889 Search Results for "Thomas, Michael"

Document
DOI: 10.4230/LIPIcs.SAT.2026.14
Generalizing CDCL with Graph Backtracking

Authors: Robin Coutelier, Thomas Hader, and Laura Kovács

Published in: LIPIcs, Volume 377, 29th International Conference on Theory and Applications of Satisfiability Testing (SAT 2026)

Abstract
We present graph backtracking, a novel, fine-grained backtracking scheme for CDCL-based SAT solving, parametrized by a user-defined weight function. For conflict repair, we challenge the decision level abstraction and use the implication graph as a precise guiding structure to minimize the weight of literals that are unassigned. Graph backtracking is sound, complete, and terminating. We show that it is a generalization of chronological and non-chronological backtracking by simulating them with specific weight functions. Our approach is implemented in the experimental solver NapSAT. Empirical results show that graph backtracking requires fewer literal propagations than standard approaches, leading to improved solver runtime.
Cite as

Robin Coutelier, Thomas Hader, and Laura Kovács. Generalizing CDCL with Graph Backtracking. In 29th International Conference on Theory and Applications of Satisfiability Testing (SAT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 377, pp. 14:1-14:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{coutelier_et_al:LIPIcs.SAT.2026.14,
  author =	{Coutelier, Robin and Hader, Thomas and Kov\'{a}cs, Laura},
  title =	{{Generalizing CDCL with Graph Backtracking}},
  booktitle =	{29th International Conference on Theory and Applications of Satisfiability Testing (SAT 2026)},
  pages =	{14:1--14:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-431-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{377},
  editor =	{Ignatiev, Alexey and Szeider, Stefan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAT.2026.14},
  URN =		{urn:nbn:de:0030-drops-263203},
  doi =		{10.4230/LIPIcs.SAT.2026.14},
  annote =	{Keywords: SAT Solving, Backtracking, Conflict Analysis, CDCL}
}
Document
Track A: Algorithms, Complexity and Games
DOI: 10.4230/LIPIcs.ICALP.2026.13
Multiplicative Assignment with Upgrades

Authors: Alexander Armbruster, Lars Rohwedder, Stefan Weltge, Andreas Wiese, and Ruilong Zhang

Published in: LIPIcs, Volume 374, 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)

Abstract
We study a problem related to submodular function optimization and the exact matching problem for which we show a rather peculiar status: its natural LP-relaxation can have fractional optimal vertices, but there is always also an optimal integral vertex, which we can also compute in polynomial time. More specifically, we consider the multiplicative assignment problem with upgrades in which we are given a set of customers and suppliers and we seek to assign each customer to a different supplier. Each customer has a demand and each supplier has a regular and an upgraded cost for each unit demand provided to the respective assigned client. Our goal is to upgrade at most k suppliers and to compute an assignment in order to minimize the total resulting cost. This can be cast as the problem to compute an optimal matching in a bipartite graph with the additional constraint that we must select k edges from a certain group of edges, similar to selecting k red edges in the exact matching problem. Also, selecting the suppliers to be upgraded corresponds to maximizing a submodular set function under a cardinality constraint. Our result yields an efficient LP-based algorithm to solve our problem optimally. In addition, we also provide a purely strongly polynomial-time algorithm for it. As an application, we obtain exact algorithms for the upgrading variant of the problem to schedule jobs on identical or uniformly related machines in order to minimize their sum of completion times, i.e., where we may upgrade up to k jobs to reduce their respective processing times.
Cite as

Alexander Armbruster, Lars Rohwedder, Stefan Weltge, Andreas Wiese, and Ruilong Zhang. Multiplicative Assignment with Upgrades. In 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 374, pp. 13:1-13:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{armbruster_et_al:LIPIcs.ICALP.2026.13,
  author =	{Armbruster, Alexander and Rohwedder, Lars and Weltge, Stefan and Wiese, Andreas and Zhang, Ruilong},
  title =	{{Multiplicative Assignment with Upgrades}},
  booktitle =	{53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
  pages =	{13:1--13:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-428-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{374},
  editor =	{Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.13},
  URN =		{urn:nbn:de:0030-drops-264022},
  doi =		{10.4230/LIPIcs.ICALP.2026.13},
  annote =	{Keywords: Scheduling, Bipartite Matching, LP-based Algorithm, Combinatorial Optimization, Resource Allocation}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2026.160
Gray Codes with Constant Delay and Constant Auxiliary Space

