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Documents authored by Nowotka, Dirk

Document
DOI: 10.4230/LIPIcs.ISAAC.2023.4
k-Universality of Regular Languages

Authors: Duncan Adamson, Pamela Fleischmann, Annika Huch, Tore Koß, Florin Manea, and Dirk Nowotka

Published in: LIPIcs, Volume 283, 34th International Symposium on Algorithms and Computation (ISAAC 2023)

Abstract
A subsequence of a word w is a word u such that u = w[i₁] w[i₂] … w[i_k], for some set of indices 1 ≤ i₁ < i₂ < … < i_k ≤ |w|. A word w is k-subsequence universal over an alphabet Σ if every word in Σ^k appears in w as a subsequence. In this paper, we study the intersection between the set of k-subsequence universal words over some alphabet Σ and regular languages over Σ. We call a regular language L k-∃-subsequence universal if there exists a k-subsequence universal word in L, and k-∀-subsequence universal if every word of L is k-subsequence universal. We give algorithms solving the problems of deciding if a given regular language, represented by a finite automaton recognising it, is k-∃-subsequence universal and, respectively, if it is k-∀-subsequence universal, for a given k. The algorithms are FPT w.r.t. the size of the input alphabet, and their run-time does not depend on k; they run in polynomial time in the number n of states of the input automaton when the size of the input alphabet is O(log n). Moreover, we show that the problem of deciding if a given regular language is k-∃-subsequence universal is NP-complete, when the language is over a large alphabet. Further, we provide algorithms for counting the number of k-subsequence universal words (paths) accepted by a given deterministic (respectively, nondeterministic) finite automaton, and ranking an input word (path) within the set of k-subsequence universal words accepted by a given finite automaton.
Cite as

Duncan Adamson, Pamela Fleischmann, Annika Huch, Tore Koß, Florin Manea, and Dirk Nowotka. k-Universality of Regular Languages. In 34th International Symposium on Algorithms and Computation (ISAAC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 283, pp. 4:1-4:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{adamson_et_al:LIPIcs.ISAAC.2023.4,
  author =	{Adamson, Duncan and Fleischmann, Pamela and Huch, Annika and Ko{\ss}, Tore and Manea, Florin and Nowotka, Dirk},
  title =	{{k-Universality of Regular Languages}},
  booktitle =	{34th International Symposium on Algorithms and Computation (ISAAC 2023)},
  pages =	{4:1--4:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-289-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{283},
  editor =	{Iwata, Satoru and Kakimura, Naonori},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2023.4},
  URN =		{urn:nbn:de:0030-drops-193064},
  doi =		{10.4230/LIPIcs.ISAAC.2023.4},
  annote =	{Keywords: String Algorithms, Regular Languages, Finite Automata, Subsequences}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2019.44
Upper Bounds on the Length of Minimal Solutions to Certain Quadratic Word Equations

Authors: Joel D. Day, Florin Manea, and Dirk Nowotka

Published in: LIPIcs, Volume 138, 44th International Symposium on Mathematical Foundations of Computer Science (MFCS 2019)

Abstract
It is a long standing conjecture that the problem of deciding whether a quadratic word equation has a solution is in NP. It has also been conjectured that the length of a minimal solution to a quadratic equation is at most exponential in the length of the equation, with the latter conjecture implying the former. We show that both conjectures hold for some natural subclasses of quadratic equations, namely the classes of regular-reversed, k-ordered, and variable-sparse quadratic equations. We also discuss a connection of our techniques to the topic of unavoidable patterns, and the possibility of exploiting this connection to produce further similar results.
Cite as

