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  • 1. AAl Abdulsalam, Abdulrahman
    et al.
    Velupillai, Sumithra
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. King's College, London.
    Meystre, Stephane
    UtahBMI at SemEval-2016 Task 12: Extracting Temporal Information from Clinical Text2016In: Proceedings of the 10th International Workshop on Semantic Evaluation (SemEval-2016), Association for Computational Linguistics , 2016, p. 1256-1262Conference paper (Refereed)
    Abstract [en]

    The 2016 Clinical TempEval continued the 2015 shared task on temporal information extraction with a new evaluation test set. Our team, UtahBMI, participated in all subtasks using machine learning approaches with ClearTK (LIBLINEAR), CRF++ and CRFsuite packages. Our experiments show that CRF-based classifiers yield, in general, higher recall for multi-word spans, while SVM-based classifiers are better at predicting correct attributes of TIMEX3. In addition, we show that an ensemble-based approach for TIMEX3 could yield improved results. Our team achieved competitive results in each subtask with an F1 75.4% for TIMEX3, F1 89.2% for EVENT, F1 84.4% for event relations with document time (DocTimeRel), and F1 51.1% for narrative container (CONTAINS) relations.

  • 2.
    Adriaens, Florian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. HIIT, University of Helsinki Helsinki, Finland.
    Apers, Simon
    Université de Paris, CNRS, IRIF Paris, France.
    Testing Cluster Properties of Signed Graphs2023In: ACM Web Conference 2023: Proceedings of the World Wide Web Conference, WWW 2023, Association for Computing Machinery (ACM) , 2023, p. 49-59Conference paper (Refereed)
    Abstract [en]

    This work initiates the study of property testing in signed graphs, where every edge has either a positive or a negative sign. We show that there exist sublinear query and time algorithms for testing three key properties of signed graphs: balance (or 2-clusterability), clusterability and signed triangle freeness. We consider both the dense graph model, where one queries the adjacency matrix entries of a signed graph, and the bounded-degree model, where one queries for the neighbors of a node and the sign of the connecting edge. Our algorithms use a variety of tools from unsigned graph property testing, as well as reductions from one setting to the other. Our main technical contribution is a sublinear algorithm for testing clusterability in the bounded-degree model. This contrasts with the property of k-clusterability in unsigned graphs, which is not testable with a sublinear number of queries in the bounded-degree model. We experimentally evaluate the complexity and usefulness of several of our testers on real-life and synthetic datasets.

  • 3.
    Adriaens, Florian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Diameter Minimization by Shortcutting with Degree Constraints2022In: 2022 IEEE INTERNATIONAL CONFERENCE ON DATA MINING (ICDM) / [ed] Zhu, X Ranka, S Thai, MT Washio, T Wu, X, Institute of Electrical and Electronics Engineers (IEEE) , 2022, p. 843-848Conference paper (Refereed)
    Abstract [en]

    We consider the problem of adding a fixed number of new edges to an undirected graph in order to minimize the diameter of the augmented graph, and under the constraint that the number of edges added for each vertex is bounded by an integer. The problem is motivated by network-design applications, where we want to minimize the worst case communication in the network without excessively increasing the degree of any single vertex, so as to avoid additional overload. We present three algorithms for this task, each with their own merits. The special case of a matching augmentation -when every vertex can be incident to at most one new edge- is of particular interest, for which we show an inapproximability result, and provide bounds on the smallest achievable diameter when these edges are added to a path. Finally, we empirically evaluate and compare our algorithms on several real-life networks of varying types.

  • 4.
    Adriaens, Florian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Mara, Alexandru
    IDLab, Ghent University, Belgium.
    Lijffijt, Jefrey
    IDLab, Ghent University, Belgium.
    De Bie, Tijl
    IDLab, Ghent University, Belgium.
    Block-approximated exponential random graphs2020In: Proceedings - 2020 IEEE 7th International Conference on Data Science and Advanced Analytics, DSAA 2020, Institute of Electrical and Electronics Engineers Inc. , 2020, p. 70-80Conference paper (Refereed)
    Abstract [en]

    An important challenge in the field of exponential random graphs (ERGs) is the fitting of non-trivial ERGs on large graphs. By utilizing fast matrix block-approximation techniques, we propose an approximative framework to such non-trivial ERGs that result in dyadic independence (i.e., edge independent) distributions, while being able to meaningfully model local information of the graph (e.g., degrees) as well as global information (e.g., clustering coefficient, assortativity, etc.) if desired. This allows one to efficiently generate random networks with similar properties as an observed network, and the models can be used for several downstream tasks such as link prediction. Our methods are scalable to sparse graphs consisting of millions of nodes.Empirical evaluation demonstrates competitiveness in terms of both speed and accuracy with state-of-the-art methods - which are typically based on embedding the graph into some low-dimensional space - for link prediction, showcasing the potential of a more direct and interpretable probablistic model for this task.

  • 5.
    Adriaens, Florian
    et al.
    University of Helsinki, Helsinki, Finland.
    Wang, Hongliang
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Minimizing hitting time between disparate groups with shortcut edges2023In: KDD 2023: Proceedings of the 29th ACM SIGKDD Conference on Knowledge Discovery and Data Mining, Association for Computing Machinery (ACM) , 2023, p. 1-10Conference paper (Refereed)
    Abstract [en]

    Structural bias or segregation of networks refers to situations where two or more disparate groups are present in the network, so that the groups are highly connected internally, but loosely connected to each other. Examples include polarized communities in social networks, antagonistic content in video-sharing or news-feed platforms, etc. In many cases it is of interest to increase the connectivity of disparate groups so as to, e.g., minimize social friction, or expose individuals to diverse viewpoints. A commonly-used mechanism for increasing the network connectivity is to add edge shortcuts between pairs of nodes. In many applications of interest, edge shortcuts typically translate to recommendations, e.g., what video to watch, or what news article to read next. The problem of reducing structural bias or segregation via edge shortcuts has recently been studied in the literature, and random walks have been an essential tool for modeling navigation and connectivity in the underlying networks. Existing methods, however, either do not offer approximation guarantees, or engineer the objective so that it satisfies certain desirable properties that simplify the optimization task. In this paper we address the problem of adding a given number of shortcut edges in the network so as to directly minimize the average hitting time and the maximum hitting time between two disparate groups. The objectives we study are more natural than objectives considered earlier in the literature (e.g., maximizing hitting-time reduction) and the optimization task is significantly more challenging. Our algorithm for minimizing average hitting time is a greedy bicriteria that relies on supermodularity. In contrast, maximum hitting time is not supermodular. Despite, we develop an approximation algorithm for that objective as well, by leveraging connections with average hitting time and the asymmetric k-center problem.

