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  • 251.
    Haller, Philipp
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Sommar, Fredrik
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Towards an Empirical Study of Affine Types for Isolated Actors in Scala2017In: Electronic Proceedings in Theoretical Computer Science, E-ISSN 2075-2180, no 246, p. 3-9Article in journal (Refereed)
    Abstract [en]

    LaCasa is a type system and programming model to enforce the object capability discipline in Scala, and to provide affine types. One important application of LaCasa's type system is software isolation of concurrent processes. Isolation is important for several reasons including security and data-race freedom. Moreover, LaCasa's affine references enable efficient, by-reference message passing while guaranteeing a "deep-copy" semantics. This deep-copy semantics enables programmers to seamlessly port concurrent programs running on a single machine to distributed programs running on large-scale clusters of machines. This paper presents an integration of LaCasa with actors in Scala, specifically, the Akka actor-based middleware, one of the most widely-used actor systems in industry. The goal of this integration is to statically ensure the isolation of Akka actors. Importantly, we present the results of an empirical study investigating the effort required to use LaCasa's type system in existing open-source Akka-based systems and applications.

  • 252. Hansen, Preben
    et al.
    Järvelin, Anni
    Eriksson, Gunnar
    Karlgren, Jussi
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    A Use Case Framework for Information Access Evaluation2014In: Professional Search in the Modern World: COST Action IC1002 on Multilingual and Multifaceted Interactive Information Access / [ed] Paltoglou, Georgios, Loizides, Fernando, Hansen, Preben, Springer, 2014, p. 6-22Chapter in book (Refereed)
    Abstract [en]

    Information access is no longer only a question of retrieving topical text documents in a work-task related context. Information search has become one of the most common uses of the personal computers; a daily task for millions of individual users searching for information motivated by information needs they experience for some reason, momentarily or continuously. Instead of professionally edited text documents, multilingual and multimedia content from a variety of sources of varying quality needs to be accessed. Even the scope of the research efforts in the field must therefore be broadened to better capture the mechanisms for the systems’ impact, take-up and success in the marketplace. Much work has been carried out in this direction: graded relevance, and new evaluation metrics, more varied document collections used in evaluation and different search tasks evaluated. The research in the field is however fragmented. Despite that the need for a common evaluation framework is widely acknowledged, such framework is still not in place. IR system evaluation results are not regularly validated in Interactive IR or field studies; the infrastructure for generalizing Interactive IR results over tasks, users and collections is still missing. This chapter presents a use case-based framework for experimental design in the field of interactive information access. Use cases in general connect system design and evaluation to interaction and user goals, and help identifying test cases for different user groups of a system. We suggest that use cases can provide a useful link even between information access system usage and evaluation mechanisms and thus bring together research from the different related research fields. In this chapter we discuss how use cases can guide the developments of rich models of users, domains, environments, and interaction, and make explicit how the models are connected to benchmarking mechanisms. We give examples of the central features of the different models. The framework is highlighted by examples that sketch out how the framework can be productively used in experimental design and reporting with a minimal threshold for adoption.

  • 253.
    Heintz, Fredrik
    et al.
    Linköping University.
    Berglund, Aseel
    Linköping University.
    Hedin, Björn
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Kann, Viggo
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    En jämförelse mellan programsammanhållande kurser vid KTH och LiU2015Conference paper (Refereed)
    Abstract [sv]

    Programsammanhållande kurser där studenter från årskurs 1-3 gemensamt reflekterar över teman med koppling till deras studier och framtida yrkesliv finns på både KTH och Linköpings universitet (LiU). Syftet med kurserna är främst att skapa en helhet i utbildningen och ge förståelse för vad den leder till, genom att få studenterna att reflektera över sina studier och sin kommande yrkesroll. Detta leder förhoppningsvis till ökad genomströmning och minskade avhopp. Kurserna har gemensamt ursprung men har utvecklats i olika riktningar. Artikeln jämför tre programsammanhållande kurser för Datateknik KTH, Medieteknik KTH samt Data- och mjukvaruteknik Linköpings universitet.

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  • 254. Henzinger, M.
    et al.
    Krinninger, S.
    Na Nongkai, Danupon
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    A deterministic almost-tight distributed algorithm for approximating single-source shortest paths2016In: Proceedings of the Annual ACM Symposium on Theory of Computing, Association for Computing Machinery (ACM), 2016, p. 489-498Conference paper (Refereed)
    Abstract [en]

    We present a deterministic (1+o(1))-approximation O(n1/2+(1) + D1+o(1))-time algorithm for solving the single-source shortest paths problem on distributed weighted networks (the CONGEST model); here n is the number of nodes in the network and D is its (hop) diameter. This is the first non-trivial deterministic algorithm for this problem. It also improves (i) the running time of the randomized (1 + o(1))-approximation Õ(n1/2 D1/4+ D)-time algorithm of Nanongkai [STOC 2014] by a factor of as large as n1/8, and (ii) the O(ϵ-1 log ϵ-1)-approximation factor of Lenzen and Patt-Shamir's Õ (n1/2+∈ + D)-time algorithm [STOC 2013] within the same running time. Our running time matches the known time lower bound of Ω(n1/2/log n + D) [Das Sarma et al., STOC 2011] modulo some lower-order terms, thus essentially settling the status of this problem which was raised at least a decade ago [Elkin, SIGACT News 2004]. It also implies a (2 + o(1))-approximation O(n1/2+o(1) + D1+o(1)-time algorithm for approximating a network's weighted diameter which almost matches the lower bound by Holzer et al. [PODC 2012]. In achieving this result, we develop two techniques which might be of independent interest and useful in other settings: (i) a deterministic process that replaces the "hitting set argument" commonly used for shortest paths computation in various settings, and (ii) a simple, deterministic, construction of an (no(1), o(1))-hop set of size O(n1+o(1)). We combine these techniques with many distributed algorithmic techniques, some of which from problems that are not directly related to shortest paths, e.g. ruling sets [26], source detection [39], and partial distance estimation [38]. Our hop set construction also leads to single-source shortest paths algorithms in two other settings: (i) a (1 + o(1))-approximation O(no(1))-time algorithm on congested cliques, and (ii) a (1 + o(1))-approximation O(no(1) log W)-pass O(n1+o(1) log W)-space streaming algorithm, when edge weights are in {1,2,..., W}. The first result answers an open problem in [Nanongkai, STOC 2014]. The second result partially answers an open problem raised by McGregor in 2006 [sublinear.info, Problem 14].

