liu.seSearch for publications in DiVA
Change search
Refine search result
1 - 6 of 6
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Fulla, Peter
    et al.
    Univ Oxford, England.
    Uppman, Hannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Zivny, Stanislav
    Univ Oxford, England.
    The Complexity of Boolean Surjective General-Valued CSPs2019In: ACM Transactions on Computation Theory, ISSN 1942-3454, E-ISSN 1942-3462, Vol. 11, no 1, article id 4Article in journal (Refereed)
    Abstract [en]

    Valued constraint satisfaction problems (VCSPs) are discrete optimisation problems with a (Q boolean OR{infinity})-valued objective function given as a sum of fixed-arity functions. In Boolean surjective VCSPs, variables take on labels from D = {0, 1}, and an optimal assignment is required to use both labels from D. Examples include the classical global Min-Cut problem in graphs and the Minimum Distance problem studied in coding theory. We establish a dichotomy theorem and thus give a complete complexity classification of Boolean surjective VCSPs with respect to exact solvability. Our work generalises the dichotomy for {0, infinity}-valued constraint languages (corresponding to surjective decision CSPs) obtained by Creignou and Hebrard. For the maximisation problem of Q(amp;gt;= 0)-valued surjective VCSPs, we also establish a dichotomy theorem with respect to approximability. Unlike in the case of Boolean surjective (decision) CSPs, there appears a novel tractable class of languages that is trivial in the non-surjective setting. This newly discovered tractable class has an interesting mathematical structure related to downsets and upsets. Our main contribution is identifying this class and proving that it lies on the borderline of tractability. A crucial part of our proof is a polynomial-time algorithm for enumerating all near-optimal solutions to a generalised Min-Cut problem, which might be of independent interest.

  • 2.
    Jonsson, Peter
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Lagerkvist, Victor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Schmidt, Johannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Uppman, Hannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Relating the Time Complexity of Optimization Problems in Light of the Exponential-Time Hypothesis2014In: Mathematical Foundations of Computer Science 2014: 39th International Symposium, MFCS 2014, Budapest, Hungary, August 25-29, 2014. Proceedings, Part II / [ed] Erzsébet Csuhaj-Varjú, Martin Dietzfelbinger, Zoltán Ésik, Springer Berlin/Heidelberg, 2014, p. 408-419Conference paper (Refereed)
    Abstract [en]

    Obtaining lower bounds for NP-hard problems has for a long time been an active area of research. Recent algebraic techniques introduced by Jonsson et al. (SODA 2013) show that the time complexity of the parameterized SAT(·) problem correlates to the lattice of strong partial clones. With this ordering they isolated a relation R such that SAT(R) can be solved at least as fast as any other NP-hard SAT(·) problem. In this paper we extend this method and show that such languages also exist for the max ones problem (Max-Ones(Γ)) and the Boolean valued constraint satisfaction problem over finite-valued constraint languages (VCSP(Δ)). With the help of these languages we relate Max-Ones and VCSP to the exponential time hypothesis in several different ways.

    Download full text (pdf)
    fulltext
  • 3.
    Uppman, Hannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Computational Complexity of the Minimum Cost Homomorphism Problem on Three-element Domains2014Conference paper (Refereed)
    Abstract [en]

    In this paper we study the computational complexity of the extended minimum cost homomorphism problem (Min-Cost-Hom) as a function of a constraint language, i.e. a set of constraint relations and cost functions that are allowed to appear in instances. A wide range of natural combinatorial optimisation problems can be expressed as extended Min-Cost-Homs and a classification of their complexity would be highly desirable, both from a direct, applied point of view as well as from a theoretical perspective.

    The extended Min-Cost-Hom can be understood either as a flexible optimisation version of the constraint satisfaction problem (CSP) or a restriction of the (general-valued) valued constraint satisfaction problem (VCSP). Other optimisation versions of CSPs such as the minimum solution problem (Min-Sol) and the minimum ones problem (Min-Ones) are special cases of the extended Min-Cost-Hom.

