67 Search Results for "L�th, Christoph"

Document
DOI: 10.4230/LIPIcs.CONCUR.2023.13
Universal Quantification Makes Automatic Structures Hard to Decide

Authors: Christoph Haase and Radosław Piórkowski

Published in: LIPIcs, Volume 279, 34th International Conference on Concurrency Theory (CONCUR 2023)

Abstract
Automatic structures are structures whose universe and relations can be represented as regular languages. It follows from the standard closure properties of regular languages that the first-order theory of an automatic structure is decidable. While existential quantifiers can be eliminated in linear time by application of a homomorphism, universal quantifiers are commonly eliminated via the identity ∀x.Φ≡¬(∃x.¬Φ). If Φ is represented in the standard way as an NFA, a priori this approach results in a doubly exponential blow-up. However, the recent literature has shown that there are classes of automatic structures for which universal quantifiers can be eliminated by different means without this blow-up by treating them as first-class citizens and not resorting to double complementation. While existing lower bounds for some classes of automatic structures show that a singly exponential blow-up is unavoidable when eliminating a universal quantifier, it is not known whether there may be better approaches that avoid the naïve doubly exponential blow-up, perhaps at least in restricted settings. In this paper, we answer this question negatively and show that there is a family of NFA representing automatic relations for which the minimal NFA recognising the language after eliminating a single universal quantifier is doubly exponential, and deciding whether this language is empty is ExpSpace-complete.
Cite as

Christoph Haase and Radosław Piórkowski. Universal Quantification Makes Automatic Structures Hard to Decide. In 34th International Conference on Concurrency Theory (CONCUR 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 279, pp. 13:1-13:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{haase_et_al:LIPIcs.CONCUR.2023.13,
  author =	{Haase, Christoph and Pi\'{o}rkowski, Rados{\l}aw},
  title =	{{Universal Quantification Makes Automatic Structures Hard to Decide}},
  booktitle =	{34th International Conference on Concurrency Theory (CONCUR 2023)},
  pages =	{13:1--13:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-299-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{279},
  editor =	{P\'{e}rez, Guillermo A. and Raskin, Jean-Fran\c{c}ois},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2023.13},
  URN =		{urn:nbn:de:0030-drops-190075},
  doi =		{10.4230/LIPIcs.CONCUR.2023.13},
  annote =	{Keywords: automatic structures, universal projection, state complexity, tiling problems}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2022.23
Regular Model Checking Upside-Down: An Invariant-Based Approach

Authors: Javier Esparza, Mikhail Raskin, and Christoph Welzel

Published in: LIPIcs, Volume 243, 33rd International Conference on Concurrency Theory (CONCUR 2022)

Abstract
Regular model checking is a technique for the verification of infinite-state systems whose configurations can be represented as finite words over a suitable alphabet. It applies to systems whose set of initial configurations is regular, and whose transition relation is captured by a length-preserving transducer. To verify safety properties, regular model checking iteratively computes automata recognizing increasingly larger regular sets of reachable configurations, and checks if they contain unsafe configurations. Since this procedure often does not terminate, acceleration, abstraction, and widening techniques have been developed to compute a regular superset of the reachable configurations. In this paper we develop a complementary procedure. Instead of approaching the set of reachable configurations from below, we start with the set of all configurations and approach it from above. We use that the set of reachable configurations is equal to the intersection of all inductive invariants of the system. Since this intersection is non-regular in general, we introduce b-bounded invariants, defined as those representable by CNF-formulas with at most b clauses. We prove that, for every b ≥ 0, the intersection of all b-bounded inductive invariants is regular, and we construct an automaton recognizing it. We show that whether this automaton accepts some unsafe configuration is in EXPSPACE for every b ≥ 0, and PSPACE-complete for b = 1. Finally, we study how large must b be to prove safety properties of a number of benchmarks.
Cite as

Javier Esparza, Mikhail Raskin, and Christoph Welzel. Regular Model Checking Upside-Down: An Invariant-Based Approach. In 33rd International Conference on Concurrency Theory (CONCUR 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 243, pp. 23:1-23:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{esparza_et_al:LIPIcs.CONCUR.2022.23,
  author =	{Esparza, Javier and Raskin, Mikhail and Welzel, Christoph},
  title =	{{Regular Model Checking Upside-Down: An Invariant-Based Approach}},
  booktitle =	{33rd International Conference on Concurrency Theory (CONCUR 2022)},
  pages =	{23:1--23:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-246-4},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{243},
  editor =	{Klin, Bartek and Lasota, S{\l}awomir and Muscholl, Anca},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2022.23},
  URN =		{urn:nbn:de:0030-drops-170862},
  doi =		{10.4230/LIPIcs.CONCUR.2022.23},
  annote =	{Keywords: parameterized verification, structural analysis, regular languages, regular model-checking, traps}
}
Document
DOI: 10.4230/LIPIcs.ITCS.2022.32
Small Hazard-Free Transducers