Authors: Antoine Amarilli, Claire David, Nadime Francis, Victor Marsault, Mikaël Monet, and Yann Strozecki

Published in: LIPIcs, Volume 374, 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)

Abstract
We give the first two algorithms to enumerate all binary words of {0,1}^𝓁 (like Gray codes) while ensuring that the delay and the auxiliary space is independent from 𝓁, i.e., constant time for each word, and constant memory in addition to the 𝓁 bits storing the current word. Our algorithms are given in two new computational models: tape machines and deque machines. We also study more restricted models, queue machines and stack machines, and show that they cannot enumerate all binary words with constant auxiliary space, even with unrestricted delay. A tape machine is a Turing machine that stores the current binary word on a single working tape of length 𝓁 (which never increases), using no other tape. The machine has a single head and must edit its tape to reach all possible words of {0,1}^𝓁, and output them (in unit time, by entering special output states), with no duplicates. Hence a tape machine uses constant auxiliary space by definition (up to the head position). We construct a tape machine that achieves this task with constant delay between consecutive outputs, so that the machine implements a so-called skew-tolerant quasi-Gray code. We then construct a more involved tape machine that implements a Gray code. A deque machine stores the current binary word on a double-ended queue of length 𝓁, and stores a constant-size internal state. It works as a tape machine, except that it modifies the content of the deque by performing push and pop operations on the endpoints. Hence again a deque machine uses constant auxiliary space by definition. We construct deque machines that enumerate all words of {0,1}^𝓁 with constant-delay. The main technical challenge in this model is to correctly detect when enumeration has finished.
Cite as

Antoine Amarilli, Claire David, Nadime Francis, Victor Marsault, Mikaël Monet, and Yann Strozecki. Gray Codes with Constant Delay and Constant Auxiliary Space. In 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 374, pp. 160:1-160:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{amarilli_et_al:LIPIcs.ICALP.2026.160,
  author =	{Amarilli, Antoine and David, Claire and Francis, Nadime and Marsault, Victor and Monet, Mika\"{e}l and Strozecki, Yann},
  title =	{{Gray Codes with Constant Delay and Constant Auxiliary Space}},
  booktitle =	{53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
  pages =	{160:1--160:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-428-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{374},
  editor =	{Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.160},
  URN =		{urn:nbn:de:0030-drops-265485},
  doi =		{10.4230/LIPIcs.ICALP.2026.160},
  annote =	{Keywords: Gray code, Constant delay, Constant auxiliary space, Enumeration algorithms, Linear bounded automata, Tape machine, Deque machines, Counter implementation}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2026.165
Automata on S-Adic Words

Authors: Valérie Berthé, Toghrul Karimov, and Mihir Vahanwala

Published in: LIPIcs, Volume 374, 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)

Abstract
A fundamental question in logic and verification is the following: for which unary predicates P_1, …, P_k is the monadic second-order theory of ⟨ℕ;<,P_1,…,P_k⟩ decidable? Equivalently, for which infinite words α can we decide whether a given Büchi automaton 𝒜 accepts α? Carton and Thomas showed decidability in the case that α is a fixed point of a letter-to-word substitution σ, i.e., σ(α) = α. However, abundantly more words, e.g., Sturmian words, are characterised by a broader notion of self-similarity that involves a set S of substitutions. A word α is said to be directed by a sequence s = (σ_n)_{n ∈ ℕ} over S if there is a sequence of words (α_n)_{n ∈ ℕ} such that α₀ = α and α_n = σ_n(α_{n+1}) for all n; such α are called S-adic. We study the automaton acceptance problem for such words and prove, among others, the following: given finite S and an automaton 𝒜, we can compute an automaton ℬ that accepts s ∈ S^ω if and only if s directs a word α accepted by 𝒜. Thus we can algorithmically answer questions of the form "Which S-adic words are accepted by a given automaton 𝒜?"
Cite as