    The study of VCSPs has recently seen remarkable progress. A complete classification for the complexity of finite-valued languages on arbitrary finite domains has been obtained Thapper and Živný [STOC’13]. However, understanding the complexity of languages that are not finitevalued appears to be more difficult. The extended Min-Cost-Hom allows us to study problematic languages of this type without having to deal with with the full generality of the VCSP. A recent classification for the complexity of three-element Min-Sol, Uppman [ICALP’13], takes a step in this direction. In this paper we generalise this result considerably by determining the complexity of three-element extended Min-Cost-Hom.

  • 4.
    Uppman, Hannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Max-Sur-CSP on Two Elements2012In: Principles and Practice of Constraint Programming: 18th International Conference, CP 2012, Québec City, QC, Canada, October 8-12, 2012. Proceedings / [ed] Michela Milano, Springer Berlin Heidelberg , 2012, p. 38-54Conference paper (Refereed)
    Abstract [en]

    Max-Sur-CSP is the following optimisation problem: given a set of constraints, find a surjective mapping of the variables to domain values that satisfies as many of the constraints as possible. Many natural problems, e.g. Minimum k-Cut (which has many different applications in a variety of fields) and Minimum Distance (which is an important problem in coding theory), can be expressed as Max-Sur-CSPs. We study Max-Sur-CSP on the two-element domain and determine the computational complexity for all constraint languages (families of allowed constraints). Our results show that the problem is solvable in polynomial time if the constraint language belongs to one of three classes, and NP-hard otherwise. An important part of our proof is a polynomial-time algorithm for enumerating all near-optimal solutions to a generalised minimum cut problem. This algorithm may be of independent interest.

  • 5. Order onlineBuy this publication >>
    Uppman, Hannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    On Some Combinatorial Optimization Problems: Algorithms and Complexity2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is about the computational complexity of several classes of combinatorial optimization problems, all related to the constraint satisfaction problems.

    A constraint language consists of a domain and a set of relations on the domain. For each such language there is a constraint satisfaction problem (CSP). In this problem we are given a set of variables and a collection of constraints, each of which is constraining some variables with a relation in the language. The goal is to determine if domain values can be assigned to the variables in a way that satisfies all constraints. An important question is for which constraint languages the corresponding CSP can be solved in polynomial time. We study this kind of question for optimization problems related to the CSPs.

    The main focus is on extended minimum cost homomorphism problems. These are optimization versions of CSPs where instances come with an objective function given by a weighted sum of unary cost functions, and where the goal is not only to determine if a solution exists, but to find one of minimum cost. We prove a complete classification of the complexity for these problems on three-element domains. We also obtain a classification for the so-called conservative case.

    Another class of combinatorial optimization problems are the surjective maximum CSPs. These problems are variants of CSPs where a non-negative weight is attached to each constraint, and the objective is to find a surjective mapping of the variables to values that maximizes the weighted sum of satisfied constraints. The surjectivity requirement causes these problems to behave quite different from for example the minimum cost homomorphism problems, and many powerful techniques are not applicable. We prove a dichotomy for the complexity of the problems in this class on two-element domains. An essential ingredient in the proof is an algorithm that solves a generalized version of the minimum cut problem. This algorithm might be of independent interest.

    In a final part we study properties of NP-hard optimization problems. This is done with the aid of restricted forms of polynomial-time reductions that for example preserves solvability in sub-exponential time. Two classes of optimization problems similar to those discussed above are considered, and for both we obtain what may be called an easiest NP-hard problem. We also establish some connections to the exponential time hypothesis.