Authors: Johannes Bund, Christoph Lenzen, and Moti Medina

Published in: LIPIcs, Volume 215, 13th Innovations in Theoretical Computer Science Conference (ITCS 2022)

Abstract
Ikenmeyer et al. (JACM'19) proved an unconditional exponential separation between the hazard-free complexity and (standard) circuit complexity of explicit functions. This raises the question: which classes of functions permit efficient hazard-free circuits? In this work, we prove that circuit implementations of transducers with small state space are such a class. A transducer is a finite state machine that transcribes, symbol by symbol, an input string of length n into an output string of length n. We present a construction that transforms any function arising from a transducer into an efficient circuit of size 𝒪(n) computing the hazard-free extension of the function. More precisely, given a transducer with s states, receiving n input symbols encoded by l bits, and computing n output symbols encoded by m bits, the transducer has a hazard-free circuit of size n*m*2^{𝒪(s+𝓁)} and depth 𝒪(s*log(n) + 𝓁); in particular, if s, 𝓁,m ∈ 𝒪(1), size and depth are asymptotically optimal. In light of the strong hardness results by Ikenmeyer et al. (JACM'19), we consider this a surprising result.
Cite as

Johannes Bund, Christoph Lenzen, and Moti Medina. Small Hazard-Free Transducers. In 13th Innovations in Theoretical Computer Science Conference (ITCS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 215, pp. 32:1-32:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bund_et_al:LIPIcs.ITCS.2022.32,
  author =	{Bund, Johannes and Lenzen, Christoph and Medina, Moti},
  title =	{{Small Hazard-Free Transducers}},
  booktitle =	{13th Innovations in Theoretical Computer Science Conference (ITCS 2022)},
  pages =	{32:1--32:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-217-4},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{215},
  editor =	{Braverman, Mark},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2022.32},
  URN =		{urn:nbn:de:0030-drops-156281},
  doi =		{10.4230/LIPIcs.ITCS.2022.32},
  annote =	{Keywords: Hazard-Freeness, Parallel Prefix Computation, Finite State Transducers}
}
Document
DOI: 10.4230/LIPIcs.ISAAC.2021.21
Partitioning H-Free Graphs of Bounded Diameter

Authors: Christoph Brause, Petr Golovach, Barnaby Martin, Daniël Paulusma, and Siani Smith

Published in: LIPIcs, Volume 212, 32nd International Symposium on Algorithms and Computation (ISAAC 2021)

Abstract
A natural way of increasing our understanding of NP-complete graph problems is to restrict the input to a special graph class. Classes of H-free graphs, that is, graphs that do not contain some graph H as an induced subgraph, have proven to be an ideal testbed for such a complexity study. However, if the forbidden graph H contains a cycle or claw, then these problems often stay NP-complete. A recent complexity study (MFCS 2019) on the k-Colouring problem shows that we may still obtain tractable results if we also bound the diameter of the H-free input graph. We continue this line of research by initiating a complexity study on the impact of bounding the diameter for a variety of classical vertex partitioning problems restricted to H-free graphs. We prove that bounding the diameter does not help for Independent Set, but leads to new tractable cases for problems closely related to 3-Colouring. That is, we show that Near-Bipartiteness, Independent Feedback Vertex Set, Independent Odd Cycle Transversal, Acyclic 3-Colouring and Star 3-Colouring are all polynomial-time solvable for chair-free graphs of bounded diameter. To obtain these results we exploit a new structural property of 3-colourable chair-free graphs.
Cite as