Valérie Berthé, Toghrul Karimov, and Mihir Vahanwala. Automata on S-Adic Words. In 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 374, pp. 165:1-165:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{berthe_et_al:LIPIcs.ICALP.2026.165,
  author =	{Berth\'{e}, Val\'{e}rie and Karimov, Toghrul and Vahanwala, Mihir},
  title =	{{Automata on S-Adic Words}},
  booktitle =	{53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
  pages =	{165:1--165:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-428-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{374},
  editor =	{Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.165},
  URN =		{urn:nbn:de:0030-drops-265534},
  doi =		{10.4230/LIPIcs.ICALP.2026.165},
  annote =	{Keywords: Sturmian words, S-adic words, automata theory, word combinatorics}
}
Document
Track A: Algorithms, Complexity and Games
DOI: 10.4230/LIPIcs.ICALP.2026.42
Classification of Local Optimization Problems in Directed Cycles

Authors: Thomas Boudier, Fabian Kuhn, Augusto Modanese, Ronja Stimpert, and Jukka Suomela

Published in: LIPIcs, Volume 374, 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)

Abstract
We present a complete classification of the distributed computational complexity of local optimization problems in directed cycles for both the deterministic and the randomized LOCAL model. We show that for any local optimization problem Π (that can be of the form min-sum, max-sum, min-max, or max-min, for any local cost or utility function over some finite alphabet), and for any constant approximation ratio α, the task of finding an α-approximation of Π in directed cycles has one of the following complexities: 1) O(1) rounds in deterministic LOCAL, O(1) rounds in randomized LOCAL, 2) Θ(log^* n) rounds in deterministic LOCAL, O(1) rounds in randomized LOCAL, 3) Θ(log^* n) rounds in deterministic LOCAL, Θ(log^* n) rounds in randomized LOCAL, 4) Θ(n) rounds in deterministic LOCAL, Θ(n) rounds in randomized LOCAL. Moreover, for any given Π and α, we can determine the complexity class automatically, with an efficient (centralized, sequential) meta-algorithm, and we can also efficiently synthesize an asymptotically optimal distributed algorithm. Before this work, similar results were only known for local search problems (e.g., locally checkable labeling problems). The family of local optimization problems is a strict generalization of local search problems, and it contains numerous commonly studied distributed tasks, such as the problems of finding approximations of the maximum independent set, minimum vertex cover, minimum dominating set, and minimum vertex coloring.
Cite as

Thomas Boudier, Fabian Kuhn, Augusto Modanese, Ronja Stimpert, and Jukka Suomela. Classification of Local Optimization Problems in Directed Cycles. In 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 374, pp. 42:1-42:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{boudier_et_al:LIPIcs.ICALP.2026.42,
  author =	{Boudier, Thomas and Kuhn, Fabian and Modanese, Augusto and Stimpert, Ronja and Suomela, Jukka},
  title =	{{Classification of Local Optimization Problems in Directed Cycles}},
  booktitle =	{53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
  pages =	{42:1--42:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-428-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{374},
  editor =	{Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.42},
  URN =		{urn:nbn:de:0030-drops-264317},
  doi =		{10.4230/LIPIcs.ICALP.2026.42},
  annote =	{Keywords: LOCAL model, optimization, cycles, meta-algorithms}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2026.176
Expregular Functions

Authors: Thomas Colcombet, Nathan Lhote, and Pierre Ohlmann

Published in: LIPIcs, Volume 374, 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)