  • 6. Agarwal, D.
    et al.
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Simperl, E.
    Foreword from the Programme Chairs2022In: 31st ACM World Wide Web Conference, WWW 2022, Association for Computing Machinery, Inc , 2022Conference paper (Refereed)
  • 7.
    Ahmadian, Amir M.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Balliu, Musard
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Dynamic Policies Revisited2022In: Proceedings - 7th IEEE European Symposium on Security and Privacy, Euro S and P 2022, Institute of Electrical and Electronics Engineers (IEEE), 2022, p. 448-466Conference paper (Refereed)
    Abstract [en]

    Information flow control and dynamic policies is a difficult relationship yet to be fully understood. While dynamic policies are a natural choice in many real-world applications that downgrade and upgrade the sensitivity of information, understanding the meaning of security in this setting is challenging. In this paper we revisit the knowledge-based security conditions to reinstate a simple and intuitive security condition for dynamic policies: A program is secure if at any point during the execution the attacker's knowledge is in accordance with the active security policy at that execution point. Our key observation is the new notion of policy consistency to prevent policy changes whenever an attacker is already in possession of the information that the new policy intends to protect. We use this notion to study a range of realistic attackers including the perfect recall attacker, bounded attackers, and forgetful attackers, and their relationship. Importantly, our new security condition provides a clean connection between the dynamic policy and the underlying attacker model independently of the specific use case. We illustrate this by considering the different facets of dynamic policies in our framework. On the verification side, we design and implement DynCoVer, a tool for checking dynamic information-flow policies for Java programs via symbolic execution and SMT solving. Our verification operates by first extracting a graph of program dependencies and then visiting the graph to check dynamic policies for a range of attackers. We evaluate the effectiveness and efficiency of DyncoVeron a benchmark of use cases from the literature and designed by ourselves, as well as the case study of a social network. The results show that DynCoVer can analyze small but intricate programs indicating that it can help verify security-critical parts of Java applications. We release Dyncover publicly to support open science and encourage researchers to explore the topic further.

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  • 8. Ahmadpanah, M. M.
    et al.
    Balliu, Musard
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Hedin, D.
    Olsson, L. E.
    Sabelfeld, A.
    Securing Node-RED Applications2021In: Protocols, Strands, and LogicEssays Dedicated to Joshua Guttman on the Occasion of his 66.66th Birthday, Springer Science and Business Media Deutschland GmbH , 2021, p. 1-21Conference paper (Refereed)
    Abstract [en]

    Trigger-Action Platforms (TAPs) play a vital role in fulfilling the promise of the Internet of Things (IoT) by seamlessly connecting otherwise unconnected devices and services. While enabling novel and exciting applications across a variety of services, security and privacy issues must be taken into consideration because TAPs essentially act as persons-in-the-middle between trigger and action services. The issue is further aggravated since the triggers and actions on TAPs are mostly provided by third parties extending the trust beyond the platform providers. Node-RED, an open-source JavaScript-driven TAP, provides the opportunity for users to effortlessly employ and link nodes via a graphical user interface. Being built upon Node.js, third-party developers can extend the platform’s functionality through publishing nodes and their wirings, known as flows. This paper proposes an essential model for Node-RED, suitable to reason about nodes and flows, be they benign, vulnerable, or malicious. We expand on attacks discovered in recent work, ranging from exfiltrating data from unsuspecting users to taking over the entire platform by misusing sensitive APIs within nodes. We present a formalization of a runtime monitoring framework for a core language that soundly and transparently enforces fine-grained allowlist policies at module-, API-, value-, and context-level. We introduce the monitoring framework for Node-RED that isolates nodes while permitting them to communicate via well-defined API calls complying with the policy specified for each node.

  • 9.
    Ahmadpanah, Mohammad M.
    et al.
    Chalmers.
    Hedin, Daniel
    Chalmers and Mälardalen University.
    Balliu, Musard
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Olsson, Lars Eric
    Chalmers.
    Sabelfeld, Andrei
    Chalmers.
    SandTrap: Securing JavaScript-driven Trigger-Action Platforms2021Conference paper (Refereed)
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  • 10.
    Ahmadpanah, Mohammad M.
    et al.
    Chalmers Univ Technol, Gothenburg, Sweden..
    Hedin, Daniel
    Chalmers Univ Technol, Gothenburg, Sweden.;Mälardalen Univ, Västerås, Sweden..
    Balliu, Musard
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Olsson, Lars Eric
    Chalmers Univ Technol, Gothenburg, Sweden..
    Sabelfeld, Andrei
    Chalmers Univ Technol, Gothenburg, Sweden..
    SandTrap: Securing JavaScript-driven Trigger-Action Platforms2021In: Proceedings Of The 30Th USENIX Security Symposium, USENIX ASSOC , 2021, p. 2899-2916Conference paper (Refereed)
    Abstract [en]

    Trigger-Action Platforms (TAPs) seamlessly connect a wide variety of otherwise unconnected devices and services, ranging from IoT devices to cloud services and social networks. TAPs raise critical security and privacy concerns because a TAP is effectively a "person-in-the-middle" between trigger and action services. Third-party code, routinely deployed as "apps" on TAPs, further exacerbates these concerns. This paper focuses on JavaScript-driven TAPs. We show that the popular IFTTT and Zapier platforms and an open-source alternative Node-RED are susceptible to attacks ranging from exfiltrating data from unsuspecting users to taking over the entire platform. We report on the changes by the platforms in response to our findings and present an empirical study to assess the implications for Node-RED. Motivated by the need for a secure yet flexible way to integrate third-party JavaScript apps, we propose SandTrap, a novel JavaScript monitor that securely combines the Node.js vm module with fully structural proxy-based two-sided membranes to enforce fine-grained access control policies. To aid developers, SandTrap includes a policy generation mechanism. We instantiate SandTrap to IFTTT, Zapier, and Node-RED and illustrate on a set of benchmarks how SandTrap enforces a variety of policies while incurring a tolerable runtime overhead.

  • 11.
    Ahrendt, Wolfgang
    et al.
    Chalmers University of Technology, Gothenburg, Sweden.
    Gurov, Dilian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Johansson, Moa
    Chalmers University of Technology, Gothenburg, Sweden.
    Rümmer, Philipp
    University of Regensburg, Regensburg, Germany; Uppsala University, Uppsala, Sweden.
    TriCo—Triple Co-piloting of Implementation, Specification and Tests2022In: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), Springer Nature , 2022, Vol. 13701 LNCS, p. 174-187Conference paper (Refereed)
    Abstract [en]

    This white paper presents the vision of a novel methodology for developing safety-critical software, which is inspired by late developments in learning based co-piloting of implementations. The methodology, called TriCo, integrates formal methods with learning based approaches to co-pilot the agile, simultaneous development of three artefacts: implementation, specification, and tests. Whenever the user changes any of these, a TriCo empowered IDE would suggest changes to the other two artefacts in such a way that the three are kept consistent. The user has the final word on whether the changes are accepted, rejected, or modified. In the latter case, consistency will be checked again and re-established. We discuss the emerging trends which put the community in a good position to realise this vision, describe the methodology and workflow, as well as challenges and possible solutions for the realisation of TriCo.