Christoph Brause, Petr Golovach, Barnaby Martin, Daniël Paulusma, and Siani Smith. Partitioning H-Free Graphs of Bounded Diameter. In 32nd International Symposium on Algorithms and Computation (ISAAC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 212, pp. 21:1-21:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{brause_et_al:LIPIcs.ISAAC.2021.21,
  author =	{Brause, Christoph and Golovach, Petr and Martin, Barnaby and Paulusma, Dani\"{e}l and Smith, Siani},
  title =	{{Partitioning H-Free Graphs of Bounded Diameter}},
  booktitle =	{32nd International Symposium on Algorithms and Computation (ISAAC 2021)},
  pages =	{21:1--21:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-214-3},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{212},
  editor =	{Ahn, Hee-Kap and Sadakane, Kunihiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2021.21},
  URN =		{urn:nbn:de:0030-drops-154543},
  doi =		{10.4230/LIPIcs.ISAAC.2021.21},
  annote =	{Keywords: vertex partitioning problem, H-free, diameter, complexity dichotomy}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.ICDT.2020.3
Current Challenges in Graph Databases (Invited Talk)

Authors: Juan L. Reutter

Published in: LIPIcs, Volume 155, 23rd International Conference on Database Theory (ICDT 2020)

Abstract
As graph databases grow in popularity, decades of work in graph query languages and models are materialising in industry standards and in the construction of new graph database systems. However, this surge in graph systems has in turn opened up a series of new, interesting research problems related to graph databases. Our first set of problems has to do with more efficient ways of computing the answers of graph queries, specifically graph patterns, path queries, and combinations between them. Traditionally, researchers in graph databases have pointed out that relational systems are ill-equipped to process these types of queries, and if one looks at the performance of native graph database systems, there is clearly a lot of room for improvement. The talk focuses on two possible directions for improving the state of the art in graph query processing. The first is implementing worst-case optimal algorithms for processing graph patterns that traduce in relational queries with several joins. Some advances are already in development (see e.g. Nguyen, Dung, et al. "Join processing for graph patterns: An old dog with new tricks." GRADES'15. or Hogan, Aidan, et al. "A Worst-Case Optimal Join Algorithm for SPARQL." ISWC’19.), but we are still far from a full fledged solution: most algorithms require complex data structures, or need further support in terms of heuristics to select an order in which joins are processed. Second, we need to understand what is the best way of evaluating path queries (that is, finding all pairs of nodes connected by a path), in such a way that these results can be further integrated with other query results in a graph system pipeline. We already have complexity results regarding path computation and enumeration for different semantics of path queries (see e.g. Martens, Wim, and Tina Trautner. "Evaluation and enumeration problems for regular path queries." ICDT'18. or Bagan, Guillaume, Angela Bonifati, and Benoit Groz. "A trichotomy for regular simple path queries on graphs." PODS'13.), but still very little is known in terms of optimal processing of path queries when inside a tractable fragment. Our second set of problems is related to graph analytics, one of the current selling points of graph databases. Systems should be able to run more complex analytical queries involving tasks such as more complex path finding, centrality or clustering. It is also important to be able to run these algorithms not over native graphs, but perhaps over a certain set of nodes or edges previously selected by a graph query, and one may also want to pose further queries over the result of the analytics task. Finally, all of this should be done in an efficient way, specially in the prospect that graph databases may contain a huge amount of nodes. In this talk I will discuss possible approaches to perform these operations, covering aspects from the design of languages for graph analytics to efficient ways of processing them, and also comparing the expressive power of graph analytics solutions with other forms of graph computation.
Cite as

Juan L. Reutter. Current Challenges in Graph Databases (Invited Talk). In 23rd International Conference on Database Theory (ICDT 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 155, p. 3:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{reutter:LIPIcs.ICDT.2020.3,
  author =	{Reutter, Juan L.},
  title =	{{Current Challenges in Graph Databases}},
  booktitle =	{23rd International Conference on Database Theory (ICDT 2020)},
  pages =	{3:1--3:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-139-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{155},
  editor =	{Lutz, Carsten and Jung, Jean Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2020.3},
  URN =		{urn:nbn:de:0030-drops-119272},
  doi =		{10.4230/LIPIcs.ICDT.2020.3},
  annote =	{Keywords: Graph databases, Join algorithms, path queries, graph analytics}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2020.21
Optimal Joins Using Compact Data Structures

Authors: Gonzalo Navarro, Juan L. Reutter, and Javiel Rojas-Ledesma

Published in: LIPIcs, Volume 155, 23rd International Conference on Database Theory (ICDT 2020)

