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26th International Conference on Theory and Applications of Satisfiability Testing, SAT 2023

作者： Kirchweger, Markus Peitl, Tomas Szeider, Stefan Algorithms and Complexity Group TU Wien Austria

ISBN: (纸本)9783959772860

In 1972, Paul Erdos, Vance Faber, and Lászlo Lovász asked whether every linear hypergraph with n vertices can be edge-colored with n colors, a statement that has come to be known as the EFL conjecture. Erdos himself considered the conjecture as one of his three favorite open problems, and offered increasing money prizes for its solution on several occasions. A proof of the conjecture was recently announced, for all but a finite number of hypergraphs. In this paper we look at some of the cases not covered by this proof. We use SAT solvers, and in particular the SAT Modulo Symmetries (SMS) framework, to generate non-colorable linear hypergraphs with a fixed number of vertices and hyperedges modulo isomorphisms. Since hypergraph colorability is NP-hard, we cannot directly express in a propositional formula that we want only non-colorable hypergraphs. Instead, we use one SAT (SMS) solver to generate candidate hypergraphs modulo isomorphisms, and another to reject them by finding a coloring. Each successive candidate is required to defeat all previous colorings, whereby we avoid having to generate and test all linear hypergraphs. Computational methods have previously been used to verify the EFL conjecture for small hypergraphs. We verify and extend these results to larger values and discuss challenges and directions. Ours is the first computational approach to the EFL conjecture that allows producing independently verifiable, DRAT proofs. © 2023 Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing. All rights reserved.

关键词： Set theory

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The Parameterized complexity Landscape of the Unsplittable Flow Problem

arXiv

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arXiv 2024年

作者： Ganian, Robert Rocton, Mathis Unterberger, Daniel Algorithms and Complexity Group TU Wien Vienna Austria

We study the well-established problem of finding an optimal routing of unsplittable flows in a graph. While by now there is an extensive body of work targeting the problem on graph classes such as paths and trees, we aim at using the parameterized paradigm to identify its boundaries of tractability on general graphs. We develop novel algorithms and lower bounds which result in a full classification of the parameterized complexity of the problem with respect to natural structural parameterizations for the problem—notably maximum capacity, treewidth, maximum degree, and maximum flow length. In particular, we obtain a fixed-parameter algorithm for the problem when parameterized by all four of these parameters, establish XP-tractability as well as W[1]hardness with respect to the former three and latter three parameters, and all remaining cases remain paraNP-hard. © 2024, CC BY.

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GdMetriX - A NetworkX Extension For Graph Drawing Metrics 32

GdMetriX - A NetworkX Extension For Graph Drawing Metrics

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32nd International Symposium on Graph Drawing and Network Visualization, GD 2024

作者： Nöllenburg, Martin Röder, Sebastian Wallinger, Markus Algorithms and Complexity Group TU Wien Austria TU Wien Austria Chair for Efficient Algorithms Technical University of Munich Germany

ISBN: (纸本)9783959773430

networkX is a well-established Python library for network analysis. With gdMetriX, we aim to extend the functionality of networkX and provide common quality metrics used in the field of graph drawing, such as the number of crossings or the angular resolution. In addition, the package provides easy-to-use access to the graph datasets provided by the 'Graph Layout Benchmark Datasets' project from the Northeastern University Visualization Lab. © Martin Nöllenburg, Sebastian Röder, and Markus Wallinger.

关键词： Data visualization

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The Parameterized complexity of Extending Stack Layouts

arXiv

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arXiv 2024年

作者： Depian, Thomas Fink, Simon D. Ganian, Robert Nöllenburg, Martin Algorithms and Complexity Group TU Wien Vienna Austria

An -page stack layout (also known as an -page book embedding) of a graph is a linear order of the vertex set together with a partition of the edge set into stacks (or pages), such that the endpoints of no two edges on the same stack alternate. We study the problem of extending a given partial -page stack layout into a complete one, which can be seen as a natural generalization of the classical NP-hard problem of computing a stack layout of an input graph from scratch. Given the inherent intractability of the problem, we focus on identifying tractable fragments through the refined lens of parameterized complexity analysis. Our results paint a detailed and surprisingly rich complexitytheoretic landscape of the problem which includes the identification of paraNP-hard, W[1]-hard and XP-tractable, as well as fixed-parameter tractable fragments of stack layout extension via a natural sequence of parameterizations. © 2024, CC BY.

关键词： Graph embeddings

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Block Crossings in One-Sided Tanglegrams 18th

Block Crossings in One-Sided Tanglegrams

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18th International Symposium on algorithms and Data Structures, WADS 2023

作者： Dobler, Alexander Nöllenburg, Martin Algorithms and Complexity Group TU Wien Vienna Austria

ISBN: (纸本)9783031389054

Tanglegrams are drawings of two rooted binary phylogenetic trees and a matching between their leaf sets. The trees are drawn crossing-free on opposite sides with their leaf sets facing each other on two vertical lines. Instead of minimizing the number of pairwise edge crossings, we consider the problem of minimizing the number of block crossings, that is, two bundles of lines crossing each other locally. With one tree fixed, the leaves of the second tree can be permuted according to its tree structure. We give a complete picture of the algorithmic complexity of minimizing block crossings in one-sided tanglegrams by showing NP -completeness, constant-factor approximations, and a fixed-parameter algorithm. We also state first results for non-binary trees. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023.

关键词： Binary trees

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A Structural complexity Analysis of Hierarchical Task Network Planning

arXiv

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arXiv 2024年

作者： Brand, Cornelius Ganian, Robert Inerney, Fion Mc Wietheger, Simon Algorithms & Complexity Theory Group Regensburg University Germany Algorithms and Complexity Group TU Wien Austria Telefónica Scientific Research Barcelona Spain

We perform a refined complexity-theoretic analysis of three classical problems in the context of Hierarchical Task Network Planning: the verification of a provided plan, whether an executable plan exists, and whether a given state can be reached. Our focus lies on identifying structural properties which yield tractability. We obtain new polynomial algorithms for all three problems on a natural class of primitive networks, along with corresponding lower bounds. We also obtain an algorithmic meta-theorem for lifting polynomial-time solvability from primitive to general task networks, and prove that its preconditions are tight. Finally, we analyze the parameterized complexity of the three problems. Copyright © 2024, The Authors. All rights reserved.

关键词： Complex networks

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Self-organized transport in noisy dynamic networks

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Physical Review E 2024年第4期110卷 044310页

作者： Frederic Folz Kurt Mehlhorn Giovanna Morigi Theoretische Physik Algorithms and Complexity Group

We present a numerical study of multicommodity transport in a noisy, nonlinear network. The nonlinearity determines the dynamics of the edge capacities, which can be amplified or suppressed depending on the local current flowing across an edge. We consider network self-organization for three different nonlinear functions: For all three we identify parameter regimes where noise leads to self-organization into more robust topologies, that are not found by the sole noiseless dynamics. Moreover, the interplay between noise and specific functional behavior of the nonlinearity gives rise to different features, such as (i) continuous or discontinuous responses to the demand strength and (ii) either single or multistable solutions. Our study shows the crucial role of the activation function on noise-assisted phenomena.

关键词： Dynamics of networks Biological networks Stochastic dynamical systems Stochastic networks

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CSP Beyond Tractable Constraint Languages 28

CSP Beyond Tractable Constraint Languages

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28th International Conference on Principles and Practice of Constraint Programming, CP 2022

作者： Dreier, Jan Ordyniak, Sebastian Szeider, Stefan Algorithms and Complexity Group TU Wien Austria Algorithms and Complexity Group University of Leeds United Kingdom