Joel D. Day, Florin Manea, and Dirk Nowotka. Upper Bounds on the Length of Minimal Solutions to Certain Quadratic Word Equations. In 44th International Symposium on Mathematical Foundations of Computer Science (MFCS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 138, pp. 44:1-44:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{day_et_al:LIPIcs.MFCS.2019.44,
  author =	{Day, Joel D. and Manea, Florin and Nowotka, Dirk},
  title =	{{Upper Bounds on the Length of Minimal Solutions to Certain Quadratic Word Equations}},
  booktitle =	{44th International Symposium on Mathematical Foundations of Computer Science (MFCS 2019)},
  pages =	{44:1--44:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-117-7},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{138},
  editor =	{Rossmanith, Peter and Heggernes, Pinar and Katoen, Joost-Pieter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2019.44},
  URN =		{urn:nbn:de:0030-drops-109889},
  doi =		{10.4230/LIPIcs.MFCS.2019.44},
  annote =	{Keywords: Quadratic Word Equations, Length Upper Bounds, NP, Unavoidable Patterns}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2018.18
Lagrange's Theorem for Binary Squares

Authors: P. Madhusudan, Dirk Nowotka, Aayush Rajasekaran, and Jeffrey Shallit

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

Abstract
We show how to prove theorems in additive number theory using a decision procedure based on finite automata. Among other things, we obtain the following analogue of Lagrange's theorem: every natural number > 686 is the sum of at most 4 natural numbers whose canonical base-2 representation is a binary square, that is, a string of the form xx for some block of bits x. Here the number 4 is optimal. While we cannot embed this theorem itself in a decidable theory, we show that stronger lemmas that imply the theorem can be embedded in decidable theories, and show how automated methods can be used to search for these stronger lemmas.
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P. Madhusudan, Dirk Nowotka, Aayush Rajasekaran, and Jeffrey Shallit. Lagrange's Theorem for Binary Squares. In 43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 117, pp. 18:1-18:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{madhusudan_et_al:LIPIcs.MFCS.2018.18,
  author =	{Madhusudan, P. and Nowotka, Dirk and Rajasekaran, Aayush and Shallit, Jeffrey},
  title =	{{Lagrange's Theorem for Binary Squares}},
  booktitle =	{43rd International Symposium on Mathematical Foundations of Computer Science (MFCS 2018)},
  pages =	{18:1--18:14},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2018.18},
  URN =		{urn:nbn:de:0030-drops-96003},
  doi =		{10.4230/LIPIcs.MFCS.2018.18},
  annote =	{Keywords: binary square, theorem-proving, finite automaton, decision procedure, decidable theory, additive number theory}
}
Document
DOI: 10.4230/LIPIcs.ICALP.2018.18
Rollercoasters and Caterpillars

Authors: Therese Biedl, Ahmad Biniaz, Robert Cummings, Anna Lubiw, Florin Manea, Dirk Nowotka, and Jeffrey Shallit

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

Abstract
A rollercoaster is a sequence of real numbers for which every maximal contiguous subsequence - increasing or decreasing - has length at least three. By translating this sequence to a set of points in the plane, a rollercoaster can be defined as an x-monotone polygonal path for which every maximal sub-path, with positive- or negative-slope edges, has at least three vertices. Given a sequence of distinct real numbers, the rollercoaster problem asks for a maximum-length (not necessarily contiguous) subsequence that is a rollercoaster. It was conjectured that every sequence of n distinct real numbers contains a rollercoaster of length at least ceil[n/2] for n>7, while the best known lower bound is Omega(n/log n). In this paper we prove this conjecture. Our proof is constructive and implies a linear-time algorithm for computing a rollercoaster of this length. Extending the O(n log n)-time algorithm for computing a longest increasing subsequence, we show how to compute a maximum-length rollercoaster within the same time bound. A maximum-length rollercoaster in a permutation of {1,...,n} can be computed in O(n log log n) time. The search for rollercoasters was motivated by orthogeodesic point-set embedding of caterpillars. A caterpillar is a tree such that deleting the leaves gives a path, called the spine. A top-view caterpillar is one of maximum degree 4 such that the two leaves adjacent to each vertex lie on opposite sides of the spine. As an application of our result on rollercoasters, we are able to find a planar drawing of every n-vertex top-view caterpillar on every set of 25/3(n+4) points in the plane, such that each edge is an orthogonal path with one bend. This improves the previous best known upper bound on the number of required points, which is O(n log n). We also show that such a drawing can be obtained in linear time, when the points are given in sorted order.
Cite as