Abstract
Worst-case optimal join algorithms have gained a lot of attention in the database literature. We now count with several algorithms that are optimal in the worst case, and many of them have been implemented and validated in practice. However, the implementation of these algorithms often requires an enhanced indexing structure: to achieve optimality we either need to build completely new indexes, or we must populate the database with several instantiations of indexes such as B+-trees. Either way, this means spending an extra amount of storage space that may be non-negligible. We show that optimal algorithms can be obtained directly from a representation that regards the relations as point sets in variable-dimensional grids, without the need of extra storage. Our representation is a compact quadtree for the static indexes, and a dynamic quadtree sharing subtrees (which we dub a qdag) for intermediate results. We develop a compositional algorithm to process full join queries under this representation, and show that the running time of this algorithm is worst-case optimal in data complexity. Remarkably, we can extend our framework to evaluate more expressive queries from relational algebra by introducing a lazy version of qdags (lqdags). Once again, we can show that the running time of our algorithms is worst-case optimal.
Cite as

Gonzalo Navarro, Juan L. Reutter, and Javiel Rojas-Ledesma. Optimal Joins Using Compact Data Structures. In 23rd International Conference on Database Theory (ICDT 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 155, pp. 21:1-21:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{navarro_et_al:LIPIcs.ICDT.2020.21,
  author =	{Navarro, Gonzalo and Reutter, Juan L. and Rojas-Ledesma, Javiel},
  title =	{{Optimal Joins Using Compact Data Structures}},
  booktitle =	{23rd International Conference on Database Theory (ICDT 2020)},
  pages =	{21:1--21:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-139-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{155},
  editor =	{Lutz, Carsten and Jung, Jean Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2020.21},
  URN =		{urn:nbn:de:0030-drops-119453},
  doi =		{10.4230/LIPIcs.ICDT.2020.21},
  annote =	{Keywords: Join algorithms, Compact data structures, Quadtrees, AGM bound}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2020.24
Reverse Prevention Sampling for Misinformation Mitigation in Social Networks

Authors: Michael Simpson, Venkatesh Srinivasan, and Alex Thomo

Published in: LIPIcs, Volume 155, 23rd International Conference on Database Theory (ICDT 2020)

Abstract
In this work, we consider misinformation propagating through a social network and study the problem of its prevention. In this problem, a "bad" campaign starts propagating from a set of seed nodes in the network and we use the notion of a limiting (or "good") campaign to counteract the effect of misinformation. The goal is to identify a set of k users that need to be convinced to adopt the limiting campaign so as to minimize the number of people that adopt the "bad" campaign at the end of both propagation processes. This work presents RPS (Reverse Prevention Sampling), an algorithm that provides a scalable solution to the misinformation prevention problem. Our theoretical analysis shows that RPS runs in O((k + l)(n + m)(1/(1 - γ)) log n / ε²) expected time and returns a (1 - 1/e - ε)-approximate solution with at least 1 - n^{-l} probability (where γ is a typically small network parameter and l is a confidence parameter). The time complexity of RPS substantially improves upon the previously best-known algorithms that run in time Ω(m n k ⋅ POLY(ε^{-1})). We experimentally evaluate RPS on large datasets and show that it outperforms the state-of-the-art solution by several orders of magnitude in terms of running time. This demonstrates that misinformation prevention can be made practical while still offering strong theoretical guarantees.
Cite as

Michael Simpson, Venkatesh Srinivasan, and Alex Thomo. Reverse Prevention Sampling for Misinformation Mitigation in Social Networks. In 23rd International Conference on Database Theory (ICDT 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 155, pp. 24:1-24:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{simpson_et_al:LIPIcs.ICDT.2020.24,
  author =	{Simpson, Michael and Srinivasan, Venkatesh and Thomo, Alex},
  title =	{{Reverse Prevention Sampling for Misinformation Mitigation in Social Networks}},
  booktitle =	{23rd International Conference on Database Theory (ICDT 2020)},
  pages =	{24:1--24:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-139-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{155},
  editor =	{Lutz, Carsten and Jung, Jean Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2020.24},
  URN =		{urn:nbn:de:0030-drops-119484},
  doi =		{10.4230/LIPIcs.ICDT.2020.24},
  annote =	{Keywords: Graph Algorithms, Social Networks, Misinformation Prevention}
}
Document
Short Paper
DOI: 10.4230/LIPIcs.COSIT.2019.3
Functional Scales in Assisted Wayfinding (Short Paper)

Authors: Heinrich Löwen, Jakub Krukar, and Angela Schwering

Published in: LIPIcs, Volume 142, 14th International Conference on Spatial Information Theory (COSIT 2019)

Abstract
GPS-based navigation systems are widely used to get wayfinding assistance. Current navigation systems incorporate different map scales for presenting wayfinding instructions, however, the selection of scale is not supported by psychological findings. Different tasks of the users such as the identification of the next decision point or the orientation within the environment might be supported best at particular scales. We propose a new conceptual distinction of functional scales with respect to their role in supporting wayfinding and orientation. We suggest that these functional scales can have a benefit for supporting wayfinding and orientation if used for providing wayfinding instructions. This we aim to empirically evaluate in future work.
Cite as