Abstract
Polyregular functions form a robust class of string-to-string functions with polynomial growth, as evidenced by Bojańczyk (2018). This class admits numerous descriptions and enjoys several closure properties. Most notably, polyregular functions are regularity reflecting (i.e. the inverse image of a regular language is regular). In this work, we propose a robust class of string-to-string functions with exponential growth which we call expregular functions. We consider the following three models for describing them: - MSO set interpretations, which extend MSO interpretations (one of the models capturing polyregular functions), by operating on monadic variables instead of tuples of first-order variables; - yield-Hennie machines, which are branching one-tape Turing machines with bounded visit; and - Ariadne transducers, a new model of 2-way pushdown machines with a bounded visit restriction. Our main contribution is a translation from MSO set interpretations to yield-Hennie machines, which are known to be regularity reflecting (Dartois, Nguy~ên, Peyrat 2026). In particular this establishes that MSO set interpretations are regularity reflecting, which in turn settles a major conjecture about automatic structures: every automatic ω-word has a decidable MSO theory. Yield-Hennie machine directly translate to Ariadne transducers, and our second contribution is to prove that Ariadne transducers also translate to MSO set interpretations, thus establishing the equivalence of the three models. This is obtained by showing that that Ariadne automata - the automaton model corresponding to Ariadne transducers - recognise regular languages.
Cite as

Thomas Colcombet, Nathan Lhote, and Pierre Ohlmann. Expregular Functions. In 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 374, pp. 176:1-176:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{colcombet_et_al:LIPIcs.ICALP.2026.176,
  author =	{Colcombet, Thomas and Lhote, Nathan and Ohlmann, Pierre},
  title =	{{Expregular Functions}},
  booktitle =	{53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
  pages =	{176:1--176:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-428-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{374},
  editor =	{Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.176},
  URN =		{urn:nbn:de:0030-drops-265647},
  doi =		{10.4230/LIPIcs.ICALP.2026.176},
  annote =	{Keywords: monadic second-order logic, exponential growth, automatic structures}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2026.180
Optimally Controlling a Random Population

Authors: Hugo Gimbert, Corto Mascle, and Patrick Totzke

Published in: LIPIcs, Volume 374, 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)

Abstract
The population control problem is a parameterised problem where a controller sends messages to a whole population of identical finite-state agents, aiming to eventually move them all into a target state. The decision problem asks whether this can be achieved for arbitrarily large finite populations. We focus on the randomised version of this problem, where every agent is a copy of the same finite Markov Decision Process and non-determinism in the global action chosen by the controller is resolved independently and uniformly at random. Colcombet, Fijalkow and Ohlmann [Thomas Colcombet et al., 2021] showed that this problem is decidable, but without any complexity upper bound. We show that the random population control problem is in fact ExpTime-complete.
Cite as

Hugo Gimbert, Corto Mascle, and Patrick Totzke. Optimally Controlling a Random Population. In 53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 374, pp. 180:1-180:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{gimbert_et_al:LIPIcs.ICALP.2026.180,
  author =	{Gimbert, Hugo and Mascle, Corto and Totzke, Patrick},
  title =	{{Optimally Controlling a Random Population}},
  booktitle =	{53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
  pages =	{180:1--180:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-428-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{374},
  editor =	{Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.180},
  URN =		{urn:nbn:de:0030-drops-265685},
  doi =		{10.4230/LIPIcs.ICALP.2026.180},
  annote =	{Keywords: Controller synthesis, Parameterized verification}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.2
Different Scales of Randomness: Empirical Mixing Times of the Edge Switching and Curveball MCMC

Authors: Deepak Ajwani, Melvin Kallmayer, Alexander Leonhardt, Ulrich Meyer, Ryan O'Connor, and Manuel Penschuck

