adds a point in P ⧵ P' as vertex of degree 3. The bistellar flip graph has all partial triangulations as vertices, and a pair of partial triangulations is adjacent if they can be obtained from one another by a bistellar flip. The goal of this paper is to investigate the structure of this graph, with emphasis on its connectivity. For sets P of n points in general position, we show that the bistellar flip graph is (n-3)-connected, thereby answering, for sets in general position, an open questions raised in a book (by De Loera, Rambau, and Santos) and a survey (by Lee and Santos) on triangulations. This matches the situation for the subfamily of regular triangulations (i.e., partial triangulations obtained by lifting the points and projecting the lower convex hull), where (n-3)-connectivity has been known since the late 1980s through the secondary polytope (Gelfand, Kapranov, Zelevinsky) and Balinski’s Theorem. Our methods also yield the following results (see the full version [Wagner and Welzl, 2020]): (i) The bistellar flip graph can be covered by graphs of polytopes of dimension n-3 (products of secondary polytopes). (ii) A partial triangulation is regular, if it has distance n-3 in the Hasse diagram of the partial order of partial subdivisions from the trivial subdivision. (iii) All partial triangulations are regular iff the trivial subdivision has height n-3 in the partial order of partial subdivisions. (iv) There are arbitrarily large sets P with non-regular partial triangulations, while every proper subset has only regular triangulations, i.e., there are no small certificates for the existence of non-regular partial triangulations (answering a question by F. Santos in the unexpected direction).
Cite as

Uli Wagner and Emo Welzl. Connectivity of Triangulation Flip Graphs in the Plane (Part II: Bistellar Flips). In 36th International Symposium on Computational Geometry (SoCG 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 164, pp. 67:1-67:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

Copy BibTex To Clipboard

@InProceedings{wagner_et_al:LIPIcs.SoCG.2020.67,
  author =	{Wagner, Uli and Welzl, Emo},
  title =	{{Connectivity of Triangulation Flip Graphs in the Plane (Part II: Bistellar Flips)}},
  booktitle =	{36th International Symposium on Computational Geometry (SoCG 2020)},
  pages =	{67:1--67:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-143-6},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{164},
  editor =	{Cabello, Sergio and Chen, Danny Z.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2020.67},
  URN =		{urn:nbn:de:0030-drops-122259},
  doi =		{10.4230/LIPIcs.SoCG.2020.67},
  annote =	{Keywords: triangulation, flip graph, graph connectivity, associahedron, subdivision, convex decomposition, flippable edge, flip complex, regular triangulation, bistellar flip graph, secondary polytope, polyhedral subdivision}
}
Document
Multimedia Contribution
DOI: 10.4230/LIPIcs.SoCG.2017.66
MatchTheNet - An Educational Game on 3-Dimensional Polytopes (Multimedia Contribution)

Authors: Michael Joswig, Georg Loho, Benjamin Lorenz, and Rico Raber

Published in: LIPIcs, Volume 77, 33rd International Symposium on Computational Geometry (SoCG 2017)

Abstract
We present an interactive game which challenges a single player to match 3-dimensional polytopes to their planar nets. It is open source, and it runs in standard web browsers.
Cite as

Michael Joswig, Georg Loho, Benjamin Lorenz, and Rico Raber. MatchTheNet - An Educational Game on 3-Dimensional Polytopes (Multimedia Contribution). In 33rd International Symposium on Computational Geometry (SoCG 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 77, pp. 66:1-66:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

Copy BibTex To Clipboard

@InProceedings{joswig_et_al:LIPIcs.SoCG.2017.66,
  author =	{Joswig, Michael and Loho, Georg and Lorenz, Benjamin and Raber, Rico},
  title =	{{MatchTheNet - An Educational Game on 3-Dimensional Polytopes}},
  booktitle =	{33rd International Symposium on Computational Geometry (SoCG 2017)},
  pages =	{66:1--66:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-038-5},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{77},
  editor =	{Aronov, Boris and Katz, Matthew J.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2017.66},
  URN =		{urn:nbn:de:0030-drops-72435},
  doi =		{10.4230/LIPIcs.SoCG.2017.66},
  annote =	{Keywords: three-dimensional convex polytopes, unfoldings}
}
Document
DOI: 10.4230/DagRep.6.11.168
Algorithms and Effectivity in Tropical Mathematics and Beyond (Dagstuhl Seminar 16482)