Heinrich Löwen, Jakub Krukar, and Angela Schwering. Functional Scales in Assisted Wayfinding (Short Paper). In 14th International Conference on Spatial Information Theory (COSIT 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 142, pp. 3:1-3:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{lowen_et_al:LIPIcs.COSIT.2019.3,
  author =	{L\"{o}wen, Heinrich and Krukar, Jakub and Schwering, Angela},
  title =	{{Functional Scales in Assisted Wayfinding}},
  booktitle =	{14th International Conference on Spatial Information Theory (COSIT 2019)},
  pages =	{3:1--3:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-115-3},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{142},
  editor =	{Timpf, Sabine and Schlieder, Christoph and Kattenbeck, Markus and Ludwig, Bernd and Stewart, Kathleen},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.COSIT.2019.3},
  URN =		{urn:nbn:de:0030-drops-110953},
  doi =		{10.4230/LIPIcs.COSIT.2019.3},
  annote =	{Keywords: navigation, wayfinding support, orientation information, scale}
}
Document
DOI: 10.4230/LIPIcs.COSIT.2019.22
Planning and Explanations with a Learned Spatial Model

Authors: Susan L. Epstein and Raj Korpan

Published in: LIPIcs, Volume 142, 14th International Conference on Spatial Information Theory (COSIT 2019)

Abstract
This paper reports on a robot controller that learns and applies a cognitively-based spatial model as it travels in challenging, real-world indoor spaces. The model not only describes indoor space, but also supports robust, model-based planning. Together with the spatial model, the controller’s reasoning framework allows it to explain and defend its decisions in accessible natural language. The novel contributions of this paper are an enhanced cognitive spatial model that facilitates successful reasoning and planning, and the ability to explain navigation choices for a complex environment. Empirical evidence is provided by simulation of a commercial robot in a large, complex, realistic world.
Cite as

Susan L. Epstein and Raj Korpan. Planning and Explanations with a Learned Spatial Model. In 14th International Conference on Spatial Information Theory (COSIT 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 142, pp. 22:1-22:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{epstein_et_al:LIPIcs.COSIT.2019.22,
  author =	{Epstein, Susan L. and Korpan, Raj},
  title =	{{Planning and Explanations with a Learned Spatial Model}},
  booktitle =	{14th International Conference on Spatial Information Theory (COSIT 2019)},
  pages =	{22:1--22:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-115-3},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{142},
  editor =	{Timpf, Sabine and Schlieder, Christoph and Kattenbeck, Markus and Ludwig, Bernd and Stewart, Kathleen},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.COSIT.2019.22},
  URN =		{urn:nbn:de:0030-drops-111148},
  doi =		{10.4230/LIPIcs.COSIT.2019.22},
  annote =	{Keywords: navigation, planning, learning, explanation, spatial model, heuristics}
}
Document
DOI: 10.4230/OASIcs.WCET.2018.9
Fine-Grain Iterative Compilation for WCET Estimation

Authors: Isabelle Puaut, Mickaël Dardaillon, Christoph Cullmann, Gernot Gebhard, and Steven Derrien

Published in: OASIcs, Volume 63, 18th International Workshop on Worst-Case Execution Time Analysis (WCET 2018)

Abstract
Compiler optimizations, although reducing the execution times of programs, raise issues in static WCET estimation techniques and tools. Flow facts, such as loop bounds, may not be automatically found by static WCET analysis tools after aggressive code optimizations. In this paper, we explore the use of iterative compilation (WCET-directed program optimization to explore the optimization space), with the objective to (i) allow flow facts to be automatically found and (ii) select optimizations that result in the lowest WCET estimates. We also explore to which extent code outlining helps, by allowing the selection of different optimization options for different code snippets of the application.
Cite as