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
The Fixed Degree Sequence Model (FDSM) asks for a uniform sample from the set of all simple graphs that match a prescribed degree sequence. It is typically implemented using Markov-Chain Monte-Carlo (MCMC) processes, such as Edge Switching or Curveball (and their variants). Yet despite decades of research, rigorous bounds on the mixing times of such processes remain impractical. Consequently, several experimental techniques have been used to derive "empirical lower bounds" on the mixing time. We address the following research questions: (1) Which commonly studied graph-theoretic properties serve as reliable empirical predictors for mixing of FDSM MCMC processes? (2) At what structural scales do these properties operate primarily (i. e., are they predominantly local or global in nature)? (3) How can these properties be characterised and quantified most effectively? To this end, we propose Claim, a novel systematic method to establish empirical lower bounds using learnt classifiers, and compare it to existing methods. Apart from interesting insights into the usage of machine learning for this problem, we also derive robust graph properties with respect to different randomisation algorithms. Although experimental in nature, these results may influence both theorist’s and algorithm engineer’s work on improved bounds and better algorithm respectively.
Cite as

Deepak Ajwani, Melvin Kallmayer, Alexander Leonhardt, Ulrich Meyer, Ryan O'Connor, and Manuel Penschuck. Different Scales of Randomness: Empirical Mixing Times of the Edge Switching and Curveball MCMC. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 2:1-2:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{ajwani_et_al:LIPIcs.SEA.2026.2,
  author =	{Ajwani, Deepak and Kallmayer, Melvin and Leonhardt, Alexander and Meyer, Ulrich and O'Connor, Ryan and Penschuck, Manuel},
  title =	{{Different Scales of Randomness: Empirical Mixing Times of the Edge Switching and Curveball MCMC}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{2:1--2:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.2},
  URN =		{urn:nbn:de:0030-drops-260062},
  doi =		{10.4230/LIPIcs.SEA.2026.2},
  annote =	{Keywords: Mixing Time, Graph Randomization, Machine Learning, Edge Switching}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.4
Integer Programming Models for the Median of a 0-1 String Set Under Levenshtein Distance

Authors: Claudio Arbib, Andrea D'Ascenzo, Oya E. Karaşan, and Andrea Pizzuti

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
The Median String Problem calls for finding a string that minimizes the average distance from a given set of strings. Under the Levenshtein (or edit) metric, the problem is NP-hard even for binary strings. We devised two novel integer linear programming models for this case and tested them against the only formulation we are aware of in the literature. Our numerical experiments attest to the efficacy of the proposed approach.
Cite as

Claudio Arbib, Andrea D'Ascenzo, Oya E. Karaşan, and Andrea Pizzuti. Integer Programming Models for the Median of a 0-1 String Set Under Levenshtein Distance. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 4:1-4:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{arbib_et_al:LIPIcs.SEA.2026.4,
  author =	{Arbib, Claudio and D'Ascenzo, Andrea and Kara\c{s}an, Oya E. and Pizzuti, Andrea},
  title =	{{Integer Programming Models for the Median of a 0-1 String Set Under Levenshtein Distance}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{4:1--4:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.4},
  URN =		{urn:nbn:de:0030-drops-260081},
  doi =		{10.4230/LIPIcs.SEA.2026.4},
  annote =	{Keywords: Levenshtein Distance, Median String Problem, Integer Programming}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.1
Global Polyline Simplification Under the Fréchet Distance: Theory and Practice