Authors: Stéphane Gaubert, Dima Grigoriev, Michael Joswig, and Thorsten Theobald

Published in: Dagstuhl Reports, Volume 6, Issue 11 (2017)

Abstract
This report documents the Dagstuhl Seminar on Algorithms and Effectivity in Tropical Mathematics and Beyond, which took place from November 27 -- December 02, 2016. The report contains an executive summary as well as abstracts of the talks which reflect recent progress in the topic of the meeting.
Cite as

Stéphane Gaubert, Dima Grigoriev, Michael Joswig, and Thorsten Theobald. Algorithms and Effectivity in Tropical Mathematics and Beyond (Dagstuhl Seminar 16482). In Dagstuhl Reports, Volume 6, Issue 11, pp. 168-184, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

Copy BibTex To Clipboard

@Article{gaubert_et_al:DagRep.6.11.168,
  author =	{Gaubert, St\'{e}phane and Grigoriev, Dima and Joswig, Michael and Theobald, Thorsten},
  title =	{{Algorithms and Effectivity in Tropical Mathematics and Beyond (Dagstuhl Seminar 16482)}},
  pages =	{168--184},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2017},
  volume =	{6},
  number =	{11},
  editor =	{Gaubert, St\'{e}phane and Grigoriev, Dima and Joswig, Michael and Theobald, Thorsten},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.6.11.168},
  URN =		{urn:nbn:de:0030-drops-71073},
  doi =		{10.4230/DagRep.6.11.168},
  annote =	{Keywords: Algorithms in tropical mathematics, complexity, effective bounds, optimization, zero-sum games}
}
Document
DOI: 10.4230/DagSemRep.323
Integration of Algebra and Geometry Software Systems (Dagstuhl Seminar 01421)

Authors: Michael Joswig and Nobuki Takayama

Published in: Dagstuhl Seminar Reports. Dagstuhl Seminar Reports, Volume 1 (2021)

Abstract
Cite as

Michael Joswig and Nobuki Takayama. Integration of Algebra and Geometry Software Systems (Dagstuhl Seminar 01421). Dagstuhl Seminar Report 323, pp. 1-22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2002)

Copy BibTex To Clipboard

@TechReport{joswig_et_al:DagSemRep.323,
  author =	{Joswig, Michael and Takayama, Nobuki},
  title =	{{Integration of Algebra and Geometry Software Systems (Dagstuhl Seminar 01421)}},
  pages =	{1--22},
  ISSN =	{1619-0203},
  year =	{2002},
  type = 	{Dagstuhl Seminar Report},
  number =	{323},
  institution =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemRep.323},
  URN =		{urn:nbn:de:0030-drops-152070},
  doi =		{10.4230/DagSemRep.323},
}
  • Refine by Type
  • 7 Document/PDF
  • 3 Document/HTML

  • Refine by Publication Year
  • 2 2026
  • 1 2025
  • 1 2020
  • 2 2017
  • 1 2002

  • Refine by Author
  • 3 Joswig, Michael
  • 2 Loho, Georg
  • 1 Disser, Yann
  • 1 Gaubert, Stéphane
  • 1 Grigoriev, Dima
  • Show More...

  • Refine by Series/Journal
  • 4 LIPIcs
  • 1 OASIcs
  • 1 DagRep
  • 1 DagSemRep

  • Refine by Classification
  • 2 Mathematics of computing → Combinatorial algorithms
  • 1 Applied computing → Transportation
  • 1 Mathematics of computing → Algebraic topology
  • 1 Mathematics of computing → Combinatorial optimization
  • 1 Theory of computation → Algorithm design techniques
  • Show More...

  • Refine by Keyword
  • 1 Algorithms in tropical mathematics
  • 1 Computational Topology
  • 1 Discrete Morse Theory
  • 1 Dynamic Programming
  • 1 Exponential Time Hypothesis
  • Show More...

Any Issues?
X

Feedback on the Current Page

CAPTCHA

Thanks for your feedback!

Feedback submitted to Dagstuhl Publishing

Could not send message

Please try again later or send an E-mail
© 2023-2026 Schloss Dagstuhl – LZI GmbH Schloss Dagstuhl – LZI GmbH About DROPS Imprint Privacy Contact