Isabelle Puaut, Mickaël Dardaillon, Christoph Cullmann, Gernot Gebhard, and Steven Derrien. Fine-Grain Iterative Compilation for WCET Estimation. In 18th International Workshop on Worst-Case Execution Time Analysis (WCET 2018). Open Access Series in Informatics (OASIcs), Volume 63, pp. 9:1-9:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{puaut_et_al:OASIcs.WCET.2018.9,
  author =	{Puaut, Isabelle and Dardaillon, Micka\"{e}l and Cullmann, Christoph and Gebhard, Gernot and Derrien, Steven},
  title =	{{Fine-Grain Iterative Compilation for WCET Estimation}},
  booktitle =	{18th International Workshop on Worst-Case Execution Time Analysis (WCET 2018)},
  pages =	{9:1--9:12},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-073-6},
  ISSN =	{2190-6807},
  year =	{2018},
  volume =	{63},
  editor =	{Brandner, Florian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2018.9},
  URN =		{urn:nbn:de:0030-drops-97556},
  doi =		{10.4230/OASIcs.WCET.2018.9},
  annote =	{Keywords: Worst-Case Execution Time Estimation, Compiler optimizations, Iterative Compilation, Flow fact extraction, Outlining}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2018.8
Online Maximum Matching with Recourse

Authors: Spyros Angelopoulos, Christoph Dürr, and Shendan Jin

Published in: LIPIcs, Volume 117, 43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018)

Abstract
We study the online maximum matching problem in a model in which the edges are associated with a known recourse parameter k. An online algorithm for this problem has to maintain a valid matching while edges of the underlying graph are presented one after the other. At any moment the algorithm can decide to include an edge into the matching or to exclude it, under the restriction that at most k such actions per edge take place, where k is typically a small constant. This problem was introduced and studied in the context of general online packing problems with recourse by Avitabile et al. [Avitabile et al., 2013], whereas the special case k=2 was studied by Boyar et al. [Boyar et al., 2017]. In the first part of this paper, we consider the edge arrival model, in which an arriving edge never disappears from the graph. Here, we first show an improved analysis on the performance of the algorithm AMP given in [Avitabile et al., 2013], by exploiting the structure of the matching problem. In addition, we extend the result of [Boyar et al., 2017] and show that the greedy algorithm has competitive ratio 3/2 for every even k and ratio 2 for every odd k. Moreover, we present and analyze an improvement of the greedy algorithm which we call L-Greedy, and we show that for small values of k it outperforms the algorithm of [Avitabile et al., 2013]. In terms of lower bounds, we show that no deterministic algorithm better than 1+1/(k-1) exists, improving upon the lower bound of 1+1/k shown in [Avitabile et al., 2013]. The second part of the paper is devoted to the edge arrival/departure model, which is the fully dynamic variant of online matching with recourse. The analysis of L-Greedy and AMP carry through in this model; moreover we show a lower bound of (k^2-3k+6)/(k^2-4k+7) for all even k >= 4. For k in {2,3}, the competitive ratio is 3/2.
Cite as

Spyros Angelopoulos, Christoph Dürr, and Shendan Jin. Online Maximum Matching with Recourse. In 43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 117, pp. 8:1-8:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{angelopoulos_et_al:LIPIcs.MFCS.2018.8,
  author =	{Angelopoulos, Spyros and D\"{u}rr, Christoph and Jin, Shendan},
  title =	{{Online Maximum Matching with Recourse}},
  booktitle =	{43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018)},
  pages =	{8:1--8:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-086-6},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{117},
  editor =	{Potapov, Igor and Spirakis, Paul and Worrell, James},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2018.8},
  URN =		{urn:nbn:de:0030-drops-95908},
  doi =		{10.4230/LIPIcs.MFCS.2018.8},
  annote =	{Keywords: Competitive ratio, maximum cardinality matching, recourse}
}
Document
DOI: 10.4230/LIPIcs.ICALP.2018.49
Faster Algorithms for Integer Programs with Block Structure

Authors: Friedrich Eisenbrand, Christoph Hunkenschröder, and Kim-Manuel Klein

Published in: LIPIcs, Volume 107, 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)

Abstract
We consider integer programming problems max {c^Tx : A x = b, l <= x <= u, x in Z^{nt}} where A has a (recursive) block-structure generalizing n-fold integer programs which recently received considerable attention in the literature. An n-fold IP is an integer program where A consists of n repetitions of submatrices A in Z^{r × t} on the top horizontal part and n repetitions of a matrix B in Z^{s × t} on the diagonal below the top part. Instead of allowing only two types of block matrices, one for the horizontal line and one for the diagonal, we generalize the n-fold setting to allow for arbitrary matrices in every block. We show that such an integer program can be solved in time n^2t^2 phi x (r s delta)^{O(rs^2+ sr^2)} (ignoring logarithmic factors). Here delta is an upper bound on the largest absolute value of an entry of A and phi is the largest binary encoding length of a coefficient of c. This improves upon the previously best algorithm of Hemmecke, Onn and Romanchuk that runs in time n^3t^3 phi x delta^{O(st(r+t))}. In particular, our algorithm is not exponential in the number t of columns of A and B. Our algorithm is based on a new upper bound on the l_1-norm of an element of the Graver basis of an integer matrix and on a proximity bound between the LP and IP optimal solutions tailored for IPs with block structure. These new bounds rely on the Steinitz Lemma. Furthermore, we extend our techniques to the recently introduced tree-fold IPs, where we again present a more efficient algorithm in a generalized setting.
Cite as