Authors: Christian Abdullahad and Sabine Storandt

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
Given an input polyline with n vertices, the global polyline simplification problem seeks a simplified polyline with the minimum number of vertices whose distance to the original polyline does not exceed a given bound. For the vertex-restricted variant, where the simplified polyline is required to be a subsequence of the input vertices, an algorithm with a running time of 𝒪(n³) was presented in previous work, using the Fréchet distance as the polyline similarity measure. A closely related variant is the local polyline simplification problem, in which the distance bound is required to hold for every individual shortcut segment replacing a sub-polyline. This condition implies that any locally valid simplification is also globally valid, whereas the converse does not hold. As a consequence, globally optimal simplifications may use substantially fewer vertices than locally optimal ones. Indeed, in previous work, instances were constructed in which the optimal global simplification is smaller by a constant factor. On the algorithmic side, optimal local simplifications can be computed significantly faster, namely in 𝒪(n² log n) under the Fréchet distance, and efficient heuristics are also available. This raises the question of which problem variant is more suitable for practical application. In this paper, we first show that there exist instances for which the optimal solution sizes of global and local polyline simplification differ by a factor in Θ(n), substantially strengthening the previously known constant-factor separation. We then present the first practical implementations of existing algorithms for global polyline simplification and experimentally evaluate their performance. To this end, we introduce several engineering techniques that considerably accelerate these algorithms. Moreover, we develop an implicit Fréchet framework that allows many Fréchet-related problems to be addressed in a weaker computational model. Within this framework, explicit geometric computations can be reduced to simple comparisons, resulting in significantly more robust implementations. Somewhat surprisingly, our experimental results reveal that, despite the large worst-case gap established by our theoretical result, the difference in solution size between optimal global and local simplifications is negligible in practice. Motivated by this observation, we propose a heuristic for global polyline simplification that is guaranteed to produce solutions of size equal to or smaller than the optimal local simplification. On a benchmark consisting of one million polylines, the heuristic yields suboptimal results on only eight while being significantly faster than the optimal algorithms.
Cite as

Christian Abdullahad and Sabine Storandt. Global Polyline Simplification Under the Fréchet Distance: Theory and Practice. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 1:1-1:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{abdullahad_et_al:LIPIcs.SEA.2026.1,
  author =	{Abdullahad, Christian and Storandt, Sabine},
  title =	{{Global Polyline Simplification Under the Fr\'{e}chet Distance: Theory and Practice}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{1:1--1:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.1},
  URN =		{urn:nbn:de:0030-drops-260055},
  doi =		{10.4230/LIPIcs.SEA.2026.1},
  annote =	{Keywords: Polyline Simplification, Shortcut Graph, Fr\'{e}chet Distance}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.7
From Relative Compression to Hierarchical Compression

Authors: Philip Bille, Inge Li Gørtz, and Máximo Pérez-López

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
We introduce a framework to use any relative compression algorithm as a subroutine for hierarchical relative compression. In a dataset consisting of n sequences, it consists of constructing a rooted tree on the sequences, using hashing and similarity techniques, and compressing the children of a node relative to their parent. We build up on previous techniques [Bille et al., 2023], and optimize them further for computational efficiency. We test our framework with three existing relative compression algorithms on six genomic datasets, and we show that in datasets that contain heterogeneous data, hierarchical relative compression improves the compression ratio by a factor 2 or more, when compared to relative compression to a single sequence. Apart from compression ratio, we also explore the trade-offs with respect to compression speed, dataset decompression speed, and average sequence decompression speed. With two of the surveyed algorithms, dataset decompression becomes faster and sequence decompression remains practical, at the cost of compression time, which remains competitive for the datasets with highest variability.
Cite as

Philip Bille, Inge Li Gørtz, and Máximo Pérez-López. From Relative Compression to Hierarchical Compression. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 7:1-7:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{bille_et_al:LIPIcs.SEA.2026.7,
  author =	{Bille, Philip and G{\o}rtz, Inge Li and P\'{e}rez-L\'{o}pez, M\'{a}ximo},
  title =	{{From Relative Compression to Hierarchical Compression}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{7:1--7:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.7},
  URN =		{urn:nbn:de:0030-drops-260117},
  doi =		{10.4230/LIPIcs.SEA.2026.7},
  annote =	{Keywords: Relative compression, RLZ, string collections, compressed representation, data structures, efficient algorithms}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.12
Fast Select Queries Using Hybrid Bitvectors

Authors: Eric Chiu and Dominik Kempa

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
One of the central problems in the design of compressed data structures is the efficient support for rank and select queries on bitvectors. These two operations form the backbone of more complex data structures used for the compact representation of texts, trees, graphs, or grids. One effective solution is the so-called hybrid bitvector implementation, which partitions the input bitvector into blocks and adaptively selects an encoding method - such as run-length, plain, or minority encoding - based on local redundancy. Experiments have shown that hybrid bitvectors achieve excellent all-around performance on repetitive and non-repetitive inputs. Current hybrid bitvector implementations, however, support only rank queries (i.e., counting the number of ones up to a given position) and lack support for select queries (which ask for the position of a given occurrence of a given bit), which limits their applicability. In this paper, we propose a method to add support for select queries to hybrid bitvectors, and we evaluate the resulting implementation on repetitive and non-repetitive inputs. Our results show that hybrid bitvectors offer very strong all-around performance, combining high query speed with space efficiency and remaining consistently on or near the Pareto frontier.
Cite as

Eric Chiu and Dominik Kempa. Fast Select Queries Using Hybrid Bitvectors. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 12:1-12:11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{chiu_et_al:LIPIcs.SEA.2026.12,
  author =	{Chiu, Eric and Kempa, Dominik},
  title =	{{Fast Select Queries Using Hybrid Bitvectors}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{12:1--12:11},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.12},
  URN =		{urn:nbn:de:0030-drops-260168},
  doi =		{10.4230/LIPIcs.SEA.2026.12},
  annote =	{Keywords: compressed bitvectors, hybrid bitvector, select queries}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.24
ZOR Filters: Fast and Smaller Than Fuse Filters

Authors: Antoine Limasset

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
Probabilistic membership filters support fast approximate membership queries with controlled false-positive probability ε and are widely used across storage, analytics, networking, and bioinformatics [Chang et al., 2008; Niv Dayan et al., 2018; Broder and Mitzenmacher, 2004; Harris and Medvedev, 2020; Marchet and Limasset, 2023; Chikhi et al., 2025; Hernandez-Courbevoie et al., 2025]. In the static setting, low-overhead methods such as XOR, Fuse, and BuRR have been proposed [Graf and Lemire, 2020; Graf and Lemire, 2022; Dillinger et al., 2022; Ulrich and Renard, 2023]. Among these, Fuse filters are known for near-optimal query throughput. For XOR/Fuse-style peeling constructions, however, build success is only high probability, which complicates deterministic builds. We introduce ZOR filters, a deterministic continuation of XOR/Fuse-style constructions that guarantees termination while preserving the same XOR-based query mechanism. ZOR replaces restart-on-failure with deterministic peeling that abandons a small fraction of keys, and restores false-positive-only semantics by storing the remainder in a compact auxiliary structure. In our experiments, the abandoned fraction drops below 1% for moderate arity (e.g., N ≥ 5), so the auxiliary handles a negligible fraction of keys. As a result, ZOR filters can be substantially more memory-efficient than Fuse filters, with overhead below 1%, while not yet matching the near-optimal overhead of BuRR (below 0.1%). In query performance, ZOR-pure is close to Fuse and faster than BuRR on positive queries, while the complete interleaved variant trades additional negative-query latency for deterministic continuation. Relative to optimised Fuse/BuRR implementations [Graf and Lemire, 2022; Dillinger et al., 2022], the current ZOR prototype remains slower in construction because deterministic peeling requires explicit incidence handling; reducing this construction gap is an important direction for future work.
Cite as

Antoine Limasset. ZOR Filters: Fast and Smaller Than Fuse Filters. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 24:1-24:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{limasset:LIPIcs.SEA.2026.24,
  author =	{Limasset, Antoine},
  title =	{{ZOR Filters: Fast and Smaller Than Fuse Filters}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{24:1--24:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.24},
  URN =		{urn:nbn:de:0030-drops-260281},
  doi =		{10.4230/LIPIcs.SEA.2026.24},
  annote =	{Keywords: Data structure, Approximate Set Membership, Static filter}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.25
Engineering Learned Heuristics to Improve Clustering for Multilevel Graph Partitioning