Therese Biedl, Ahmad Biniaz, Robert Cummings, Anna Lubiw, Florin Manea, Dirk Nowotka, and Jeffrey Shallit. Rollercoasters and Caterpillars. In 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 107, pp. 18:1-18:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{biedl_et_al:LIPIcs.ICALP.2018.18,
  author =	{Biedl, Therese and Biniaz, Ahmad and Cummings, Robert and Lubiw, Anna and Manea, Florin and Nowotka, Dirk and Shallit, Jeffrey},
  title =	{{Rollercoasters and Caterpillars}},
  booktitle =	{45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)},
  pages =	{18:1--18:15},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2018.18},
  URN =		{urn:nbn:de:0030-drops-90224},
  doi =		{10.4230/LIPIcs.ICALP.2018.18},
  annote =	{Keywords: sequences, alternating runs, patterns in permutations, caterpillars}
}
Document
DOI: 10.4230/LIPIcs.ICALP.2018.136
An Optimal Bound on the Solution Sets of One-Variable Word Equations and its Consequences

Authors: Dirk Nowotka and Aleksi Saarela

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

Abstract
We solve two long-standing open problems on word equations. Firstly, we prove that a one-variable word equation with constants has either at most three or an infinite number of solutions. The existence of such a bound had been conjectured, and the bound three is optimal. Secondly, we consider independent systems of three-variable word equations without constants. If such a system has a nonperiodic solution, then this system of equations is at most of size 17. Although probably not optimal, this is the first finite bound found. However, the conjecture of that bound being actually two still remains open.
Cite as

Dirk Nowotka and Aleksi Saarela. An Optimal Bound on the Solution Sets of One-Variable Word Equations and its Consequences. In 45th International Colloquium on Automata, Languages, and Programming (ICALP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 107, pp. 136:1-136:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{nowotka_et_al:LIPIcs.ICALP.2018.136,
  author =	{Nowotka, Dirk and Saarela, Aleksi},
  title =	{{An Optimal Bound on the Solution Sets of One-Variable Word Equations and its Consequences}},
  booktitle =	{45th International Colloquium on Automata, Languages, and Programming (ICALP 2018)},
  pages =	{136:1--136:13},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2018.136},
  URN =		{urn:nbn:de:0030-drops-91404},
  doi =		{10.4230/LIPIcs.ICALP.2018.136},
  annote =	{Keywords: combinatorics on words, word equations, systems of equations}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2017.24
Local Patterns

Authors: Joel D. Day, Pamela Fleischmann, Florin Manea, and Dirk Nowotka

Published in: LIPIcs, Volume 93, 37th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2017)

Abstract
A pattern is a word consisting of constants from an alphabet Sigma of terminal symbols and variables from a set X. Given a pattern alpha, the decision-problem whether a given word w may be obtained by substituting the variables in \alpha for words over Sigma is called the matching problem. While this problem is, in general, NP-complete, several classes of patterns for which it can be efficiently solved are already known. We present two new classes of patterns, called k-local, and strongly-nested, and show that the respective matching problems, as well as membership can be solved efficiently for any fixed k.
Cite as

Joel D. Day, Pamela Fleischmann, Florin Manea, and Dirk Nowotka. Local Patterns. In 37th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 93, pp. 24:1-24:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{day_et_al:LIPIcs.FSTTCS.2017.24,
  author =	{Day, Joel D. and Fleischmann, Pamela and Manea, Florin and Nowotka, Dirk},
  title =	{{Local Patterns}},
  booktitle =	{37th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2017)},
  pages =	{24:1--24:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-055-2},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{93},
  editor =	{Lokam, Satya and Ramanujam, R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2017.24},
  URN =		{urn:nbn:de:0030-drops-84013},
  doi =		{10.4230/LIPIcs.FSTTCS.2017.24},
  annote =	{Keywords: Patterns with Variables, Local Patterns, Combinatorial Pattern Matching, Descriptive Patterns}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2017.18
The Hardness of Solving Simple Word Equations

Authors: Joel D. Day, Florin Manea, and Dirk Nowotka

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

Abstract
We investigate the class of regular-ordered word equations. In such equations, each variable occurs at most once in each side and the order of the variables occurring in both left and right hand sides is preserved (the variables can be, however, separated by potentially distinct constant factors). Surprisingly, we obtain that solving such simple equations, even when the sides contain exactly the same variables, is NP-hard. By considerations regarding the combinatorial structure of the minimal solutions of the more general quadratic equations we obtain that the satisfiability problem for regular-ordered equations is in NP. The complexity of solving such word equations under regular constraints is also settled. Finally, we show that a related class of simple word equations, that generalises one-variable equations, is in P.
Cite as

Joel D. Day, Florin Manea, and Dirk Nowotka. The Hardness of Solving Simple Word Equations. In 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 83, pp. 18:1-18:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{day_et_al:LIPIcs.MFCS.2017.18,
  author =	{Day, Joel D. and Manea, Florin and Nowotka, Dirk},
  title =	{{The Hardness of Solving Simple Word Equations}},
  booktitle =	{42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017)},
  pages =	{18:1--18:14},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2017.18},
  URN =		{urn:nbn:de:0030-drops-81233},
  doi =		{10.4230/LIPIcs.MFCS.2017.18},
  annote =	{Keywords: Word Equations, Regular Patterns, Regular Constraints}
}
Document
DOI: 10.4230/DagRep.4.3.28
Combinatorics and Algorithmics of Strings (Dagstuhl Seminar 14111)

Authors: Maxime Crochemore, James D. Currie, Gregory Kucherov, and Dirk Nowotka

Published in: Dagstuhl Reports, Volume 4, Issue 3 (2014)

Abstract
Strings (aka sequences or words) form the most basic and natural data structure. They occur whenever information is electronically transmitted (as bit streams), when natural language text is spoken or written down (as words over, for example, the Latin alphabet), in the process of heredity transmission in living cells (through DNA sequences) or the protein synthesis (as sequence of amino acids), and in many more different contexts. Given this universal form of representing information, the need to process strings is apparent and is actually a core purpose of computer use. Algorithms to efficiently search through, analyze, (de-)compress, match, encode and decode strings are therefore of chief interest. Combinatorial problems about strings lie at the core of such algorithmic questions. Many such combinatorial problems are common in the string processing efforts in the different fields of application. The purpose of this seminar is to bring together researchers from different disciplines whose interests are string processing algorithms and related combinatorial problems on words. The two main areas of interest for this seminar are Combinatorics on Words and Stringology. This report documents the program and the outcomes of Dagstuhl Seminar 14111 "Combinatorics and Algorithmics of Strings".
Cite as

Maxime Crochemore, James D. Currie, Gregory Kucherov, and Dirk Nowotka. Combinatorics and Algorithmics of Strings (Dagstuhl Seminar 14111). In Dagstuhl Reports, Volume 4, Issue 3, pp. 28-46, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@Article{crochemore_et_al:DagRep.4.3.28,
  author =	{Crochemore, Maxime and Currie, James D. and Kucherov, Gregory and Nowotka, Dirk},
  title =	{{Combinatorics and Algorithmics of Strings (Dagstuhl Seminar 14111)}},
  pages =	{28--46},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2014},
  volume =	{4},
  number =	{3},
  editor =	{Crochemore, Maxime and Currie, James D. and Kucherov, Gregory and Nowotka, Dirk},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.4.3.28},
  URN =		{urn:nbn:de:0030-drops-45524},
  doi =		{10.4230/DagRep.4.3.28},
  annote =	{Keywords: combinatorics on words, string algorithms, automata}
}
Document
DOI: 10.4230/LIPIcs.STACS.2014.337
Testing Generalised Freeness of Words

Authors: Pawel Gawrychowski, Florin Manea, and Dirk Nowotka

Published in: LIPIcs, Volume 25, 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)

Abstract
Pseudo-repetitions are a natural generalisation of the classical notion of repetitions in sequences: they are the repeated concatenation of a word and its encoding under a certain morphism or antimorphism (anti-/morphism, for short). We approach the problem of deciding efficiently, for a word w and a literal anti-/morphism f, whether w contains an instance of a given pattern involving a variable x and its image under f, i.e., f(x). Our results generalise both the problem of finding fixed repetitive structures (e.g., squares, cubes) inside a word and the problem of finding palindromic structures inside a word. For instance, we can detect efficiently a factor of the form xx^Rxxx^R, or any other pattern of such type. We also address the problem of testing efficiently, in the same setting, whether the word w contains an arbitrary pseudo-repetition of a given exponent.
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Pawel Gawrychowski, Florin Manea, and Dirk Nowotka. Testing Generalised Freeness of Words. In 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014). Leibniz International Proceedings in Informatics (LIPIcs), Volume 25, pp. 337-349, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{gawrychowski_et_al:LIPIcs.STACS.2014.337,
  author =	{Gawrychowski, Pawel and Manea, Florin and Nowotka, Dirk},
  title =	{{Testing Generalised Freeness of Words}},
  booktitle =	{31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)},
  pages =	{337--349},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-65-1},
  ISSN =	{1868-8969},
  year =	{2014},
  volume =	{25},
  editor =	{Mayr, Ernst W. and Portier, Natacha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2014.337},
  URN =		{urn:nbn:de:0030-drops-44694},
  doi =		{10.4230/LIPIcs.STACS.2014.337},
  annote =	{Keywords: Stringology, Pattern matching, Repetition, Pseudo-repetition}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2013.475
On the Pseudoperiodic Extension of u^l = v^m w^n

Authors: Florin Manea, Mike Müller, and Dirk Nowotka

Published in: LIPIcs, Volume 24, IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2013)

Abstract
We investigate the solution set of the pseudoperiodic extension of the classical Lyndon and Sch\"utzenberger word equations. Consider u_1 ... u_l = v_1 ... v_m w_1 ... w_n, where u_i is in {u, theta(u)} for all 1 <= i <= l, v_j is in {v, theta(v)} for all 1 <= j <= m, w_k is in {w, theta(w)} for all 1 <= k <= n and u, v and w are variables, and theta is an antimorphic involution. A solution is called pseudoperiodic, if u,v,w are in {t, theta(t)}^+ for a word t. [Czeizler et al./I&C/2011] established that for small values of l, m, and n non-periodic solutions exist, and that for large enough values all solutions are pseudoperiodic. However, they leave a gap between those bounds which we close for a number of cases. Namely, we show that for l = 3 and either m,n >= 12 or m,n >= 5 and either m and n are not both even or not all u_i's are equal, all solutions are pseudoperiodic.
Cite as

Florin Manea, Mike Müller, and Dirk Nowotka. On the Pseudoperiodic Extension of u^l = v^m w^n. In IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2013). Leibniz International Proceedings in Informatics (LIPIcs), Volume 24, pp. 475-486, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)

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@InProceedings{manea_et_al:LIPIcs.FSTTCS.2013.475,
  author =	{Manea, Florin and M\"{u}ller, Mike and Nowotka, Dirk},
  title =	{{On the Pseudoperiodic Extension of u^l = v^m w^n}},
  booktitle =	{IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2013)},
  pages =	{475--486},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-64-4},
  ISSN =	{1868-8969},
  year =	{2013},
  volume =	{24},
  editor =	{Seth, Anil and Vishnoi, Nisheeth K.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2013.475},
  URN =		{urn:nbn:de:0030-drops-43948},
  doi =		{10.4230/LIPIcs.FSTTCS.2013.475},
  annote =	{Keywords: Word equations, Pseudoperiodicity, Lyndon-Sch\"{u}tzenberger equation}
}
Document
DOI: 10.4230/LIPIcs.STACS.2013.257
Finding Pseudo-repetitions

Authors: Pawel Gawrychowski, Florin Manea, Robert Mercas, Dirk Nowotka, and Catalin Tiseanu

Published in: LIPIcs, Volume 20, 30th International Symposium on Theoretical Aspects of Computer Science (STACS 2013)

Abstract
Pseudo-repetitions are a natural generalization of the classical notion of repetitions in sequences. We solve fundamental algorithmic questions on pseudo-repetitions by application of insightful combinatorial results on words. More precisely, we efficiently decide whether a word is a pseudo-repetition and find all the pseudo-repetitive factors of a word.
Cite as

Pawel Gawrychowski, Florin Manea, Robert Mercas, Dirk Nowotka, and Catalin Tiseanu. Finding Pseudo-repetitions. In 30th International Symposium on Theoretical Aspects of Computer Science (STACS 2013). Leibniz International Proceedings in Informatics (LIPIcs), Volume 20, pp. 257-268, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)

Copy BibTex To Clipboard

@InProceedings{gawrychowski_et_al:LIPIcs.STACS.2013.257,
  author =	{Gawrychowski, Pawel and Manea, Florin and Mercas, Robert and Nowotka, Dirk and Tiseanu, Catalin},
  title =	{{Finding Pseudo-repetitions}},
  booktitle =	{30th International Symposium on Theoretical Aspects of Computer Science (STACS 2013)},
  pages =	{257--268},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-50-7},
  ISSN =	{1868-8969},
  year =	{2013},
  volume =	{20},
  editor =	{Portier, Natacha and Wilke, Thomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2013.257},
  URN =		{urn:nbn:de:0030-drops-39394},
  doi =		{10.4230/LIPIcs.STACS.2013.257},
  annote =	{Keywords: Stringology, Pattern matching, Repetition, Pseudo-repetition}
}
Document
DOI: 10.4230/DagRep.1.2.47
Combinatorial and Algorithmic Aspects of Sequence Processing (Dagstuhl Seminar 11081)

Authors: Maxime Crochemore, Lila Kari, Mehryar Mohri, and Dirk Nowotka

Published in: Dagstuhl Reports, Volume 1, Issue 2 (2011)

Abstract
Sequences form the most basic and natural data structure. They occur whenever information is electronically transmitted (as bit streams), when natural language text is spoken or written down (as words over, for example, the latin alphabet), in the process of heredity transmission in living cells (as DNA sequence) or the protein synthesis (as sequence of amino acids), and in many more different contexts. Given this universal form of representing information, the need to process strings is apparent and actually a core purpose of computer use. Algorithms to efficiently search through, analyze, (de-)compress, match, learn, and encode/decode strings are therefore of chief interest. Combinatorial problems about strings lie at the core of such algorithmic questions. Many such combinatorial problems are common in the string processing efforts in the different fields of application. Scientists working in the fields of Combinatorics on Words, Computational Biology, Stringology, Natural Computing, and Machine Learning were invited to consider the seminar's topic from a~wide range of perspectives. This report documents the program and the outcomes of Dagstuhl Seminar 11081 ``Combinatorial and Algorithmic Aspects of Sequence Processing''.
Cite as

Maxime Crochemore, Lila Kari, Mehryar Mohri, and Dirk Nowotka. Combinatorial and Algorithmic Aspects of Sequence Processing (Dagstuhl Seminar 11081). In Dagstuhl Reports, Volume 1, Issue 2, pp. 47-66, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2011)

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@Article{crochemore_et_al:DagRep.1.2.47,
  author =	{Crochemore, Maxime and Kari, Lila and Mohri, Mehryar and Nowotka, Dirk},
  title =	{{Combinatorial and Algorithmic Aspects of Sequence Processing (Dagstuhl Seminar 11081)}},
  pages =	{47--66},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2011},
  volume =	{1},
  number =	{2},
  editor =	{Crochemore, Maxime and Kari, Lila and Mohri, Mehryar and Nowotka, Dirk},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.1.2.47},
  URN =		{urn:nbn:de:0030-drops-31554},
  doi =		{10.4230/DagRep.1.2.47},
  annote =	{Keywords: Combinatorics on words, computational biology, stringology, natural computing, machine learning}
}
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