  • 255.
    Henzinger, Monika
    et al.
    University of Vienna.
    Krinninger, Sebastian
    University of Vienna.
    Na Nongkai, Danupon
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Saranurak, Thatchaphol
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Unifying and Strengthening Hardness for Dynamic Problems via the Online Matrix-Vector Multiplication Conjecture2015In: STOC '15 Proceedings of the Forty-Seventh Annual ACM on Symposium on Theory of Computing, ACM Press, 2015, p. 21-30Conference paper (Refereed)
    Abstract [en]

    Consider the following Online Boolean Matrix-Vector Multiplication problem: We are given an n x n matrix M and will receive n column-vectors of size n, denoted by v1, ..., vn, one by one. After seeing each vector vi, we have to output the product Mvi before we can see the next vector. A naive algorithm can solve this problem using O(n3) time in total, and its running time can be slightly improved to O(n3/log2 n) [Williams SODA'07]. We show that a conjecture that there is no truly subcubic (O(n3-ε)) time algorithm for this problem can be used to exhibit the underlying polynomial time hardness shared by many dynamic problems. For a number of problems, such as subgraph connectivity, Pagh's problem, d-failure connectivity, decremental single-source shortest paths, and decremental transitive closure, this conjecture implies tight hardness results. Thus, proving or disproving this conjecture will be very interesting as it will either imply several tight unconditional lower bounds or break through a common barrier that blocks progress with these problems. This conjecture might also be considered as strong evidence against any further improvement for these problems since refuting it will imply a major breakthrough for combinatorial Boolean matrix multiplication and other long-standing problems if the term "combinatorial algorithms" is interpreted as "Strassen-like algorithms" [Ballard et al. SPAA'11].

    The conjecture also leads to hardness results for problems that were previously based on diverse problems and conjectures -- such as 3SUM, combinatorial Boolean matrix multiplication, triangle detection, and multiphase -- thus providing a uniform way to prove polynomial hardness results for dynamic algorithms; some of the new proofs are also simpler or even become trivial. The conjecture also leads to stronger and new, non-trivial, hardness results, e.g., for the fully-dynamic densest subgraph and diameter problems.

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  • 256. Henzinger, Monika
    et al.
    Krinninger, Sebastian
    Nanongkai, Danupon
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Improved Algorithms for Decremental Single-Source Reachability on Directed Graphs2015In: Automata, Languages, and Programming: 42nd International Colloquium, ICALP 2015, Kyoto, Japan, July 6-10, 2015, Proceedings, Part I, Springer Berlin/Heidelberg, 2015, p. 725-736Conference paper (Refereed)
    Abstract [en]

    Recently we presented the first algorithm for maintaining the set of nodes reachable from a source node in a directed graph that is modified by edge deletions with o(mn)  total update time, where m  is the number of edges and n  is the number of nodes in the graph [Henzinger et al. STOC 2014]. The algorithm is a combination of several different algorithms, each for a different m  vs. n  trade-off. For the case of m=Θ(n 1.5 )  the running time is O(n 2.47 )  , just barely below mn=Θ(n 2.5 )  . In this paper we simplify the previous algorithm using new algorithmic ideas and achieve an improved running time of O ~ (min(m 7/6 n 2/3 ,m 3/4 n 5/4+o(1) ,m 2/3 n 4/3+o(1) +m 3/7 n 12/7+o(1) )) . This gives, e.g., O(n 2.36 )  for the notorious case m=Θ(n 1.5 ) . We obtain the same upper bounds for the problem of maintaining the strongly connected components of a directed graph undergoing edge deletions. Our algorithms are correct with high probabililty against an oblivious adversary.

  • 257. Henzinger, Monika
    et al.
    Krinninger, Sebastian
    Nanongkai, Danupon
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS. University of Vienna, Austria.
    Sublinear-Time Maintenance of Breadth-First Spanning Trees in Partially Dynamic Networks2017In: ACM Transactions on Algorithms, ISSN 1549-6325, E-ISSN 1549-6333, Vol. 13, no 4, article id 51Article in journal (Refereed)
    Abstract [en]

    We study the problem of maintaining a breadth-first spanning tree (BFS tree) in partially dynamic distributed networks modeling a sequence of either failures or additions of communication links (but not both). We present deterministic (1 + is an element of)-approximation algorithms whose amortized time (over some number of link changes) is sublinear in D, the maximum diameter of the network. Our technique also leads to a deterministic (1 + is an element of)-approximate incremental algorithm for single-source shortest paths in the sequential (usual RAM) model. Prior to our work, the state of the art was the classic exact algorithm of Even and Shiloach (1981), which is optimal under some assumptions (Roditty and Zwick 2011; Henzinger et al. 2015). Our result is the first to show that, in the incremental setting, this bound can be beaten in certain cases if some approximation is allowed.

  • 258.
    Hidell, Markus
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Sjödin, Peter
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture, Telecommunication Systems Laboratory, TSLab.
    Hagsand, Olof
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    NACK-Oriented Reliable Multicast for Routing Table Distribution in Decentralized Routers2005In: 3rd Swedish National Computer Networking Workshop, SNCNW 2005, Halmstad, Sweden, 2005Conference paper (Refereed)
    Abstract [en]

    The requirements on IP routers are increasing for every new generation of designs. The driving forces behind this development are growing traffic volumes and demands for new services. We believe that a modular decentralized router design is well-suited to meet future requirements. However, a distributed design may, compared to a centralized system, introduce an additional cost for internal communication between the elements. In this paper we evaluate different transaction mechanisms for the internal communication. We study the suitability of reliable multicast for the internal distribution of large amounts of routing information. In particular, we evaluate NORM (NACK-Oriented Reliable Multicast) as a candidate protocol for our purposes.

  • 259. Hirsch, D.
    et al.
    Markström, Ingemar
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Patterson, M. L.
    Sandberg, A.
    Vejdemo-Johansson, Mikael
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP. Jožef Štefan Institute, Slovenia.
    More ties than we thought2015In: PeerJ, E-ISSN 2167-8359, Vol. 2015, no 1, article id e2Article in journal (Refereed)
    Abstract [en]

    We extend the existing enumeration of neck tie-knots to include tie-knots with a textured front, tied with the narrow end of a tie. These tie-knots have gained popularity in recent years, based on reconstructions of a costume detail from The Matrix Reloaded, and are explicitly ruled out in the enumeration by Fink & Mao (2000). We show that the relaxed tie-knot description language that comprehensively describes these extended tie-knot classes is context free. It has a regular sub-language that covers all the knots that originally inspired the work. From the full language, we enumerate 266,682 distinct tie-knots that seem tie-able with a normal neck-tie. Out of these 266,682, we also enumerate 24,882 tie-knots that belong to the regular sub-language.