    List of papers
    1. Max-Sur-CSP on Two Elements
    Open this publication in new window or tab >>Max-Sur-CSP on Two Elements
    2012 (English)In: Principles and Practice of Constraint Programming: 18th International Conference, CP 2012, Québec City, QC, Canada, October 8-12, 2012. Proceedings / [ed] Michela Milano, Springer Berlin Heidelberg , 2012, p. 38-54Conference paper, Published paper (Refereed)
    Abstract [en]

    Max-Sur-CSP is the following optimisation problem: given a set of constraints, find a surjective mapping of the variables to domain values that satisfies as many of the constraints as possible. Many natural problems, e.g. Minimum k-Cut (which has many different applications in a variety of fields) and Minimum Distance (which is an important problem in coding theory), can be expressed as Max-Sur-CSPs. We study Max-Sur-CSP on the two-element domain and determine the computational complexity for all constraint languages (families of allowed constraints). Our results show that the problem is solvable in polynomial time if the constraint language belongs to one of three classes, and NP-hard otherwise. An important part of our proof is a polynomial-time algorithm for enumerating all near-optimal solutions to a generalised minimum cut problem. This algorithm may be of independent interest.

    Place, publisher, year, edition, pages
    Springer Berlin Heidelberg, 2012
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 7514
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-79515 (URN)10.1007/978-3-642-33558-7_6 (DOI)978-3-642-33557-0 (ISBN)978-3-642-33558-7 (ISBN)
    Conference
    18th International Conference on Principles and Practice of Constraint Programming (CP-2012), 8-12 October, Québec City, Canada
    Available from: 2012-08-06 Created: 2012-08-06 Last updated: 2018-07-17Bibliographically approved
    2. The Complexity of Three-Element Min-Sol and Conservative Min-Cost-Hom
    Open this publication in new window or tab >>The Complexity of Three-Element Min-Sol and Conservative Min-Cost-Hom
    2013 (English)In: Automata, Languages, and Programming: 40th International Colloquium, ICALP 2013, Riga, Latvia, July 8-12, 2013, Proceedings, Part I / [ed] Fedor V. Fomin, Rūsiņš Freivalds, Marta Kwiatkowska, David Peleg, Springer Berlin/Heidelberg, 2013, p. 804-815Conference paper, Published paper (Refereed)
    Abstract [en]

    Thapper and Živný [STOC’13] recently classified the complexity of VCSP for all finite-valued constraint languages. However, the complexity of VCSPs for constraint languages that are not finite-valued remains poorly understood. In this paper we study the complexity of two such VCSPs, namely Min-Cost-Hom and Min-Sol. We obtain a full classification for the complexity of Min-Sol on domains that contain at most three elements and for the complexity of conservative Min-Cost-Hom on arbitrary finite domains. Our results answer a question raised by Takhanov [STACS’10, COCOON’10].

    Place, publisher, year, edition, pages
    Springer Berlin/Heidelberg, 2013
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 7965
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-102664 (URN)10.1007/978-3-642-39206-1_68 (DOI)000342686600068 ()978-3-642-39205-4 (ISBN)978-3-642-39206-1 (ISBN)
    Conference
    40th International Colloquium, ICALP 2013, Riga, Latvia, July 8-12, 2013
    Available from: 2013-12-18 Created: 2013-12-18 Last updated: 2018-07-17Bibliographically approved
    3. Computational Complexity of the Minimum Cost Homomorphism Problem on Three-element Domains
    Open this publication in new window or tab >>Computational Complexity of the Minimum Cost Homomorphism Problem on Three-element Domains
    2014 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    In this paper we study the computational complexity of the extended minimum cost homomorphism problem (Min-Cost-Hom) as a function of a constraint language, i.e. a set of constraint relations and cost functions that are allowed to appear in instances. A wide range of natural combinatorial optimisation problems can be expressed as extended Min-Cost-Homs and a classification of their complexity would be highly desirable, both from a direct, applied point of view as well as from a theoretical perspective.

    The extended Min-Cost-Hom can be understood either as a flexible optimisation version of the constraint satisfaction problem (CSP) or a restriction of the (general-valued) valued constraint satisfaction problem (VCSP). Other optimisation versions of CSPs such as the minimum solution problem (Min-Sol) and the minimum ones problem (Min-Ones) are special cases of the extended Min-Cost-Hom.

    The study of VCSPs has recently seen remarkable progress. A complete classification for the complexity of finite-valued languages on arbitrary finite domains has been obtained Thapper and Živný [STOC’13]. However, understanding the complexity of languages that are not finitevalued appears to be more difficult. The extended Min-Cost-Hom allows us to study problematic languages of this type without having to deal with with the full generality of the VCSP. A recent classification for the complexity of three-element Min-Sol, Uppman [ICALP’13], takes a step in this direction. In this paper we generalise this result considerably by determining the complexity of three-element extended Min-Cost-Hom.