  • 12.
    Alshnakat, Anoud
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Gurov, Dilian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Lidström, Christian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Rümmer, P.
    Constraint-Based Contract Inference for Deductive Verification2020In: Deductive Software Verification: Future Perspectives, Springer Nature , 2020, p. 149-176Chapter in book (Refereed)
    Abstract [en]

    Assertion-based software model checking refers to techniques that take a program annotated with logical assertions and statically verify that the assertions hold whenever program execution is at the corresponding control point. While the associated annotation overhead is relatively low, these techniques are typically monolithic in that they explore the state space of the whole program at once, and may therefore scale poorly to large programs. Deductive software verification, on the other hand, refers to techniques that prove the correctness of a piece of software against a detailed specification of what it is supposed to accomplish or compute. The associated verification techniques are modular and scale well to large code bases, but incur an annotation overhead that is often very high, which is a real obstacle for deductive verification to be adopted in industry on a wider scale. In this paper we explore synergies between the two mentioned paradigms, and in particular, investigate how interpolation-based Horn solvers used for software model checking can be instrumented to infer missing procedure contracts for use in deductive verification, thus aiding the programmer in the code annotation process. We summarise the main developments in the area of automated contract inference, and present our own experiments with contract inference for C programs, based on solving Horn clauses. To drive the inference process, we put program assertions in the main function, and adapt our TriCera tool, a model checker based on the Horn solver Eldarica, to infer candidate contracts for all other functions. The contracts are output in the ANSI C Specification Language (ACSL) format, and are then validated with the Frama-C deductive verification tool for C programs.

  • 13.
    Alshnakat, Anoud
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Lundberg, Didrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. Saab AB, Järfälla, Sweden.
    Guanciale, Roberto
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Dam, Mads
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Palmskog, Karl
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    HOL4P4: Semantics for a Verified Data Plane2022In: EuroP4 2022: Proceedings of the 5th International Workshop on P4 in Europe, Part of CoNEXT 2022, Association for Computing Machinery (ACM) , 2022, p. 39-45Conference paper (Refereed)
    Abstract [en]

    We introduce a formal semantics of P4 for the HOL4 interactive theorem prover. We exploit properties of the language, like the absence of call by reference and the copy-in/copy-out mechanism, to define a heapless small-step semantics that is abstract enough to simplify verification, but that covers the main aspects of the language: interaction with the architecture via externs, table match, and parsers. Our formalization is written in the Ott metalanguage, which allows us to export definitions to multiple interactive theorem provers. The exported HOL4 semantics allows us to establish machine-checkable proofs regarding the semantics, properties of P4 programs, and soundness of analysis tools.

  • 14. Alturki, Musab A.
    et al.
    Chen, Jing
    Luchangco, Victor
    Moore, Brandon
    Palmskog, Karl
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Peña, Lucas
    Roşu, Grigore
    Towards a Verified Model of the Algorand Consensus Protocol in Coq2020In: Formal Methods. FM 2019 International Workshops / [ed] Sekerinski, Emil; Moreira, Nelma; Oliveira, José N.; Ratiu, Daniel; Guidotti, Riccardo; Farrell, Marie; Luckcuck, Matt; Marmsoler, Diego; Campos, José; Astarte, Troy; Gonnord, Laure; Cerone, Antonio; Couto, Luis; Dongol, Brijesh; Kutrib, Martin; Monteiro, Pedro; Delmas, David, Cham: Springer, 2020, p. 362-367Conference paper (Refereed)
    Abstract [en]

    The Algorand blockchain is a secure and decentralized public ledger based on pure proof of stake rather than proof of work. At its core it is a novel consensus protocol with exactly one block certified in each round: that is, the protocol guarantees that the blockchain does not fork. In this paper, we report on our effort to model and formally verify the Algorand consensus protocol in the Coq proof assistant. Similar to previous consensus protocol verification efforts, we model the protocol as a state transition system and reason over reachable global states. However, in contrast to previous work, our model explicitly incorporates timing issues (e.g., timeouts and network delays) and adversarial actions, reflecting a more realistic environment faced by a public blockchain.

  • 15.
    Amilon, Jesper
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Esen, Zafer
    Gurov, Dilian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Lidström, Christian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Rümmer, Philipp
    An Exercise in Mind Reading: Automatic Contract Inference for Frama-C2024In: Guide to Software Verification with Frama-C: Core Components, Usages, and Applications, Springer Nature, 2024Chapter in book (Other academic)
  • 16.
    Amilon, Jesper
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Esen, Zafer
    Uppsala University, Uppsala, Sweden.
    Gurov, Dilian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Lidström, Christian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Rümmer, Philipp
    Uppsala University, Uppsala, Sweden; University of Regensburg, Regensburg, Germany.
    Automatic Program Instrumentation for Automatic Verification2023In: Computer Aided Verification: 35th International Conference, CAV 2023, Proceedings, Springer Nature , 2023, p. 281-304Conference paper (Refereed)
    Abstract [en]

    In deductive verification and software model checking, dealing with certain specification language constructs can be problematic when the back-end solver is not sufficiently powerful or lacks the required theories. One way to deal with this is to transform, for verification purposes, the program to an equivalent one not using the problematic constructs, and to reason about its correctness instead. In this paper, we propose instrumentation as a unifying verification paradigm that subsumes various existing ad-hoc approaches, has a clear formal correctness criterion, can be applied automatically, and can transfer back witnesses and counterexamples. We illustrate our approach on the automated verification of programs that involve quantification and aggregation operations over arrays, such as the maximum value or sum of the elements in a given segment of the array, which are known to be difficult to reason about automatically. We implement our approach in the MonoCera tool, which is tailored to the verification of programs with aggregation, and evaluate it on example programs, including SV-COMP programs.

  • 17.
    Amilon, Jesper
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Lidström, Christian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Gurov, Dilian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Deductive Verification Based Abstraction for Software Model Checking2022In: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), Springer Nature , 2022, Vol. 13701 LNCS, p. 7-28Conference paper (Refereed)
    Abstract [en]

    The research community working on formal software verification has historically evolved into two main camps, grouped around two verification methods that are typically referred to as Deductive Verification and Model Checking. In this paper, we present an approach that applies deductive verification to formally justify abstract models for model checking in the TLA framework. We present a proof-of-concept tool chain for C programs, based on Frama-C for deductive verification and TLA+ for model checking. As a theoretical foundation, we summarise a previously developed abstract contract theory as a framework for combining these two methods. Since the contract theory adheres to the principles of contract based design, this justifies the use of the approach in a real-world system design setting. We evaluate our approach on two case studies: a simple C program simulating opening and closing of files, as well as a C program based on real software from the automotive industry.

  • 18. Anagnostopoulos, A.
    et al.
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Parotsidis, N.
    Collaborative procrastination2020In: Leibniz International Proceedings in Informatics, LIPIcs, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2020Conference paper (Refereed)
    Abstract [en]

    The problem of inconsistent planning in decision making, which leads to undesirable effects such as procrastination, has been studied in the behavioral-economics literature, and more recently in the context of computational behavioral models. Individuals, however, do not function in isolation, and successful projects most often rely on team work. Team performance does not depend only on the skills of the individual team members, but also on other collective factors, such as team spirit and cohesion. It is not an uncommon situation (for instance, experienced by the authors while working on this paper) that a hard-working individual has the capacity to give a good example to her team-mates and motivate them to work harder. In this paper we adopt the model of Kleinberg and Oren (EC'14) on time-inconsistent planning, and extend it to account for the influence of procrastination within the members of a team. Our first contribution is to model collaborative work so that the relative progress of the team members, with respect to their respective subtasks, motivates (or discourages) them to work harder. We compare the total cost of completing a team project when the team members communicate with each other about their progress, with the corresponding cost when they work in isolation. Our main result is a tight bound on the ratio of these two costs, under mild assumptions. We also show that communication can either increase or decrease the total cost. We also consider the problem of assigning subtasks to team members, with the objective of minimizing the negative effects of collaborative procrastination. We show that whereas a simple problem of forming teams of two members can be solved in polynomial time, the problem of assigning n tasks to n agents is NP-hard.

  • 19.
    Andersson, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Karlander, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Sandberg, Mattias
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Admission to master programmes: What are the indicators for successful study performance?2023In: Bidrag från den 9:e utvecklingskonferensen för Sveriges ingenjörsutbildningar / [ed] Joel Midemalm, Amir Vadiee, Elisabeth Uhlemann, Fredrik Georgsson, Gunilla Carlsson-Kvarnlöf, Jonas Månsson, Kristina Edström, Lennart Pettersson och Pedher Johansson, Västerås: Mälardalens universitet, 2023, p. 9-18Conference paper (Refereed)
    Abstract [en]

    Admission of applicants to higher education in a fair, reliable, transparent, and efficient way is a real challenge, especially if there are more eligible applicants than available places and if there are applicants from many different educational systems. Previous research on best practices for admission to master’s programmes identified the key question about an applicant’s potential for success in studies, but was not able to provide an answer about how to rate the merits of the applicants. In this study, indicators for study success are analysed by comparing the study performance of 228 students in master’s programmes with their merits at the time of admission. The null hypothesis was that the applicant’s average grade at the time of admission is the only indictor for study success. After testing for potential bias using almost 20 possible other indicators, the null hypothesis had to be rejected for four indicators (in order of importance): (i) university ranking, (ii) length of bachelor’s studies within subject, (iii) English language test and (iv) subject matching between bachelor’s and master’s education. Evaluation of quality of prior education is tricky and results from this study clearly indicate that students from higher ranked universities possess better knowledge and stronger skills for our master’s programmes. Work is ongoing to improve the merit rating model by involving more master’s programmes at KTH and analysing performance data from a larger number of students.

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    Master-admission
  • 20.
    Andreasson, Annika
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Human Centered Technology, Media Technology and Interaction Design, MID.
    Artman, Henrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Human Centered Technology, Media Technology and Interaction Design, MID. FOI Swedish Defence Research Agency, Stockholm, SE-164 90, Sweden.
    Brynielsson, Joel
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. FOI Swedish Defence Research Agency, Stockholm, SE-164 90, Sweden.
    Franke, Ulrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Human Centered Technology, Media Technology and Interaction Design, MID. RISE Research Institutes of Sweden, Kista, SE-164 29, Sweden.
    A Census of Swedish Public Sector Employee Communication on Cybersecurity during the COVID-19 Pandemic2021In: Proceedings of the International Conference on Cyber Situational Awareness, Data Analytics and Assessment, CyberSA 2021, Institute of Electrical and Electronics Engineers (IEEE), 2021, p. 1-8Conference paper (Refereed)
    Abstract [en]

    The COVID-19 pandemic has accelerated the digitalization of the Swedish public sector, and to ensure the success of this ongoing process cybersecurity plays an integral part. While Sweden has come far in digitalization, the maturity of cybersecurity work across entities covers a wide range. One way of improving cybersecurity is through communication, thereby enhancing employee cyber situation awareness. In this paper, we conduct a census of Swedish public sector employee communication on cybersecurity at the beginning of the COVID-19 pandemic using questionnaires. The study shows that public sector entities find the same sources of information useful for their cybersecurity work. We find that nearly two thirds of administrative authorities and almost three quarters of municipalities are not yet at the implemented cybersecurity level. We also find that 71 % of municipalities have less than one dedicated staff for cybersecurity.

  • 21. Andrienko, G.
    et al.
    Andrienko, N.
    Boldrini, C.
    Caldarelli, G.
    Cintia, P.
    Cresci, S.
    Facchini, A.
    Giannotti, F.
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Guidotti, R.
    Mathioudakis, M.
    Muntean, C. I.
    Pappalardo, L.
    Pedreschi, D.
    Pournaras, E.
    Pratesi, F.
    Tesconi, M.
    Trasarti, R.
    (So) Big Data and the transformation of the city2020In: International Journal of Data Science and Analytics, ISSN 2364-415XArticle in journal (Refereed)
    Abstract [en]

    The exponential increase in the availability of large-scale mobility data has fueled the vision of smart cities that will transform our lives. The truth is that we have just scratched the surface of the research challenges that should be tackled in order to make this vision a reality. Consequently, there is an increasing interest among different research communities (ranging from civil engineering to computer science) and industrial stakeholders in building knowledge discovery pipelines over such data sources. At the same time, this widespread data availability also raises privacy issues that must be considered by both industrial and academic stakeholders. In this paper, we provide a wide perspective on the role that big data have in reshaping cities. The paper covers the main aspects of urban data analytics, focusing on privacy issues, algorithms, applications and services, and georeferenced data from social media. In discussing these aspects, we leverage, as concrete examples and case studies of urban data science tools, the results obtained in the “City of Citizens” thematic area of the Horizon 2020 SoBigData initiative, which includes a virtual research environment with mobility datasets and urban analytics methods developed by several institutions around Europe. We conclude the paper outlining the main research challenges that urban data science has yet to address in order to help make the smart city vision a reality.

  • 22.
    Apers, Simon
    et al.
    CNRS, IRIF, Paris, France..
    Efron, Yuval
    Columbia Univ, New York, NY USA..
    Gawrychowski, Pawel
    Univ Wroclaw, Wroclaw, Poland..
    Lee, Troy
    Univ Technol Sydney, QSI, Sydney, NSW, Australia..
    Mukhopadhyay, Sagnik
    Univ Sheffield, Sheffield, S Yorkshire, England..
    Na Nongkai, Danupon
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. Max Planck Inst Informat, Saarbrucken, Germany.;Univ Copenhagen, Copenhagen, Denmark..
    Cut Query Algorithms with Star Contraction2022In: 2022 IEEE 63RD ANNUAL SYMPOSIUM ON FOUNDATIONS OF COMPUTER SCIENCE (FOCS), Institute of Electrical and Electronics Engineers (IEEE) , 2022, p. 507-518Conference paper (Refereed)
    Abstract [en]

    We study the complexity of determining the edge connectivity of a simple graph with cut queries. We show that (i) there is a bounded-error randomized algorithm that computes edge connectivity with O(n) cut queries, and (ii) there is a bounded-error quantum algorithm that computes edge connectivity with (O) over tilde(root n) cut queries. To prove these results we introduce a new technique, called star contraction, to randomly contract edges of a graph while preserving non-trivial minimum cuts. In star contraction vertices randomly contract an edge incident on a small set of randomly chosen "center" vertices. In contrast to the related 2-out contraction technique of Ghaffari, Nowicki, and Thorup [SODA'20], star contraction only contracts vertex-disjoint star subgraphs, which allows it to be efficiently implemented via cut queries. The O(n) bound from item (i) was not known even for the simpler problem of connectivity, and it improves the O(n log(3) n) upper bound by Rubinstein, Schramm, and Weinberg [ITCS'18]. The bound is tight under the reasonable conjecture that the randomized communication complexity of connectivity is Omega(n log n), an open question since the seminal work of Babai, Frankl, and Simon [FOCS'86]. The bound also excludes using edge connectivity on simple graphs to prove a superlinear randomized query lower bound for minimizing a symmetric submodular function. The quantum algorithm from item (ii) gives a nearlyquadratic separation with the randomized complexity, and addresses an open question of Lee, Santha, and Zhang [SODA'21]. The algorithm can alternatively be viewed as computing the edge connectivity of a simple graph with (O) over tilde(root n) matrix-vector multiplication queries to its adjacency matrix. Finally, we demonstrate the use of star contraction outside of the cut query setting by designing a one-pass semi-streaming algorithm for computing edge connectivity in the complete vertex arrival setting. This contrasts with the edge arrival setting where two passes are required.

  • 23.
    Aronsson, Sanna
    et al.
    FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Artman, Henrik
    FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Brynielsson, Joel
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Lindquist, Sinna
    FOI Swedish Defence Research Agency, Stockholm, Swedena.
    Ramberg, Robert
    Stockholm University, Stockholm, Sweden.
    Design of simulator training: a comparative study of Swedish dynamic decision-making training facilities2021In: Cognition, Technology and Work, ISSN 1435-5558, Vol. 23, no 1, p. 117-130Article in journal (Refereed)
    Abstract [en]

    Simulator training is becoming increasingly important for training of time-critical and dynamic situations. Hence, how simulator training in such domains is planned, carried out and followed up becomes important. Based on a model prescribing such crucial aspects, ten decision-making training simulator facilities have been analyzed from an activity theoretical perspective. The analysis reveals several conflicts that exist between the training that is carried out and the defined training objectives. Although limitations in technology and organization are often alleviated by proficient instructors, it is concluded that there is a need for a structured approach to the design of training to be able to define the competencies and skills that ought to be trained along with relevant measurable training goals. Further, there is a need for a pedagogical model that takes the specifics of simulator training into account. Such a pedagogical model is needed to be able to evaluate the training, and would make it possible to share experiences and make comparisons between facilities in a structured manner.

  • 24.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Banzai, K.
    Department of Computer Science, The University of Tokyo, Tokyo, Japan.
    Gros, Q.
    Polytech Nantes, University of Nantes, Nantes, France.
    Rousset, G.
    Polytech Nantes, University of Nantes, Nantes, France.
    Ma, L.
    Faculty of Information Science and Electrical Engineering, Kyushu University, Fukuoka, Japan.
    Kitamura, T.
    Institute of Information Technology Research, National Institute of Advanced Industrial Science and Technology, Osaka, Japan.
    Hagiya, M.
    Department of Computer Science, The University of Tokyo, Tokyo, Japan.
    Tanabe, Y.
    Department of Library, Archival, and Information Studies, Tsurumi University, Yokohama, Japan.
    Yamamoto, Mitsuharu
    Department of Mathematics and Informatics, Chiba University, Chiba, Japan.
    Model-based testing of Apache ZooKeeper: Fundamental API usage and watchers2019In: Software Testing Verification and Reliability, ISSN 1099-1689, article id e1720Article in journal (Refereed)
    Abstract [en]

    In this paper, we extend work on model‐based testing for Apache ZooKeeper, to handle watchers (triggers) and improve scalability. In a distributed asynchronous shared storage like ZooKeeper, watchers deliver notifications on state changes. They are difficult to test because watcher notifications involve an initial action that sets the watcher, followed by another action that changes the previously seen state.

    We show how to generate test cases for concurrent client sessions executing against ZooKeeper with the tool Modbat. The tests are verified against an oracle that takes into account all possible timings of network communication. The oracle has to verify that there exists a chain of events that triggers both the initial callback and the subsequent watcher notification. We show in detail how the oracle computes whether watch triggers are correct and how the model was adapted and improved to handle these features. Together with a new search improvement that increases both speed and accuracy, we are able to verify large test setups and confirm several defects with our model.

  • 25.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Benali, Adam
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Ramler, Rudolf
    Software Competence Ctr Hagenberg, Hagenberg, Austria..
    Test Benchmarks: Which One Now and in Future?2021In: 2021 IEEE 21ST INTERNATIONAL CONFERENCE ON SOFTWARE QUALITY, RELIABILITY AND SECURITY (QRS 2021), Institute of Electrical and Electronics Engineers (IEEE) , 2021, p. 328-336Conference paper (Refereed)
    Abstract [en]

    To evaluate software testing and program analysis tools, the research community relies on collections of sample programs (benchmarks) containing realistic code examples with defects. We investigated 23 benchmark projects for test generation in common programming languages and looked at how they can be categorized according to attributes such as programming language, number of programs and defects, license, and size. From our studies, it is evident that the development and especially maintenance of benchmarks are a big challenge. Out of the 23 benchmark projects we investigated, only four are still active as of today, and only nine have been updated after their initial release. With the underlying programming languages and platforms constantly evolving (often without full backward compatibility), this creates a challenge when comparing new tools to older ones. To exacerbate the situation, many benchmarks do not fully track the provenance and license of the code they include. Sustainable benchmark collections share these key factors: Open hosting of complete (actual) data allowing community involvement, systematic maintenance of license and authorship data, and a unified machine-readable format for such data.

  • 26.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Csaba Ölveczky, PeterUniversity of Oslo, Norway.
    Welcome from the Chairs2022Conference proceedings (editor) (Other academic)
  • 27.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Olveczky, Peter Csaba
    Univ Oslo, Oslo, Norway..
    Formal Techniques for Safety-Critical Systems (FTSCS 2018) Preface2021In: Science of Computer Programming, ISSN 0167-6423, E-ISSN 1872-7964, Vol. 208, article id 102658Article in journal (Other academic)
  • 28.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Pande, Monali
    KTH.
    Tang, Qiyi
    Imperial Coll London, London, England..
    Visual Analytics for Concurrent Java Executions2019In: Proceedings - 2019 34th IEEE/ACM International Conference on Automated Software Engineering, ASE 2019, Association for Computing Machinery (ACM), 2019, p. 1102-1105, article id 8952488Conference paper (Refereed)
    Abstract [en]

    Analyzing executions of concurrent software is very difficult Even if a trace is available, such traces are very hard to read and interpret. A textual trace contains a lot of data, most of which is not relevant to the issue at hand. Past visualization attempts either do not show concurrent behavior, or result in a view that is overwhelming for the user. We provide a visual analytics tool, VA4JVM, for error traces produced by either the Java Virtual Machine, or by Java Pathfinder. Its key features are a layout that spatially associates events with threads, a zoom function, and the ability to filter event data in various ways. We show in examples how filtering and zooming in can highlight a problem without having to read lengthy textual data.

  • 29.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Parízek, Pavel
    Charles University, Prague, Czech Republic.
    Qu, Daohan
    Nanjing University, Nanjing, China.
    Galgali, Varadraj
    Belgaum, India.
    Yi, Pu Luke
    Stanford University, Stanford, USA.
    JPF: From 2003 to 20232024In: Tools and Algorithms for the Construction and Analysis of Systems - 30th International Conference, TACAS 2024, Held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2024, Proceedings, Springer Science and Business Media Deutschland GmbH , 2024, Vol. 14571, p. 3-22Conference paper (Refereed)
    Abstract [en]

    We give an account of JPF’s current architecture as it has evolved over the last 20 years. Key changes include a modular, extensible design, and Java 11 support. Java 11 brought with it fundamental changes in the language and its runtime, in particular, a new modular library system, different compilation of string expressions to bootstrap methods, and changes in many internal interfaces that allow access to the loaded code and the virtual machine state. These changes required numerous adaptations in JPF to ensure a successful compilation and correct behavior under Java 11.

  • 30.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Rousset, Guillaume
    Model-based Testing of the Java network API2017In: Electronic Proceedings in Theoretical Computer Science, E-ISSN 2075-2180, no 245, p. 46-51Article in journal (Refereed)
    Abstract [en]

    Testing networked systems is challenging. The client or server side cannot be tested by itself. We present a solution using tool "Modbat" that generates test cases for Java's network library java.nio, where we test both blocking and non-blocking network functions. Our test model can dynamically simulate actions in multiple worker and client threads, thanks to a carefully orchestrated design that covers non-determinism while ensuring progress.

  • 31.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Visser, W.
    Java Pathfinder at SV-COMP 2019 (Competition Contribution)2019In: 25th International Conference on Tools and Algorithms for the Construction and Analysis of Systems conference series, TACAS 2019 held as part of the 22nd European Joint Conferences on Theory and Practice of Software, ETAPS 2019, Springer, 2019, Vol. 11429, p. 224-228Conference paper (Refereed)
    Abstract [en]

    This paper gives a brief overview of Java Pathfinder, or jpf-core. We describe the architecture of JPF, its strengths, and how it was set up for SV-COMP 2019.

  • 32.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Ölveczky, P.C.
    Formal Techniques for Safety-Critical Systems (FTSCS 2015)2018In: Science of Computer Programming, ISSN 0167-6423, E-ISSN 1872-7964, Vol. 154, p. 1-2Article in journal (Refereed)
  • 33.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Ölveczky, P.C.
    Formal Techniques for Safety-Critical Systems (FTSCS 2016)2019In: Science of Computer Programming, ISSN 0167-6423, E-ISSN 1872-7964, Vol. 175, p. 35-36Article in journal (Refereed)
  • 34.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Ölveczky, Peter Csaba
    University of Oslo Oslo, Norway.
    Preface2019In: Communications in Computer and Information Science, Springer Nature , 2019, Vol. 1008 CCISChapter in book (Other academic)
  • 35.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Ölveczky, Peter Csaba
    University of Oslo, Norway.
    Preface2023In: Proceedings 44th International Conference on Application and Theory of Petri Nets and Concurrency, PETRI NETS 2023, Association for Computing Machinery (ACM) , 2023Conference paper (Other academic)
  • 36.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Ölveczky, Peter Csaba
    University of Oslo, Norway.
    Welcome from the Chairs2023In: Proceedings of the 9th ACM SIGPLAN International Workshop on Formal Techniques for Safety-Critical Systems - FTSCS 2023, Co-located: SPLASH 2023, Association for Computing Machinery (ACM) , 2023Conference paper (Other academic)
  • 37.
    Ashraf, Adnan
    et al.
    Abo Akad Univ, Fac Sci & Engn, Turku, Finland..
    Majd, Amin
    Abo Akad Univ, Fac Sci & Engn, Turku, Finland..
    Troubitsyna, Elena
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Online Path Generation and Navigation for Swarms of UAVs2020In: Scientific Programming, ISSN 1058-9244, E-ISSN 1875-919X, Vol. 2020, article id 8530763Article in journal (Refereed)
    Abstract [en]

    With the growing popularity of unmanned aerial vehicles (UAVs) for consumer applications, the number of accidents involving UAVs is also increasing rapidly. Therefore, motion safety of UAVs has become a prime concern for UAV operators. For a swarm of UAVs, a safe operation cannot be guaranteed without preventing the UAVs from colliding with one another and with static and dynamically appearing, moving obstacles in the flying zone. In this paper, we present an online, collision-free path generation and navigation system for swarms of UAVs. The proposed system uses geographical locations of the UAVs and of the successfully detected, static, and moving obstacles to predict and avoid the following: (1) UAV-to-UAV collisions, (2) UAV-to-static-obstacle collisions, and (3) UAV-to-moving-obstacle collisions. Our collision prediction approach leverages efficient runtime monitoring and complex event processing (CEP) to make timely predictions. A distinctive feature of the proposed system is its ability to foresee potential collisions and proactively find best ways to avoid predicted collisions in order to ensure safety of the entire swarm. We also present a simulation-based implementation of the proposed system along with an experimental evaluation involving a series of experiments and compare our results with the results of four existing approaches. The results show that the proposed system successfully predicts and avoids all three kinds of collisions in an online manner. Moreover, it generates safe and efficient UAV routes, efficiently scales to large-sized problem instances, and is suitable for cluttered flying zones and for scenarios involving high risks of UAV collisions.

  • 38.
    Asif, Rizwan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Löffel, Hendrik Jan
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Assavasangthong, Vorapol
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Martinelli, Giulio
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Gajland, Phillip
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Rodríguez Gálvez, Borja
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Aerial path planning for multi-vehicles2019In: Proceedings - IEEE 2nd International Conference on Artificial Intelligence and Knowledge Engineering, AIKE 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, p. 267-272, article id 8791733Conference paper (Refereed)
    Abstract [en]

    Unmanned Aerial Vehicles (UAV) are a potential solution to fast and cost efficient package delivery services. There are two types of UAVs, namely fixed wing (UAV-FW) and rotor wing (UAV-RW), which have their own advantages and drawbacks. In this paper we aim at providing different solutions to a collaborating multi-agent scenario combining both UAVs types. We show the problem can be reduced to the facility location problem (FLP) and propose two local search algorithms to solve it: Tabu search and simulated annealing.

  • 39.
    Aslay, Cigdem
    et al.
    Aarhus Univ, Aarhus, Denmark..
    Ciaperoni, Martino
    Aalto Univ, Espoo, Finland..
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Mathioudakis, Michael
    Univ Helsinki, Helsinki, Finland..
    Workload-aware Materialization for Efficient Variable Elimination on Bayesian Networks2021In: 2021 IEEE 37TH INTERNATIONAL CONFERENCE ON DATA ENGINEERING (ICDE 2021), Institute of Electrical and Electronics Engineers (IEEE) , 2021, p. 1152-1163Conference paper (Refereed)
    Abstract [en]

    Bayesian networks are general, well-studied probabilistic models that capture dependencies among a set of variables. Variable Elimination is a fundamental algorithm for probabilistic inference over Bayesian networks. In this paper, we propose a novel materialization method, which can lead to significant efficiency gains when processing inference queries using the Variable Elimination algorithm. In particular, we address the problem of choosing a set of intermediate results to precompute and materialize, so as to maximize the expected efficiency gain over a given query workload. For the problem we consider, we provide an optimal polynomial-time algorithm and discuss alternative methods. We validate our technique using real-world Bayesian networks. Our experimental results confirm that a modest amount of materialization can lead to significant improvements in the running time of queries, with an average gain of 70%, and reaching up to a gain of 99%, for a uniform workload of queries. Moreover, in comparison with existing junction tree methods that also rely on materialization, our approach achieves competitive efficiency during inference using significantly lighter materialization.

  • 40. Assent, I.
    et al.
    Domeniconi, C.
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Hüllermeier, E.
    Introduction to the special issue of the ECML PKDD 2020 journal track2020In: Machine Learning, ISSN 0885-6125, E-ISSN 1573-0565, Vol. 109, no 9-10, p. 1697-1698Article in journal (Refereed)
  • 41.
    Assent, Ira
    et al.
    Aarhus Univ, Aarhus, Denmark..
    Domeniconi, Carlotta
    George Mason Univ, Fairfax, VA 22030 USA..
    Gionis, Aristides
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Huellermeier, Eyke
    Paderborn Univ, Paderborn, Germany..
    Introduction to the special issue of the ECML PKDD 2020 journal track2020In: Data mining and knowledge discovery, ISSN 1384-5810, E-ISSN 1573-756X, Vol. 34, no 5, p. 1235-1236Article in journal (Other academic)
  • 42.
    Atzori, Marco
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Köpp, Wiebke
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Chien, Wei Der
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Massaro, Daniele
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Mallor, Fermin
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Peplinski, Adam
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Rezaei, Mohammadtaghi
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for High Performance Computing, PDC.
    Jansson, Niclas
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Markidis, Stefano
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Laure, E.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Weinkauf, Tino
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    In situ visualization of large-scale turbulence simulations in Nek5000 with ParaView Catalyst2022In: Journal of Supercomputing, ISSN 0920-8542, E-ISSN 1573-0484, Vol. 78, no 3, p. 3605-3620Article in journal (Refereed)
    Abstract [en]

    In situ visualization on high-performance computing systems allows us to analyze simulation results that would otherwise be impossible, given the size of the simulation data sets and offline post-processing execution time. We develop an in situ adaptor for Paraview Catalyst and Nek5000, a massively parallel Fortran and C code for computational fluid dynamics. We perform a strong scalability test up to 2048 cores on KTH’s Beskow Cray XC40 supercomputer and assess in situ visualization’s impact on the Nek5000 performance. In our study case, a high-fidelity simulation of turbulent flow, we observe that in situ operations significantly limit the strong scalability of the code, reducing the relative parallel efficiency to only ≈ 21 % on 2048 cores (the relative efficiency of Nek5000 without in situ operations is ≈ 99 %). Through profiling with Arm MAP, we identified a bottleneck in the image composition step (that uses the Radix-kr algorithm) where a majority of the time is spent on MPI communication. We also identified an imbalance of in situ processing time between rank 0 and all other ranks. In our case, better scaling and load-balancing in the parallel image composition would considerably improve the performance of Nek5000 with in situ capabilities. In general, the result of this study highlights the technical challenges posed by the integration of high-performance simulation codes and data-analysis libraries and their practical use in complex cases, even when efficient algorithms already exist for a certain application scenario.

  • 43.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Bhangale, Amey
    Univ Calif Riverside, Riverside, CA 92521 USA.;Weizmann Inst Sci, Rehovot, Israel..
    Potukuchi, Aditya
    Rutgers State Univ, Piscataway, NJ USA..
    Improved Inapproximability of Rainbow Coloring2020In: Proceedings of the 2020 ACM-SIAM Symposium on Discrete Algorithms, SODA 2020, Society for Industrial & Applied Mathematics (SIAM) , 2020, p. 1479-1495Conference paper (Refereed)
    Abstract [en]

    A rainbow q-coloring of a k-uniform hypergraph is a q-coloring of the vertex set such that every hyperedge contains all q colors. We prove that given a rainbow (k - 2left perpendicular root kright perpendicular)-colorable k-uniform hypergraph, it is NP-hard to find a normal 2-coloring. Previously, this was only known for rainbow left perpendiculark/2right perpendicular-colorable hypergraphs (Guruswami and Lee, SODA 2015). We also study a generalization which we call rainbow (q; p)-coloring, defined as a coloring using q colors such that every hyperedge contains at least p colors. We prove that given a rainbow (k - left perpendicular root kcright perpendicular; k - left perpendicular3 root kcright perpendicular)-colorable k uniform hypergraph, it is NP-hard to find a normal c-coloring for any c = o(k). The proof of our second result relies on two combinatorial theorems. One of the theorems was proved by Sarkaria (J. Comb. Theory, Ser. B 1990) using topological methods and the other theorem we prove using a generalized BorsukUlam theorem.

  • 44.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Brown-Cohen, Jonah
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Håstad, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Optimal inapproximability with universal factor graphs2021In: Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms, Association for Computing Machinery , 2021, p. 434-453Conference paper (Refereed)
    Abstract [en]

    The factor graph of an instance of a constraint satisfaction problem (CSP) is the bipartite graph indicating which variables appear in each constraint. An instance of the CSP is given by the factor graph together with a list of which predicate is applied for each constraint. We establish that many Max-CSPs remain as hard to approximate as in the general case even when the factor graph is fixed (depending only on the size of the instance) and known in advance. Examples of results obtained for this restricted setting are: 1. Optimal inapproximability for Max-3-Lin and Max-3-Sat (Håstad, J. ACM 2001). 2. Approximation resistance for predicates supporting pairwise independent subgroups (Chan, J. ACM 2016). 3. Hardness of the “(2 + ε)-Sat” problem and other Promise CSPs (Austrin et al., SIAM J. Comput. 2017). The main technical tool used to establish these results is a new way of folding the long code which we call “functional folding”.

  • 45.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Chung, Hao
    Carnegie Mellon Univ, Pittsburgh, PA USA..
    Chung, Kai-Min
    Acad Sinica, Taipei, Taiwan..
    Fu, Shiuan
    Acad Sinica, Taipei, Taiwan..
    Lin, Yao-Ting
    Acad Sinica, Taipei, Taiwan..
    Mahmoody, Mohammad
    Univ Virginia, Charlottesville, VA USA..
    On the Impossibility of Key Agreements from Quantum Random Oracles2022In: Advances In Cryptology - CRYPTO 2022, PT II / [ed] Dodis, Y Shrimpton, T, Springer Nature , 2022, Vol. 13508, p. 165-194Conference paper (Refereed)
    Abstract [en]

    We study the following question, first publicly posed by Hosoyamada and Yamakawa in 2018. Can parties A, B with quantum computing power and classical communication rely only on a random oracle (that can be queried in quantum superposition) to agree on a key that is private from eavesdroppers? We make the first progress on the question above and prove the following. - When only one of the parties A is classical and the other party B is quantum powered, as long as they ask a total of d oracle queries and agree on a key with probability 1, then there is always a way to break the key agreement by asking O(d(2)) number of classical oracle queries. - When both parties can make quantum queries to the random oracle, we introduce a natural conjecture, which if true would imply attacks with poly(d) classical queries to the random oracle. Our conjecture, roughly speaking, states that the multiplication of any two degree-d real-valued polynomials over the Boolean hypercube of influence at most delta = 1/poly (d) is nonzero. We then prove our conjecture for exponentially small influences, which leads to an (unconditional) classical 2(O(md))-query attack on any such key agreement protocol, where m is the oracle's output length. - Since our attacks are classical, we then ask whether it is always possible to find classical attacks on key agreements with imperfect completeness in the quantum random oracle model. We prove a barrier for this approach, by showing that if the folklore "Simulation Conjecture" (first formally stated by Aaronson and Ambainis in 2009) about the possibility of simulating efficient-query quantum algorithms using efficient-query classical algorithms is false, then there is in fact such a secure key agreement in the quantum random oracle model that cannot be broken classically.