Authors: Simeon Schrape, Nikolai Maas, Kenneth Langedal, and Daniel Seemaier

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
Balanced Graph Partitioning is a classical optimization problem where quality guarantees are computationally infeasible, and practical solvers therefore rely on manually engineered heuristics. Yet, the problem has also proven difficult for approaches that rely heavily on machine learning - especially since applications often need to partition graphs of huge scale in a short amount of time. Instead, we demonstrate how to achieve practical improvements with a more careful approach that uses machine learning to improve heuristic decisions within the state-of-the-art solver Mt-KaHyPar. We use a pre-trained neural network to predict a score for each edge, which then guides clustering decisions in the first phase of the partitioning (the coarsening). Combined with corresponding adjustments to the clustering algorithm and an efficient implementation of the neural network logic, we improve the overall solution quality while preserving the efficiency and scalability of the original algorithm. Our detailed evaluation on more than 180 graphs shows an average quality improvement of 2% on a class of graphs with beneficial properties, and unchanged quality on all remaining graphs. Moreover, our improvements generalize to a set of instances from the literature that are much larger than the graphs used during training.
Cite as

Simeon Schrape, Nikolai Maas, Kenneth Langedal, and Daniel Seemaier. Engineering Learned Heuristics to Improve Clustering for Multilevel Graph Partitioning. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 25:1-25:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{schrape_et_al:LIPIcs.SEA.2026.25,
  author =	{Schrape, Simeon and Maas, Nikolai and Langedal, Kenneth and Seemaier, Daniel},
  title =	{{Engineering Learned Heuristics to Improve Clustering for Multilevel Graph Partitioning}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{25:1--25:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.25},
  URN =		{urn:nbn:de:0030-drops-260295},
  doi =		{10.4230/LIPIcs.SEA.2026.25},
  annote =	{Keywords: Graph Partitioning, Graph Algorithms, Machine Learning, Neural Networks}
}
Document
DOI: 10.4230/LIPIcs.SEA.2026.26
Engineering Algorithms for Dynamic Greedy Set Cover

Authors: Amitai Uzrad

Published in: LIPIcs, Volume 371, 24th International Symposium on Experimental Algorithms (SEA 2026)

Abstract
In the dynamic set cover problem, the input is a dynamic universe of elements and a fixed collection of sets. As elements are inserted or deleted, the goal is to efficiently maintain an approximate minimum set cover. While the past decade has seen significant theoretical breakthroughs for this problem, a notable gap remains between theoretical design and practical performance, as no comprehensive experimental study currently exists to validate these results. In this paper, we bridge this gap by implementing and evaluating four greedy-based dynamic algorithms across a diverse range of real-world instances. We derive our implementations from state-of-the-art frameworks - such as [GKKP(STOC'17); SU(STOC'23); SUZ(FOCS'24)] - which we simplify by identifying and modifying intricate subroutines that optimize asymptotic bounds but hinder practical performance. We evaluate these algorithms based on solution quality (set cover size) and efficiency, which comprises update time - the time required to update the solution following each insertion/deletion - and recourse - the number of changes made to the solution per update. Each algorithm uses a parameter β to balance quality against efficiency; we investigate the influence of this tradeoff parameter on each algorithm and then perform a comparative analysis to evaluate the algorithms against each other. Our results provide the first practical insights into which algorithmic strategies provide the most value in realistic scenarios.
Cite as

Amitai Uzrad. Engineering Algorithms for Dynamic Greedy Set Cover. In 24th International Symposium on Experimental Algorithms (SEA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 371, pp. 26:1-26:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{uzrad:LIPIcs.SEA.2026.26,
  author =	{Uzrad, Amitai},
  title =	{{Engineering Algorithms for Dynamic Greedy Set Cover}},
  booktitle =	{24th International Symposium on Experimental Algorithms (SEA 2026)},
  pages =	{26:1--26:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-422-2},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{371},
  editor =	{Aum\"{u}ller, Martin and Finocchi, Irene},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2026.26},
  URN =		{urn:nbn:de:0030-drops-260308},
  doi =		{10.4230/LIPIcs.SEA.2026.26},
  annote =	{Keywords: Dynamic graphs, set cover, recourse}
}
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