Friedrich Eisenbrand, Christoph Hunkenschröder, and Kim-Manuel Klein. Faster Algorithms for Integer Programs with Block Structure. In 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 107, pp. 49:1-49:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{eisenbrand_et_al:LIPIcs.ICALP.2018.49,
  author =	{Eisenbrand, Friedrich and Hunkenschr\"{o}der, Christoph and Klein, Kim-Manuel},
  title =	{{Faster Algorithms for Integer Programs with Block Structure}},
  booktitle =	{45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)},
  pages =	{49:1--49:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-076-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{107},
  editor =	{Chatzigiannakis, Ioannis and Kaklamanis, Christos and Marx, D\'{a}niel and Sannella, Donald},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2018.49},
  URN =		{urn:nbn:de:0030-drops-90537},
  doi =		{10.4230/LIPIcs.ICALP.2018.49},
  annote =	{Keywords: n-fold, Tree-fold, Integer Programming}
}
Document
DOI: 10.4230/DagRep.7.11.28
Algorithmic Cheminformatics (Dagstuhl Seminar 17452)

Authors: Jakob L. Andersen, Christoph Flamm, Daniel Merkle, and Peter F. Stadler

Published in: Dagstuhl Reports, Volume 7, Issue 11 (2018)

Abstract
Dagstuhl Seminar 17452 "Algorithmic Cheminformatics" brought together leading researchers from both chemistry and computer science. The seminar was the second in a series of the Dagstuhl seminars and had a focus on concurrency theory as chemical systems are highly concurrent by nature. Within computer science we focused on formal approaches for chemistry and concurrency theory, including process calculi and Petri nets. The participants surveyed areas of overlapping interests and identified possible fields of joint future research.
Cite as

Jakob L. Andersen, Christoph Flamm, Daniel Merkle, and Peter F. Stadler. Algorithmic Cheminformatics (Dagstuhl Seminar 17452). In Dagstuhl Reports, Volume 7, Issue 11, pp. 28-45, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{andersen_et_al:DagRep.7.11.28,
  author =	{Andersen, Jakob L. and Flamm, Christoph and Merkle, Daniel and Stadler, Peter F.},
  title =	{{Algorithmic Cheminformatics (Dagstuhl Seminar 17452)}},
  pages =	{28--45},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2018},
  volume =	{7},
  number =	{11},
  editor =	{Andersen, Jakob L. and Flamm, Christoph and Merkle, Daniel and Stadler, Peter F.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagRep.7.11.28},
  URN =		{urn:nbn:de:0030-drops-86692},
  doi =		{10.4230/DagRep.7.11.28},
  annote =	{Keywords: Modelling, Simulation, Networks, Semantics / Formal Methods}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2017.12
Counting Problems for Parikh Images

Authors: Christoph Haase, Stefan Kiefer, and Markus Lohrey

Published in: LIPIcs, Volume 83, 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017)

Abstract
Given finite-state automata (or context-free grammars) A,B over the same alphabet and a Parikh vector p, we study the complexity of deciding whether the number of words in the language of A with Parikh image p is greater than the number of such words in the language of B. Recently, this problem turned out to be tightly related to the cost problem for weighted Markov chains. We classify the complexity according to whether A and B are deterministic, the size of the alphabet, and the encoding of p (binary or unary).
Cite as

Christoph Haase, Stefan Kiefer, and Markus Lohrey. Counting Problems for Parikh Images. In 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 83, pp. 12:1-12:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{haase_et_al:LIPIcs.MFCS.2017.12,
  author =	{Haase, Christoph and Kiefer, Stefan and Lohrey, Markus},
  title =	{{Counting Problems for Parikh Images}},
  booktitle =	{42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017)},
  pages =	{12:1--12:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-046-0},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{83},
  editor =	{Larsen, Kim G. and Bodlaender, Hans L. and Raskin, Jean-Francois},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2017.12},
  URN =		{urn:nbn:de:0030-drops-80597},
  doi =		{10.4230/LIPIcs.MFCS.2017.12},
  annote =	{Keywords: Parikh images, finite automata, counting problems}
}
Document
DOI: 10.4230/DagMan.6.1.1
Engineering Academic Software (Dagstuhl Perspectives Workshop 16252)