  • 46.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Kaski, P.
    Kubjas, K.
    Tensor network complexity of multilinear maps2019In: Leibniz International Proceedings in Informatics, LIPIcs, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2019Conference paper (Refereed)
    Abstract [en]

    We study tensor networks as a model of arithmetic computation for evaluating multilinear maps. These capture any algorithm based on low border rank tensor decompositions, such as O(nω+ϵ) time matrix multiplication, and in addition many other algorithms such as O(nlog n) time discrete Fourier transform and O∗(2n) time for computing the permanent of a matrix. However tensor networks sometimes yield faster algorithms than those that follow from low-rank decompositions. For instance the fastest known O(n(ω+ϵ)t) time algorithms for counting 3t-cliques can be implemented with tensor networks, even though the underlying tensor has border rank n3t for all t ≥ 2. For counting homomorphisms of a general pattern graph P into a host graph on n vertices we obtain an upper bound of O(n(ω+ϵ) bw(P)/2) where bw(P) is the branchwidth of P. This essentially matches the bound for counting cliques, and yields small improvements over previous algorithms for many choices of P. While powerful, the model still has limitations, and we are able to show a number of unconditional lower bounds for various multilinear maps, including: (a) an Ω(nbw(P)) time lower bound for counting homomorphisms from P to an n-vertex graph, matching the upper bound if ω = 2. In particular for P a v-clique this yields an Ω(nd2v/3e) time lower bound for counting v-cliques, and for P a k-uniform v-hyperclique we obtain an Ω(nv) time lower bound for k ≥ 3, ruling out tensor networks as an approach to obtaining non-trivial algorithms for hyperclique counting and the Max-3-CSP problem. (b) an Ω(20.918n) time lower bound for the permanent of an n × n matrix.

  • 47.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Kaski, Petteri
    Koivisto, Mikko
    Nederlof, Jesper
    Sharper Upper Bounds for Unbalanced Uniquely Decodable Code Pairs2018In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 64, no 2, p. 1368-1373Article in journal (Refereed)
    Abstract [en]

    Two sets of 0-1 vectors of fixed length form a uniquely decodeable code pair if their Cartesian product is of the same size as their sumset, where the addition is pointwise over integers. For the size of the sumset of such a pair, van Tilborg has given an upper bound in the general case. Urbanke and Li, and later Ordentlich and Shayevitz, have given better bounds in the unbalanced case, that is, when either of the two sets is sufficiently large. Improvements to the latter bounds are presented.

  • 48.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Kaski, Petteri
    Department of Computer Science, Aalto University, Finland.
    Kubjas, Kaie
    Department of Mathematics and Systems Analysis, Aalto University, Finland.
    Tensor network complexity of multilinear maps2022In: Theory of Computing, E-ISSN 1557-2862, Vol. 18, article id 16Article in journal (Refereed)
    Abstract [en]

    We study tensor networks as a model of arithmetic computation for evaluating multilinear maps. hese capture any algorithm based on low-rank tensor decompositions, such as O(nω+ϵ) time matrix multiplication, and in addition many other algorithms such as O(nlogn) time discrete Fourier transform and O∗(2n) time for computing the permanent of a matrix. However, tensor networks sometimes yield faster algorithms than those that follow from low-rank decompositions. For instance the fastest known O(n(ω+ϵ)t) time algorithms for counting 3t-cliques can be implemented with tensor networks, even though the underlying tensor has rank n3t for all t≥2. For counting homomorphisms of a general pattern graph P into a host graph on n vertices we obtain an upper bound of O(n(ω+ϵ)bw(P)/2) where bw(P) is the branchwidth of P. This essentially matches the bound for counting cliques, and yields small improvements over previous algorithms for many choices of P. While powerful, the model still has limitations, and we are able to show a number of unconditional lower bounds for various multilinear maps, including the following. [(a)] An Ω(nbw(P)) time lower bound for counting homomorphisms from P to an n-vertex graph, matching the upper bound if ω=2. In particular for P a v-clique this yields an Ω(n⌈2v/3⌉) time lower bound for counting v-cliques, and for P a k-uniform v-hyperclique we obtain an Ω(nv) time lower bound for k ≥ 3, ruling out tensor networks as an approach to obtaining non-trivial algorithms for hyperclique counting and the Max-3-CSP problem. [(b)] An Ω(20.918n) time lower bound for the determinant and the permanent of an n×n matrix.

  • 49.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Risse, Kilian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Perfect Matching in Random Graphs is as Hard as Tseitin2022In: Proceedings of the 2022 Annual ACM-SIAM Symposium on Discrete Algorithms (SODA), Association for Computing Machinery (ACM), 2022, p. 979-1012Conference paper (Refereed)
    Abstract [en]

    We study the complexity of proving that a sparse random regular graph on an odd number of vertices does not have a perfect matching, and related problems involving each vertex being matched some pre-specified number of times. We show that this requires proofs of degree (n= log n) in the Polynomial Calculus (over fields of characteristic 6= 2) and Sum-of-Squares proof systems, and exponential size in the bounded-depth Frege proof system. This resolves a question by Razborov asking whether the Lovasz-Schrijver proof system requires nrounds to refute these formulas for some > 0. The results are obtained by a worst-case to averagecase reduction of these formulas relying on a topological embedding theorem which may be of independent interest.

  • 50.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Risse, Kilian
    EPFL, Lausanne, Switzerland.
    Sum-Of-Squares Lower Bounds for the Minimum Circuit Size Problem2023In: 38th Computational Complexity Conference, CCC 2023, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2023, Vol. 264, article id 31Conference paper (Refereed)
    Abstract [en]

    We prove lower bounds for the Minimum Circuit Size Problem (MCSP) in the Sum-of-Squares (SoS) proof system. Our main result is that for every Boolean function f : (0, 1)n → (0, 1), SoS requires degree Ω(s1−ϵ) to prove that f does not have circuits of size s (for any s > poly(n)). As a corollary we obtain that there are no low degree SoS proofs of the statement NP ⊈ P/poly. We also show that for any 0 < α < 1 there are Boolean functions with circuit complexity larger than 2nα but SoS requires size 22Ω(nα) to prove this. In addition we prove analogous results on the minimum monotone circuit size for monotone Boolean slice functions. Our approach is quite general. Namely, we show that if a proof system Q has strong enough constraint satisfaction problem lower bounds that only depend on good expansion of the constraint-variable incidence graph and, furthermore, Q is expressive enough that variables can be substituted by local Boolean functions, then the MCSP problem is hard for Q.

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