ISBN: (纸本)9783959772402

The constraint satisfaction problem (CSP) is among the most studied computational problems. While NP-hard, many tractable subproblems have been identified (Bulatov 2017, Zuk 2017). Backdoors, introduced by Williams, Gomes, and Selman (2003), gradually extend such a tractable class to all CSP instances of bounded distance to the class. Backdoor size provides a natural but rather crude distance measure between a CSP instance and a tractable class. Backdoor depth, introduced by Mählmann, Siebertz, and Vigny (2021) for SAT, is a more refined distance measure, which admits the parallel utilization of different backdoor variables. Bounded backdoor size implies bounded backdoor depth, but there are instances of constant backdoor depth and arbitrarily large backdoor size. Dreier, Ordyniak, and Szeider (2022) provided fixed-parameter algorithms for finding backdoors of small depth into the classes of Horn and Krom formulas. In this paper, we consider backdoor depth for CSP. We consider backdoors w.r.t. tractable subproblems CΓ of the CSP defined by a constraint language Γ, i.e., where all the constraints use relations from the language Γ. Building upon Dreier et al.’s game-theoretic approach and their notion of separator obstructions, we show that for any finite, tractable, semi-conservative constraint language Γ, the CSP is fixed-parameter tractable parameterized by the backdoor depth into CΓ plus the domain size. With backdoors of low depth, we reach classes of instances that require backdoors of arbitrary large size. Hence, our results strictly generalize several known results for CSP that are based on backdoor size. © Jan Dreier, Sebastian Ordyniak, and Stefan Szeider.

关键词： Constraint satisfaction problems

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SAT Backdoors: Depth Beats Size 30

SAT Backdoors: Depth Beats Size

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30th Annual European Symposium on algorithms, ESA 2022

作者： Dreier, Jan Ordyniak, Sebastian Szeider, Stefan Algorithms and Complexity Group TU Wien Austria Algorithms and Complexity Group University of Leeds United Kingdom

ISBN: (纸本)9783959772471

For several decades, much effort has been put into identifying classes of CNF formulas whose satisfiability can be decided in polynomial time. Classic results are the linear-time tractability of Horn formulas (Aspvall, Plass, and Tarjan, 1979) and Krom (i.e., 2CNF) formulas (Dowling and Gallier, 1984). Backdoors, introduced by Williams, Gomes and Selman (2003), gradually extend such a tractable class to all formulas of bounded distance to the class. Backdoor size provides a natural but rather crude distance measure between a formula and a tractable class. Backdoor depth, introduced by Mählmann, Siebertz, and Vigny (2021), is a more refined distance measure, which admits the utilization of different backdoor variables in parallel. Bounded backdoor size implies bounded backdoor depth, but there are formulas of constant backdoor depth and arbitrarily large backdoor size. We propose FPT approximation algorithms to compute backdoor depth into the classes Horn and Krom. This leads to a linear-time algorithm for deciding the satisfiability of formulas of bounded backdoor depth into these classes. We base our FPT approximation algorithm on a sophisticated notion of obstructions, extending Mählmann et al.'s obstruction trees in various ways, including the addition of separator obstructions. We develop the algorithm through a new game-theoretic framework that simplifies the reasoning about backdoors. Finally, we show that bounded backdoor depth captures tractable classes of CNF formulas not captured by any known method. © 2022 Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing. All rights reserved.

关键词： Approximation algorithms

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Boundary Labeling in a Circular Orbit 32

Boundary Labeling in a Circular Orbit

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32nd International Symposium on Graph Drawing and Network Visualization, GD 2024

作者： Bonerath, Annika Nöllenburg, Martin Terziadis, Soeren Wallinger, Markus Wulms, Jules University of Bonn Germany Algorithms and Complexity Group TU Wien Austria TU Eindhoven Netherlands Chair for Efficient Algorithms TU Munich Germany

ISBN: (纸本)9783959773430

Boundary labeling is a well-known method for displaying short textual labels for a set of point features in a figure alongside the boundary of that figure. Labels and their corresponding points are connected via crossing-free leaders. We propose orbital boundary labeling as a new variant of the problem, in which (i) the figure is enclosed by a circular contour and (ii) the labels are placed as disjoint circular arcs in an annulus-shaped orbit around the contour. The algorithmic objective is to compute an orbital boundary labeling with the minimum total leader length. We identify several parameters that define the corresponding problem space: two leader types (straight or orbital-radial), label size and order, presence of candidate label positions, and constraints on where a leader attaches to its label. Our results provide polynomial-time algorithms for many variants and NP-hardness for others, using a variety of geometric and combinatorial insights. © Annika Bonerath, Martin Nöllenburg, Soeren Terziadis, Markus Wallinger, and Jules Wulms.

关键词： Polynomial approximation

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