Authors: Alice Allen, Cecilia Aragon, Christoph Becker, Jeffrey Carver, Andrei Chis, Benoit Combemale, Mike Croucher, Kevin Crowston, Daniel Garijo, Ashish Gehani, Carole Goble, Robert Haines, Robert Hirschfeld, James Howison, Kathryn Huff, Caroline Jay, Daniel S. Katz, Claude Kirchner, Katie Kuksenok, Ralf Lämmel, Oscar Nierstrasz, Matt Turk, Rob van Nieuwpoort, Matthew Vaughn, and Jurgen J. Vinju

Published in: Dagstuhl Manifestos, Volume 6, Issue 1 (2017)

Abstract
Software is often a critical component of scientific research. It can be a component of the academic research methods used to produce research results, or it may itself be an academic research result. Software, however, has rarely been considered to be a citable artifact in its own right. With the advent of open-source software, artifact evaluation committees of conferences, and journals that include source code and running systems as part of the published artifacts, we foresee that software will increasingly be recognized as part of the academic process. The quality and sustainability of this software must be accounted for, both a prioro and a posteriori. The Dagstuhl Perspectives Workshop on "Engineering Academic Software" has examined the strengths, weaknesses, risks, and opportunities of academic software engineering. A key outcome of the workshop is this Dagstuhl Manifesto, serving as a roadmap towards future professional software engineering for software-based research instruments and other software produced and used in an academic context. The manifesto is expressed in terms of a series of actionable "pledges" that users and developers of academic research software can take as concrete steps towards improving the environment in which that software is produced.
Cite as

Alice Allen, Cecilia Aragon, Christoph Becker, Jeffrey Carver, Andrei Chis, Benoit Combemale, Mike Croucher, Kevin Crowston, Daniel Garijo, Ashish Gehani, Carole Goble, Robert Haines, Robert Hirschfeld, James Howison, Kathryn Huff, Caroline Jay, Daniel S. Katz, Claude Kirchner, Katie Kuksenok, Ralf Lämmel, Oscar Nierstrasz, Matt Turk, Rob van Nieuwpoort, Matthew Vaughn, and Jurgen J. Vinju. Engineering Academic Software (Dagstuhl Perspectives Workshop 16252). In Dagstuhl Manifestos, Volume 6, Issue 1, pp. 1-20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@Article{allen_et_al:DagMan.6.1.1,
  author =	{Allen, Alice and Aragon, Cecilia and Becker, Christoph and Carver, Jeffrey and Chis, Andrei and Combemale, Benoit and Croucher, Mike and Crowston, Kevin and Garijo, Daniel and Gehani, Ashish and Goble, Carole and Haines, Robert and Hirschfeld, Robert and Howison, James and Huff, Kathryn and Jay, Caroline and Katz, Daniel S. and Kirchner, Claude and Kuksenok, Katie and L\"{a}mmel, Ralf and Nierstrasz, Oscar and Turk, Matt and van Nieuwpoort, Rob and Vaughn, Matthew and Vinju, Jurgen J.},
  title =	{{Engineering Academic Software (Dagstuhl Perspectives Workshop 16252)}},
  pages =	{1--20},
  journal =	{Dagstuhl Manifestos},
  ISSN =	{2193-2433},
  year =	{2017},
  volume =	{6},
  number =	{1},
  editor =	{Allen, Alice and Aragon, Cecilia and Becker, Christoph and Carver, Jeffrey and Chis, Andrei and Combemale, Benoit and Croucher, Mike and Crowston, Kevin and Garijo, Daniel and Gehani, Ashish and Goble, Carole and Haines, Robert and Hirschfeld, Robert and Howison, James and Huff, Kathryn and Jay, Caroline and Katz, Daniel S. and Kirchner, Claude and Kuksenok, Katie and L\"{a}mmel, Ralf and Nierstrasz, Oscar and Turk, Matt and van Nieuwpoort, Rob and Vaughn, Matthew and Vinju, Jurgen J.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagMan.6.1.1},
  URN =		{urn:nbn:de:0030-drops-71468},
  doi =		{10.4230/DagMan.6.1.1},
  annote =	{Keywords: Academic software, Research software, Software citation, Software sustainability}
}
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