  • 260. Howar, Falk
    et al.
    Meinke, Karl
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Rausch, Andreas
    Learning Systems: Machine-Learning in Software Products and Learning-Based Analysis of Software Systems Special Track at ISoLA 20162016In: LEVERAGING APPLICATIONS OF FORMAL METHODS, VERIFICATION AND VALIDATION: DISCUSSION, DISSEMINATION, APPLICATIONS, ISOLA 2016, PT II, 2016, p. 651-654Conference paper (Refereed)
  • 261. Hu, S.
    et al.
    Meinke, Karl
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Dynamic-measurement modeling of attitude motion for N-bodies spacecraft with applications2011In: Proceedings of the 30th Chinese Control Conference, 2011, p. 1453-1458Conference paper (Refereed)
    Abstract [en]

    Modeling analysis technique is one of the most important means in processing spaceflight mission. In this paper, the graph based description is given, and a series of dynamic-measurement system models are built for the attitude motion of a N-bodies spacecraft, which include the states evolvement equation of the main body, the states evolvement equations of the accessories, the inertia based measurement equations and the celestial bodies based measurement equation and the GPS based measurement equations of attitudes of the N-bodies etc.. These models are educed with some typical methods of theoretical analysis and dynamic description and are simplified into linearized discrete equations. At the end of the paper some valuable applications are pointed out.

  • 262.
    Hu, Shaolin
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS. Nanjing University of Science and Technology, China .
    Chen, R.
    Meinke, Karl
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Huajiang, O.
    Dynamic-measurement system modeling of spinning spacecraft attitude and their applications2007In: Chinese Space Science and Technology, ISSN 1000-758X, Vol. 27, no 4, p. 1-6+20Article in journal (Refereed)
    Abstract [en]

    The modeling analysis technique is one of the most important approaches in space-flight mission. Based on the dynamical analysis, the copling models of the attitudes with angle velocities were successfully decoupled into two series independently differential equations. And, these two series models were integrated into an extended dynamic-measurement system with joint relationship equations. This new integrated model could be widely used in attitude determination, attitude control and attitude monitoring of the spinning spacecraft. Based on this integrated model, a series of practical algorithms were described to estimate attitude as well as spinning angles velocities with high precision.

  • 263.
    Hu, Shaolin
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS. Nanjing University of Science and Technology, China .
    Meinke, Karl
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Chen, R.
    Fault-tolerant design of computer cyclic check and control system2007In: Proceedings of the 26th Chinese Control Conference, CCC 2007, 2007, p. 426-430Conference paper (Refereed)
    Abstract [en]

    Computer Cyclic Check is widely used in many different fields. Some limitations as well as bugs of classical algorithms in the computer cyclic check system are analyzed in detailed. In order to overcome these advantages, two series of new algorithms are set up in this paper, one of which is built for the computer cyclic check system with fixed reference value and the other for the computer cyclic check under operation steering with variant directive trajectory. Theoretical analysis and simulation result shows that these new algorithms are fault-tolerant and safe. These new algorithms can be widely used in engineering to improve safety of computer cyclic check system.

  • 264.
    Hu, Shaolin
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Meinke, Karl
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Chen, R. -S
    Fault-tolerant algorithm of signal reconstruction in computer controlled systems2006In: Xitong Fangzhen Xuebao / Journal of System Simulation, ISSN 1004-731X, Vol. 18, no SUPPL. 2, p. 841-843Article in journal (Refereed)
    Abstract [en]

    Signal reconstruction is an important step in communication between the computer controlled system and computer system. Based on the famous Shannon reconstructing theory, some classical algorithms (such as ZOH algorithm and 1-order reconstruction algorithm, etc.) were analyzed and some shortages of these algorithms were pointed out. And, a new practical 1-step fault-tolerant prediction algorithm was set up. In order to realize this fault-tolerant algorithm, the three-points-interpolation algorithm was combined into the reconstruction process. This new algorithm has the ability to overcome bad influence from outliers and has very simple computing complexity. So, this algorithm can be safely used in on-line control.

  • 265.
    Hu, Shaolin
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Meinke, Karl
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Chen, Rushan
    Huajiang, Ouyang
    Iterative estimators of parameters in linear models with partially variant coefficients2007In: International Journal of Applied Mathematics and Computer Sciences, ISSN 1307-6906, Vol. 17, no 2, p. 179-187Article in journal (Refereed)
    Abstract [en]

    A new kind of linear model with partially variant coefficients is proposed and a series of iterative algorithms are introduced and verified. The new generalized linear model includes the ordinary linear regression model as a special case. The iterative algorithms efficiently overcome some difficulties in computation with multidimensional inputs and incessantly appending parameters. An important application is described at the end of this article, which shows that this new model is reasonable and applicable in practical fields.

  • 266. Huang, Chien-Chung
    et al.
    Na Nongkai, Danupon
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Saranurak, Thatchaphol
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Distributed Exact Weighted All-Pairs Shortest Paths in (O)over-tilde(n(5/4)) Rounds2017In: 2017 IEEE 58th Annual Symposium on Foundations of Computer Science (FOCS), IEEE, 2017, p. 168-179Conference paper (Refereed)
    Abstract [en]

    We study computing all-pairs shortest paths (APSP) on distributed networks (the CONGEST model). The goal is for every node in the (weighted) network to know the distance from every other node using communication. The problem admits (1+ o(1))-approximation (O) over tilde (n)-time algorithms [2], [3], which are matched with (Omega) over tilde (n)-time lower bounds [3], [4], [5](1). No omega(n) lower bound or o(m) upper bound were known for exact computation. In this paper, we present an (O) over tilde (n(5/4))-time randomized (Las Vegas) algorithm for exact weighted APSP; this provides the first improvement over the naive O(m)-time algorithm when the network is not so sparse. Our result also holds for the case where edge weights are asymmetric (a. k. a. the directed case where communication is bidirectional). Our techniques also yield an (O) over tilde (n(3/4) k(1/2) + n)-time algorithm for the k-source shortest paths problem where we want every node to know distances from k sources; this improves Elkin's recent bound [6] when k = (omega) over tilde (n(1/4)). We achieve the above results by developing distributed algorithms on top of the classic scaling technique, which we believe is used for the first time for distributed shortest paths computation. One new algorithm which might be of an independent interest is for the reversed r-sink shortest paths problem, where we want every of r sinks to know its distances from all other nodes, given that every node already knows its distance to every sink. We show an (O) over tilde (n root r)-time algorithm for this problem. Another new algorithm is called short range extension, where we show that in (O) over tilde (n root h) time the knowledge about distances can be "extended" for additional h hops. For this, we use weight rounding to introduce small additive errors which can be later fixed. Remark: Independently from our result, Elkin recently observed in [6] that the same techniques from an earlier version of the same paper (https://arxiv.org/abs/1703.01939v1) led to an O(n(5/3) log(2/3) n)-time algorithm.

  • 267.
    Huang, Sangxia
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Approximation Resistance on Satisfiable Instances for Predicates Strictly Dominating Parity2012Report (Other academic)
    Abstract [en]

    In this paper, we study the approximability of Max CSP(P) where P is a Boolean predicate. We prove that assuming Khot’s d-to-1 Conjecture, if the set of accepting inputs of P strictly contains all inputs with even (or odd) parity, then it is NP-hard to approximate MaxCSP(P) better than the simple random assignment algorithm even on satisfiable instances.This is a generalization of a work by O’Donnell and Wu which proved that it is NP-hard to approximate satisfiable instances of Max CSP(NTW) beyond 5/8 + epsilon for any epsilon > 0 based on Khot’s d-to-1 Conjecture, where NTW is the “Not Two” predicate of size 3.

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    tr12-040
  • 268.
    Huang, Sangxia
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Approximation resistance on satisfiable instances for predicates with few accepting inputs2013In: Symposium on Theory of Computing Conference / [ed] Dan Boneh, Tim Roughgarden, Joan Feigenbaum, 2013, p. 457-466Conference paper (Refereed)
    Abstract [en]

     For every integer k≥ 3, we prove that there is a predicate P on k Boolean variables with 2O(k1/3) accepting assignments that is approximation resistant even on satisfiable instances. That is, given a satisfiable CSP instance with constraint P, we cannot achieve better approximation ratio than simply picking random assignments. This improves the best previously known result by Hastad and Khot where the predicate has 2 O(k1/2) accepting assignments.

    Our construction is inspired by several recent developments. One is the idea of using direct sums to improve soundness of PCPs, developed by Chan [5]. We also use techniques from Wenner [32] to construct PCPs with perfect completeness without relying on the d-to-1 Conjecture.

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    stoc13
  • 269.
    Huang, Sangxia
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Hardness of Constraint Satisfaction and Hypergraph Coloring: Constructions of Probabilistically Checkable Proofs with Perfect Completeness2015Doctoral thesis, monograph (Other academic)
    Abstract [en]

    A Probabilistically Checkable Proof (PCP) of a mathematical statement is a proof written in a special manner that allows for efficient probabilistic verification. The celebrated PCP Theorem states that for every family of statements in NP, there is a probabilistic verification procedure that checks the validity of a PCP proof by reading only 3 bits from it. This landmark theorem, and the works leading up to it, laid the foundation for many subsequent works in computational complexity theory, the most prominent among them being the study of inapproximability of combinatorial optimization problems.

    This thesis focuses on a broad class of combinatorial optimization problems called Constraint Satisfaction Problems (CSPs). In an instance of a CSP problem of arity k, we are given a set of variables taking values from some finite domain, and a set of constraints each involving a subset of at most k variables. The goal is to find an assignment that simultaneously satisfies as many constraints as possible. An alternative formulation of the goal that is commonly used is Gap-CSP, where the goal is to decide whether a CSP instance is satisfiable or far from satisfiable, where the exact meaning of being far from satisfiable varies depending on the problems.We first study Boolean CSPs, where the domain of the variables is {0,1}. The main question we study is the hardness of distinguishing satisfiable Boolean CSP instances from those for which no assignment satisfies more than some epsilon fraction of the constraints. Intuitively, as the arity increases, the CSP gets more complex and thus the hardness parameter epsilon should decrease. We show that for Boolean CSPs of arity k, it is NP-hard to distinguish satisfiable instances from those that are at most 2^{~O(k^{1/3})}/2^k-satisfiable.

    We also study coloring of graphs and hypergraphs. Given a graph or a hypergraph, a coloring is an assignment of colors to vertices, such that all edges or hyperedges are non-monochromatic. The gap problem is to distinguish instances that are colorable with a small number of colors, from those that require a large number of colors. For graphs, we prove that there exists a constant K_0>0, such that for any K >= K_0, it is NP-hard to distinguish K-colorable graphs from those that require 2^{Omega(K^{1/3})} colors. For hypergraphs, we prove that it is quasi-NP-hard to distinguish 2-colorable 8-uniform hypergraphs of size N from those that require 2^{(log N)^{1/4-o(1)}} colors.

    In terms of techniques, all these results are based on constructions of PCPs with perfect completeness, that is, PCPs where the probabilistic proof verification procedure always accepts a correct proof. Not only is this a very natural property for proofs, but it can also be an essential requirement in many applications. It has always been particularly challenging to construct PCPs with perfect completeness for NP statements due to limitations in techniques. Our improved hardness results build on and extend many of the current approaches. Our Boolean CSP result and GraphColoring result were proved by adapting the Direct Sum of PCPs idea by Siu On Chan to the perfect completeness setting. Our proof for hypergraph coloring hardness improves and simplifies the recent work by Khot and Saket, in which they proposed the notion of superposition complexity of CSPs.

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    Thesis
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    Errata
  • 270.
    Huang, Sangxia
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Improved Hardness of Approximating Chromatic Number2013In: Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques: 16th International Workshop, APPROX 2013, and 17th International Workshop, RANDOM 2013, Berkeley, CA, USA, August 21-23, 2013. Proceedings / [ed] Prasad Raghavendra, Sofya Raskhodnikova, Klaus Jansen, José D. P. Rolim, Springer, 2013, p. 233-243Conference paper (Refereed)
    Abstract [en]

    We prove that for sufficiently large K, it is NP-hard to color K-colorable graphs with less than 2Ω(K 1/3) colors. This improves the previous result of K versus K1/25 log K in Khot [1].

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  • 271.
    Huang, Sangxia
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Lu, Pinyan
    A Dichotomy for Real Weighted Holant Problems2012In: 2012 IEEE 27th Annual Conference On Computational Complexity (CCC), IEEE , 2012, p. 96-106Conference paper (Refereed)
    Abstract [en]

    Holant is a framework of counting characterized by local constraints. It is closely related to other well-studied frameworks such as #CSP and Graph Homomorphism. An effective dichotomy for such frameworks can immediately settle the complexity of all combinatorial problems expressible in that framework. Both #CSP and Graph Homomorphism can be viewed as sub-families of Holant with the additional assumption that the equality constraints are always available. Other subfamilies of Holant such as Holant* and Holant(c) problems, in which we assume some specific sets of constraints to be freely available, were also studied. The Holant framework becomes more expressive and contains more interesting tractable cases with less or no freely available constraint functions, while, on the other hand, it also becomes more challenging to obtain a complete characterization of its time complexity. Recently, complexity dichotomy for a variety of sub-families of Holant such as #CSP, Graph Homomorphism, Holant* and Holant(c) were proved. The dichotomy for the general Holant framework, which is the most desirable, still remains open. In this paper, we prove a dichotomy for the general Holant framework where all the constraints are real symmetric functions. This setting already captures most of the interesting combinatorial problems defined by local constraints, such as (perfect) matching, independent set, vertex cover and so on. This is the first time a dichotomy is obtained for general Holant Problems without any auxiliary functions. One benefit of working with Holant framework is some powerful new reduction techniques such as Holographic reduction. Along the proof of our dichotomy, we introduce a new reduction technique, namely realizing a constraint function by approximating it. This new technique is employed in our proof in a situation where it seems that all previous reduction techniques fail, thus this new idea of reduction might also be of independent interest. Besides proving dichotomy and developing new technique, we also obtained some interesting by-products. We prove a dichotomy for #CSP restricting to instances where each variable appears a multiple of d times for any d. We also prove that counting the number of Eulerian-Orientations on 2k-regular graphs is #P-hard for any k >= 2.

  • 272. Huisman, Marieke
    et al.
    Aktug, Irem
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Gurov, Dilian
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Program Models for Compositional Verification2008In: FORMAL METHODS AND SOFTWARE ENGINEERING, PROCEEDINGS, Berlin: Springer , 2008, p. 147-166Conference paper (Refereed)
    Abstract [en]

    Compositional verification is crucial for guaranteeing the security of systems where new components can be loaded dynamically. In earlier work, we developed a compositional verification principle for control-flow properties of sequential control flow graphs with procedures. This paper discusses how the principle can be generalised to richer program models. We first present a generic program model, of which the original program model is an instantiation, and explicate under what conditions the compositional verification principle applies. We then present two other example instantiations of the generic model: with exceptional and with multi-threaded control flow, and show that for these particular instantiations the conditions hold. The program models we present are specifically tailored to our compositional verification principle, however, they are sufficiently intuitive and standard to be useful on their own. Tool support and practical application of the method are discussed.

  • 273.
    Huisman, Marieke
    et al.
    INRIA Sophia Antipolis, France.
    Gurov, Dilian
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Composing Modal Properties of Programs with Procedures2009In: Electronical Notes in Theoretical Computer Science, ISSN 1571-0661, E-ISSN 1571-0661, Vol. 203, no 7, p. 87-101Article in journal (Refereed)
    Abstract [en]

    In component based software design, formal reasoning about programs has to be compositional, allowing global, program-wide properties to be inferred from the properties of its components. The present paper addresses the problem of compositional verification of behavioural control flow properties of sequential programs with procedures, expressed in a modal logic. We use as a starting point a maximal model based method previously developed by the authors, which assumes the local properties to be structural (rather than behavioural). To handle local behavioural properties, we propose the combination of the above method with a translation from behavioural properties to sets of structural ones. The present paper presents a direct solution for the logic, and prepares the ground for a translation for the considerably more expressive logic obtained by adding greatest fixed-point recursion.

  • 274.
    Huisman, Marieke
    et al.
    Univ Twente, Enschede, Netherlands.
    Gurov, Dilian
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    CVPP: A Tool Set for Compositional Verification of Control-Flow Safety Properties2011In: Formal verification of oblect-oriented software / [ed] Beckert, B; Marche, C, 2011, Vol. 6528, p. 107-121Conference paper (Refereed)
    Abstract [en]

    This paper describes CVPP, a tool set for compositional verification of control-flow safety properties for programs with procedures. The compositional verification principle that underlies CVPP is based on maximal models constructed from component specifications. Maximal models replace the actual components when verifying the whole program, either for the purposes of modularity of verification or due to unavailability of the component implementations at verification time. A characteristic feature of the principle and the tool set is the distinction between program structure and behaviour. While behavioural properties are more abstract and convenient for specification purposes, structural ones are easier to manipulate, in particular when it comes to verification or the construction of maximal models. Therefore, CVPP also contains the means to characterise a given behavioural formula by a set of structural formulae. The paper presents the underlying framework for compositional verification and the components of the tool set. Several verification scenarios are described, as well as wrapper tools that support the automatic execution of such scenarios, providing appropriate pre- and post-processing to interface smoothly with the user and to encapsulate the inner workings of the tool set.

  • 275. Huynh, Trinh
    et al.
    Nordström, Jakob
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On the virtue of succinct proofs: amplifying communication complexity hardness to time-space trade-offs in proof complexity2012In: Proceedings of the Annual ACM Symposium on Theory of Computing, 2012, p. 233-247Conference paper (Refereed)
    Abstract [en]

    An active line of research in proof complexity over the last decade has been the study of proof space and trade-offs between size and space. Such questions were originally motivated by practical SAT solving, but have also led to the development of new theoretical concepts in proof complexity of intrinsic interest and to results establishing nontrivial relations between space and other proof complexity measures. By now, the resolution proof system is fairly well understood in this regard, as witnessed by a sequence of papers leading up to [Ben-Sasson and Nordstrom 2008, 2011] and [Beame, Beck, and Impagliazzo 2012]. However, for other relevant proof systems in the context of SAT solving, such as polynomial calculus (PC) and cutting planes (CP), very little has been known. Inspired by [BN08, BN11], we consider CNF encodings of so-called pebble games played on graphs and the approach of making such pebbling formulas harder by simple syntactic modifications. We use this paradigm of hardness amplification to make progress on the relatively longstanding open question of proving time-space trade-offs for PC and CP. Namely, we exhibit a family of modified pebbling formulas {F n} n such that: • The formulas F n have size Θ(n) and width O(1). • They have proofs in length O(n) in resolution, which generalize to both PC and CP. • Any refutation in CP or PCR (a generalization of PC) in length L and space s must satisfy s log L > 4√n. A crucial technical ingredient in these results is a new two-player communication complexity lower bound for composed search problems in terms of block sensitivity, a contribution that we believe to be of independent interest.

  • 276.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    An Average-case Depth Hierarchy Theorem for Higher Depths2016In: 2016 IEEE 57th Annual IEEE Symposium on Foundations of Computer Science (FOCS), IEEE Computer Society, 2016, Vol. 2016, p. 79-88Conference paper (Refereed)
    Abstract [en]

    We extend the recent hierarchy results of Ross-man, Servedio and Tan [1] to address circuits of almost logarithmic depth. Our proof uses the same basic approach as [1] but a number of small differences enables us to obtain a stronger result by a significantly shorter proof.

  • 277.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Every 2-CSP Allows Nontrivial Approximation2005In: Proceedings of the 37th Annual ACM Symposium on Theory of Computing, 2005, p. 740-746Conference paper (Refereed)
    Abstract [en]

    We use semidefinite programming to prove that any constraint satisfaction problem in two variables over any domain allows an efficient approximation algorithm that does provably better than picking a random assignment. To be more precise assume that each variable can take values in [d] and that each constraint rejects t out of the d2 possible input pairs. Then, for some universal constant c, we can, in probabilistic polynomial time, find an assignment whose objective value is, on expectation, within a factor (1- t/d2(1- c/d2 log d)) of optimal.

  • 278.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    EVERY 2-CSP ALLOWS NONTRIVIAL APPROXIMATION2008In: Computational Complexity, ISSN 1016-3328, E-ISSN 1420-8954, Vol. 17, no 4, p. 549-566Article in journal (Refereed)
    Abstract [en]

    We use semidefinite programming to prove that any constraint satisfaction problem in two variables over any domain allows an efficient approximation algorithm that does better than picking a random assignment. Specifically we consider the case when each variable can take values in [d] and that each constraint rejects t out of the d(2) possible input pairs. Then, for some universal constant c, we can, in probabilistic polynomial time, find an assignment whose objective value is, in expectation, within a factor 1 - t/d(2) + ct/d(4) log d of optimal, improving on the trivial bound of 1 - t/d(2).

  • 279.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On Nontrivial Approximation of CSPs2007Conference paper (Refereed)
    Abstract [en]

    Constraint satisfaction problems, more simply called CSPs are central in computer science, the most famous probably being Satisfiability, SAT, the basic NP-complete problem. In this talk we survey some results about the optimization version of CSPs where we want to satisfy as many constraints as possible. One very simple approach to a CSP is to give random values to the variables. It turns out that for some CSPs, one example being Max-3Sat, unless P=NP, there is no polynomial time algorithm that can achieve a an approximation ratio that is superior to what is obtained by this trivial strategy. Some other CSPs, Max-Cut being a prime example, do allow very interesting non-trivial approximation algorithms which do give an approximation ratio that is substantially better than that obtained by a random assignment. These results hint at a general classification problem of determining which CSPs do admit a polynomial time approximation algorithm that beats the random assignment by a constant factor. Positive results giving such algorithms tend to be based on semi-definite programming while the PCP theorem is the central tool for proving negative result. We describe many of the known results in the area and also discuss some of the open problems.

  • 280.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On small-depth Frege proofs for Tseitin for grids2017In: 2017 IEEE 58th Annual Symposium on Foundations of Computer Science (FOCS), IEEE, 2017, p. 97-108Conference paper (Refereed)
    Abstract [en]

    We prove a lower bound on the size of a small depth Frege refutation of the Tseitin contradiction on the grid. We conclude that polynomial size such refutations must use formulas of almost logarithmic depth.

  • 281.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On the approximation resistance of a random predicate2007In: Approximation, Randomization, and Combinatorial Optimization: Algorithms and Techniques / [ed] Charikar, M; Reingold, O; Jansen, K; Rolim, JDP, BERLIN: SPRINGER-VERLAG BERLIN , 2007, Vol. 4627, p. 149-163Conference paper (Other academic)
    Abstract [en]

    A predicate is approximation resistant if no probabilistic polynomial time approximation algorithm can do significantly better then the naive algorithm that picks an assignment uniformly at random. Assuming that the Unique Games Conjecture is true we prove that most Boolean predicates are approximation resistant.

  • 282.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On the correlation of parity and small-depth circuits2014In: SIAM journal on computing (Print), ISSN 0097-5397, E-ISSN 1095-7111, Vol. 43, no 5, p. 1699-1708Article in journal (Refereed)
    Abstract [en]

    We prove that the correlation of a depth-d unbounded fanin circuit of size S with parity of n variables is at most 2(-Omega(n/(log S)d-1)).

  • 283.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On the efficient approximability of constraint satisfaction problems2007In: London Mathematical Society Lecture Notes, ISSN 0076-0552, Vol. 346, p. 201-222Article in journal (Refereed)
    Abstract [en]

    We discuss some results about the efficient approximability of constraint satisfaction problems.  in particular we focus on the question on an efficient algorithm can perform significantly better than the algorithm that picks a solution uniformly at random.

  • 284.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On the np-hardness of max-not-22014In: SIAM journal on computing (Print), ISSN 0097-5397, E-ISSN 1095-7111, Vol. 43, no 1, p. 179-193Article in journal (Refereed)
    Abstract [en]

    We prove that, for any epsilon > 0, given a satisfiable instance of Max-NTW (Not-2), it is NP-hard to find an assignment that satisfies a fraction 5/8 + epsilon of the constraints. This, up to the existence of epsilon, matches the approximation ratio obtained by the trivial algorithm that just picks an assignment at random, and thus the result is tight. Said equivalently, the result proves that Max-NTW is approximation resistant on satisfiable instances, and this makes complete our understanding of arity three maximum constraint satisfaction problems with regards to approximation resistance.

  • 285.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    On the NP-hardness of Max-Not-22012In: Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques, Springer-Verlag , 2012, p. 170-181Conference paper (Refereed)
    Abstract [en]

    We prove that, for any ε > 0, it is NP-hard to, given a satisfiable instance of Max-NTW (Not-2), find an assignment that satisfies a fraction 5/8 + ε of the constraints. This, up to the existence of ε, matches the approximation ratio obtained by the trivial algorithm that just picks an assignment at random and thus the result is tight. Said equivalently the result proves that Max-NTW is approximation resistant on satisfiable instances and this makes our understanding of arity three Max-CSPs with regards to approximation resistance complete.

  • 286.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Satisfying degree-d equations of GF[2]2011In: Proceedings of the 14th international workshop and 15th international conference on Approximation, randomization, and combinatorial optimization:: algorithms and techniques, 2011, p. 242-253Conference paper (Refereed)
    Abstract [en]

    We study the problem where we are given a system of polynomial equations defined by multivariate polynomials over GF[2] of fixed constant degree d > 1 and the aim is to satisfy the maximal number of equations. A random assignment approximates this problem within a factor 2-d and we prove that for any ε > 0, it is NP-hard to obtain a ratio 2-d + ε. When considering instances that are perfectly satisfiable we give a probabilistic polynomial time algorithm that, with high probability, satisfies a fraction 21-d - 21-2d and we prove that it is NP-hard to do better by an arbitrarily small constant. The hardness results are proved in the form of inapproximability results of Max-CSPs where the predicate in question has the desired form and we give some immediate results on approximation resistance of some predicates.

  • 287.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Satisfying Degree-d Equations of GF(2)n2011Conference paper (Refereed)
    Abstract [en]

    We study the problem where we are given a system of polynomial equations defined by multivariate polynomials over GF[2] of fixed constant degree d > 1 and the aim is to satisfy the maximal number of equations. A random assignment approximates this problem within a factor 2−d and we prove that for any ε > 0, it is NP-hard to obtain a ratio 2−d+ε. When considering instances that are perfectly satisfiable we give a probabilistic polynomial time algorithm that, with high probability, satisfies a fraction 21−d − 21−2d and we prove that it is NP-hard to do better by an arbitrarily small constant. The hardness results are proved in the form of inapproximability results of Max-CSPs where the predicate in question has the desired form and we give some immediate results on approximation resistance of some predicates.

  • 288.
    Håstad, Johan
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Special issue "conference on computational complexity 2009" guest editor's foreword2010In: Computational Complexity, ISSN 1016-3328, E-ISSN 1420-8954, Vol. 19, no 2, p. 151-152Article in journal (Refereed)
  • 289.
    Håstad, Johan
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Huang, Sangxia
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Manokaran, R.
    O’Donnell, R.
    Wright, J.
    Improved NP-inapproximability for 2-variable linear equations2015In: Leibniz International Proceedings in Informatics, LIPIcs, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH , 2015, Vol. 40, p. 341-360Conference paper (Refereed)
    Abstract [en]

    An instance of the 2-Lin(2) problem is a system of equations of the form "xi + xj = b (mod 2)". Given such a system in which it’s possible to satisfy all but an C ε fraction of the equations, we show it is NP-hard to satisfy all but a Cε fraction of the equations, for any C < 11/8 = 1.375 (and any 0 < ε ≤ 1/8). The previous best result, standing for over 15 years, had 5/4 in place of 11/8. Our result provides the best known NP-hardness even for the Unique-Games problem, and it also holds for the special case of Max-Cut. The precise factor 11 8 is unlikely to be best possible; we also give a conjecture concerning analysis of Boolean functions which, if true, would yield a larger hardness factor of 3/2. Our proof is by a modified gadget reduction from a pairwise-independent predicate. We also show an inherent limitation to this type of gadget reduction. In particular, any such reduction can never establish a hardness factor C greater than 2.54. Previously, no such limitation on gadget reductions was known.

  • 290.
    Håstad, Johan
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Khot, Subhash
    Query efficient PCPs with perfect completeness2005In: Theory of Computing, E-ISSN 1557-2862, Vol. 1, p. 119-149Article in journal (Refereed)
    Abstract [en]

    For every integer k >0, and an arbitrarily small constante> 0, we present a PCP characterization of NP where the verifier uses logarithmic randomness, non-adaptively queries 4 k +k2 bits in the proof, accepts a correct proof with probability 1, i. e., it has perfect completeness, and accepts any supposed proof of a false statement with probability at most 2 −k2 +e. In particular, the verifier achieves optimal amortized query complexity of 1 +dfor arbitrarily small constantd> 0. Such a characterization was already proved by Samorodnitsky and Trevisan (STOC 2000), but their verifier loses perfect completeness and their proof makes an essential use of this feature. By using an adaptive verifier, we can decrease the number of query bits to 2 k +k2 , equal to the number obtained by Samorodnitsky and Trevisan. Finally we extend some of the results to PCPs over non-Boolean alphabets.

  • 291.
    Håstad, Johan
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Manokaran, Rajsekar
    IIT Madras, Madras, Tamil Nadu, India.;Indian Inst Technol, Madras, Tamil Nadu, India..
    On the Hardness of Approximating Balanced Homogeneous 3-Lin2017In: Theory of Computing, E-ISSN 1557-2862, Vol. 13, article id UNSP 10Article in journal (Refereed)
    Abstract [en]

    We consider systems of homogeneous linear equations modulo 2 with three variables in each equation and study balanced assignments as solutions to such equations. We prove that it is hard to distinguish systems where there is a balanced assignment that satisfies a fraction 1-epsilon of the equations from systems where the best balanced assignment satisfies a fraction 1/2 + epsilon of the equations assuming that NP is not contained in quasipolynomial time. This improves on a similar result by Holmerin and Khot who relied on the assumption that NP is not contained in subexponential time. The key for the improvement is to replace long codes used by Holmerin and Khot by the low-degree long code.

  • 292.
    Håstad, Johan
    et al.
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Pass, Rafael
    Wikström, Douglas
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Pietrzak, Krzysztof
    An Efficient Parallel Repetition Theorem2010In: THEORY OF CRYPTOGRAPHY, PROCEEDINGS / [ed] Micciancio D, 2010, Vol. 5978, p. 1-18Conference paper (Refereed)
    Abstract [en]

    We present a general parallel-repetition theorem with an efficient reduction. As a corollary of this theorem we establish that parallel repetition reduces the soundness error at an exponential rate in any public-coin argument, and more generally, any argument where the verifier's messages, but not necessarily its decision to accept or reject, can be efficiently simulated with noticeable probability.

  • 293.
    Håstad, Johan
    et al.
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Wigderson, Avi
    The randomized communicatin complexity of set disjointness2007In: Theory of Computing, E-ISSN 1557-2862, Vol. 3, p. 211-219Article in journal (Refereed)
    Abstract [en]

    We study the communication complexity of the disjointness function, in which each of two players holds a k-subset of a universe of size n and the goal is to determine whether the sets are disjoint. In the model of a common random string we prove that O(k) communication bits are sufficient, regardless of n. In the model of private random coins O(k + log log n) bits suffice. Both results are asymptotically tight.

  • 294. Höök, Kristina
    et al.
    Karlgren, Jussi
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Some Principles for Route Descriptions Derived from Human Advisers1991In: Proceedings of the 13th Annual Meeting of the Cognitive Science Society, 1991Conference paper (Refereed)
  • 295. Höök, Kristina
    et al.
    Karlgren, Jussi
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Waern, Annika
    Inferring complex plans1993In: 1st International Workshop on Intelligent User Interfaces, 1993Conference paper (Refereed)
    Abstract [en]

    We examine the need for plan inference in intelligent help mechanisms. We argue that previous approaches have drawbacks that need to be overcome to make plan inference useful. Firstly, plans have to be inferred - not extracted from the users? help requests. Secondly, the plans inferred must be more than a single goal or solitary user command.

  • 296. Höök, Kristina
    et al.
    Karlgren, Jussi
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Waern, Annika
    Dahlbäck, Nils
    Jansson, Carl Gustaf
    Karlgren, Klas
    Lemaire, Benoit
    A glass box approach to adaptive hypermedia1996In: User Modeling and User-Adapted Interaction, Vol. 6, p. 157-184Article in journal (Refereed)
    Abstract [en]

    Utilising adaptive interface techniques in the design of systems introduces certain risks. An adaptive interface is not static, but will actively adapt to the perceived needs of the user. Unless carefully designed, these changes may lead to an unpredictable, obscure and uncontrollable interface. Therefore the design of adaptive interfaces must ensure that users can inspect the adaptivity mechanisms, and control their results. One way to do this is to rely on the user’s understanding of the application and the domain, and relate the adaptivity mechanisms to domain-specific concepts. We present an example of an adaptive hypertext help system POP, which is being built according to these principles, and discuss the design considerations and empirical findings that lead to this design.

  • 297. Janarthanam, S.
    et al.
    Lemon, O.
    Liu, X.
    Bartie, P.
    Mackaness, W.
    Dalmas, T.
    Götze, Jana
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Conversational Natural Language Interaction for Place-related Knowledge Acquisition2012In: Place-related Knowledge Acquisition Research Workshop (PKAR), Spatial Cognition Conference, 2012, p. 33-38Conference paper (Refereed)
    Abstract [en]

    We focus on the problems of using Natural Language interaction to support pedestrians in their place-related knowledge acquisition. Our case study for this discussion is a smartphone-based Natural Language interface that allows users to acquire spatial and cultural knowledge of a city. The framework consists of a spoken dialogue-based information system and a smartphone client. The system is novel in combining geographic information system (GIS) modules such as a visibility engine with a question-answering (QA) system. Users can use the smartphone client to engage in a variety of interleaved conversations such as navigating from A to B, using the QA functionality to learn more about points of interest (PoI) nearby, and searching for amenities and tourist attractions. This system explores a variety of research questions involving Natural Language interaction for acquisition of knowledge about space and place.

  • 298. Janarthanam, S.
    et al.
    Lemon, O.
    Liu, X.
    Bartie, P.
    Mackaness, W.
    Dalmas, T.
    Götze, Jana
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Integrating location, visibility, and Question-Answering in a spoken dialogue system for pedestrian city exploration2012In: Proceedings of SemDial 2012 (SeineDial): The 16th Workshop on the Semantics and Pragmatics of Dialogue / [ed] Sarah Brown-Schmidt, Jonathan Ginzburg, Staffan Larsson, 2012, p. 157-158Conference paper (Refereed)
    Abstract [en]

    We demonstrate a spoken dialogue-based information system for pedestrians. The system is novel in combining geographic information system (GIS) modules such as a visibility engine with a question-answering (QA) system,integrated within a dialogue system architecture. Users of the demonstration system can use a web-based version (simulating pedestrian movement using StreetView) to engage in a variety of interleaved navigation and QA conversations.

  • 299. Janarthanam, S.
    et al.
    Lemon, O.
    Liu, X.
    Bartie, P.
    Mackaness, W.
    Dalmas, T.
    Götze, Jana
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Integrating location, visibility, and Question-Answering in a spoken dialogue system for pedestrian city exploration2012In: Proceedings of the 13th Annual Meeting of the Special Interest Group on Discourse and Dialogue (SIGDIAL), 2012, p. 134-136Conference paper (Refereed)
    Abstract [en]

    We demonstrate a spoken dialogue-based information system for pedestrians. The system is novel in combining geographic information system (GIS) modules such as a visibility engine with a question-answering (QA) system, integrated within a dialogue system architecture. Users of the demonstration system can use a web-based version (simulating pedestrian movement using StreetView) to engage in a variety of interleaved conversations such as navigating from A to B, using the QA functionality to learn more about points of interest (PoI) nearby, and searching for amenities and tourist attractions. This system explores a variety of research questions involving the integration of multiple information sources within conversational interaction.

  • 300. Jansen, K.
    et al.
    Prädel, L.
    Schwarz, U. M.
    Svensson, Ola
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Faster approximation algorithms for scheduling with fixed jobs2011In: Conferences in Research and Practice in Information Technology Series, 2011, p. 3-9Conference paper (Refereed)
    Abstract [en]

    We study the problem of scheduling jobs on identical parallel machines without preemption. In the considered setting, some of the jobs are already assigned machines and starting times, for example due to external constraints not explicitly modelled. The objective is to assign the rest of the jobs in order to minimize the makespan. It is known that this problem cannot be approximated better than within a factor of 3/2 unless P = NP. An algorithm that achieves 3/2 + ε for any ε > 0 was presented by Diedrich and Jansen [DJ09], but its running time is doubly exponential in 1/ε. We present an improved algorithm with approximation ratio 3/2 and polynomial running time. We also give matching results for the related problem of scheduling with reservations. The new algorithm is both faster and conceptually simpler than the previously known algorithms.

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