    Place, publisher, year, edition, pages
    Dagstuhl: Schloss Dagstuhl-Leibniz-Zentrum fuer Informatik, 2014
    Series
    Leibniz International Proceedings in Informatics, ISSN 1868-8969 ; 25
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:liu:diva-112916 (URN)10.4230/LIPIcs.STACS.2014.651 (DOI)978-3-939897-65-1 (ISBN)
    Conference
    31st International Symposium on Theoretical Aspects of Computer Science (STACS-2014)
    Available from: 2014-12-19 Created: 2014-12-19 Last updated: 2018-01-11
    4. Relating the Time Complexity of Optimization Problems in Light of the Exponential-Time Hypothesis
    Open this publication in new window or tab >>Relating the Time Complexity of Optimization Problems in Light of the Exponential-Time Hypothesis
    2014 (English)In: Mathematical Foundations of Computer Science 2014: 39th International Symposium, MFCS 2014, Budapest, Hungary, August 25-29, 2014. Proceedings, Part II / [ed] Erzsébet Csuhaj-Varjú, Martin Dietzfelbinger, Zoltán Ésik, Springer Berlin/Heidelberg, 2014, p. 408-419Conference paper, Published paper (Refereed)
    Abstract [en]

    Obtaining lower bounds for NP-hard problems has for a long time been an active area of research. Recent algebraic techniques introduced by Jonsson et al. (SODA 2013) show that the time complexity of the parameterized SAT(·) problem correlates to the lattice of strong partial clones. With this ordering they isolated a relation R such that SAT(R) can be solved at least as fast as any other NP-hard SAT(·) problem. In this paper we extend this method and show that such languages also exist for the max ones problem (Max-Ones(Γ)) and the Boolean valued constraint satisfaction problem over finite-valued constraint languages (VCSP(Δ)). With the help of these languages we relate Max-Ones and VCSP to the exponential time hypothesis in several different ways.

    Place, publisher, year, edition, pages
    Springer Berlin/Heidelberg, 2014
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743, E-ISSN 1611-3349 ; 8635
    National Category
    Computer and Information Sciences
    Identifiers
    urn:nbn:se:liu:diva-112902 (URN)10.1007/978-3-662-44465-8_35 (DOI)000358254600035 ()2-s2.0-84906261436 (Scopus ID)978-3-662-44464-1 (ISBN)978-3-662-44465-8 (ISBN)
    Conference
    39th International Symposium on Mathematical Foundations of Computer Science (MFCS-2014)
    Available from: 2014-12-19 Created: 2014-12-19 Last updated: 2018-07-17Bibliographically approved
    Download full text (pdf)
    fulltext
    Download (pdf)
    omslag
    Download (jpg)
    presentationsbild
  • 6.
    Uppman, Hannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    The Complexity of Three-Element Min-Sol and Conservative Min-Cost-Hom2013In: Automata, Languages, and Programming: 40th International Colloquium, ICALP 2013, Riga, Latvia, July 8-12, 2013, Proceedings, Part I / [ed] Fedor V. Fomin, Rūsiņš Freivalds, Marta Kwiatkowska, David Peleg, Springer Berlin/Heidelberg, 2013, p. 804-815Conference paper (Refereed)
    Abstract [en]

    Thapper and Živný [STOC’13] recently classified the complexity of VCSP for all finite-valued constraint languages. However, the complexity of VCSPs for constraint languages that are not finite-valued remains poorly understood. In this paper we study the complexity of two such VCSPs, namely Min-Cost-Hom and Min-Sol. We obtain a full classification for the complexity of Min-Sol on domains that contain at most three elements and for the complexity of conservative Min-Cost-Hom on arbitrary finite domains. Our results answer a question raised by Takhanov [STACS’10, COCOON’10].

1 - 6 of 6
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf