Optimization Group

Prof. Dr. Stefan Ruzika

Address

Paul-Ehrlich-Straße
Building: 14
Room: 457
67663 Kaiserslautern

P.O. Box: 3049
67653 Kaiserslautern

Contact

Tel.: +49 631 205 4423

Fax: +49 631 205 4737

E-Mail: stefan.ruzika@math.rptu.de

I am the director of the Competence Center for Mathematical Modeling in STEM Projects in Schools (KOMMS). Click here to visit the KOMMS website.

I am also spokesperson of the Research Training Group Mathematics of Interdisciplinary Multiobjective Optimization (MIMO), which is funded by the German Research Foundation and will start its research work in October 2024. Information on the new Research Training Group can be found here.

Lectures and seminars

During the winter semester 2024/25 the following lectures and seminars will be offered by me:

I also supervise Bachelor's and Master's theses. If you are interested in this, please contact me by e-mail.

Research Interests

  • Multi-criteria Optimization
  • Integer and Combinatorial Optimization
  • Mathematical Modelling
  • Network Optimization Problems
  • Approximation Algorithms

Research projects

Ageing Smart

Decision Support for the generation baby-boomer

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AMPaPro

Approximation of Multi-Parametric Programming Problems

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RTG 2982: MIMO

Mathematics of Interdisciplinary Multiobjective Optimization

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MAL-i

Mathematical Adaptive Learningsystems Enhanced by Eye-Tracking

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SchuMaMoMINT

School Development for Mathematical Modeling in STEM Subjects

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WebStuPlan

Instrument for the presentation of study progression and student counseling

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Executive functions (selection)

Curriculum Vitae

  • since 2017: Full Professor in the Department of Mathematics at the Rhineland-Palatinate Technical University Kaiserslautern-Landau (RPTU), previously: TU Kaiserslautern

  • 2012-2017: Full Professor of Mathematics, University of Koblenz-Landau

  • 2009-2010: Substitute Professor at the Chair of Optimization, University of Wuppertal, Germany

  • 2008-2012: Junior Professor for Mathematical Optimization and Applications, TU Kaiserslautern

  • 2007: Dr.rer.nat. (PhD-equivalent), TU Kaiserslautern
    Thesis: On Multiple Objective Combinatorial Optimization

  • 2003-2007: Research Assistant, TU Kaiserslautern

  • 2003: Diploma in Mathematics, TU Kaiserslautern

  • 2002: Master of Science, Clemson University, South Carolina, USA

  • 2001-2002: Studies of Mathematics, Clemson University, South Carolina, USA

  • 1998-2003: Studies of Mathematics and Computer Science, TU Kaiserslautern

Publications

  • On the hardness of covering-interdiction problems
    N. Fröhlich, S. Ruzika,
    Theoretical Computer Science 871, pp. 1-15 (2021)

  • A Reduced-Complexity Projection Algorithm for ADMM-based LP Decoding
    F. Gensheimer, T. Dietz, K. Kraft, S. Ruzika, N. Wehn,
    IEEE Transactions on Information Theory (2020)

  • The binary knapsack problem with qualitative levels
    L. E. Schäfer, T. Dietz, M. Barbati, J. Figueira, S. Greco, S. Ruzika,
    European Journal of Operational Research (2020)

  • An approximation algorithm for a general class of parametric optimization problems
    C. Bazgan, A. Herzel, S. Ruzika, C. Thielen, D. Vanderpooten,
    Journal of Combinatorial Optimization, pp. 1-31 (2020)

  • One-exact approximate Pareto sets
    A. Herzel, C. Bazgan, S. Ruzika, C. Thielen, D. Vanderpooten,
    Journal of Global Optimization, pp. 1-29 (2020)

  • On the rectangular knapsack problem: approximation of a specific quadratic knapsack problem
    B. Schulze, M. Stiglmayr, L. Paquete, C. M. Fonseca, D. Willems, S. Ruzika,
    Mathematical Methods of Operations Research, pp. 1-26 (2020)

  • An inner approximation method to compute the weight set decomposition of a triobjective mixed-integer problem
    P. Halffmann, T. Dietz, A. Przybylski, S. Ruzika,
    Journal of Global Optimization (2020)

  • Sparsifying parity-check matrices
    L. Russo, T. Dietz, J. Figueira, A. P. Francisco, S. Ruzika,
    Applied Soft Computing 96, pp. 106601 (2020)

  • Maximising the clustering coefficient of networks and the effects on habitat network robustness
    H. Heer, L. Streib, R. B. Schäfer, S. Ruzika,
    Plos one 15, pp. e0240940 (2020)

  • Shortest paths with ordinal weights
    L. E. Schäfer, T. Dietz, N. Fröhlich, S. Ruzika, J. R. Figueira,
    European Journal of Operational Research 280, pp. 1160-1170 (2020)

  • On the p-hub interdiction problem
    T. Ullmert, S. Ruzika, A. Schöbel,
    Computers & Operations Research 124, pp. 105056 (2020)

  • How does habitat connectivity influence the colonization success of a hemimetabolous aquatic insect? - A modeling approach
    L. Streib, M. Kattwinkel, H. Heer, S. Ruzika, R. B. Schäfer,
    Ecological Modelling 416, pp. 108909 (2020)

  • Introducing multiobjective complex systems
    T. Dietz, K. Klamroth, K. Kraus, S. Ruzika, L. E. Schäfer, B. Schulze, M. Stiglmayr, M. M. Wiecek,
    European Journal of Operational Research 280, pp. 581-596 (2020)

  • Unified Education: Medienbildung entlang der Lehrerbildungskette-Maßnahmen im Rahmen der Qualitätsoffensive Lehrerbildung der TU Kaiserslautern
    M. Bracke, C. Gomez-Tutor, J. Kuhn, S. Ruzika,
    Mitteilungen der Gesellschaft für Didaktik der Mathematik 45, pp. 33-38 (2019)

  • Optimisation Model of Dispersal Simulations on a Dendritic Habitat Network
    H. Heer, L. Streib, M. Kattwinkel, R. B. Schäfer, S. Ruzika,
    Scientific Reports 9, pp. 1-11 (2019)

  • Approximation Schemes For the Parametric Knapsack Problem
    A. Giudici, P. Halffmann, S. Ruzika, C. Thielen,
    Information Processing Letters 120, pp. 11-15 (2017)

  • A General Approximation Method for Bicriteria Minimization Problems
    P. Halffmann, S. Ruzika, C. Thielen, D. Willems,
    Theoretical Computer Science 695, pp. 1-15 (2017)

  • Multiobjective optimization for interwoven systems
    K. Klamroth, S. Mostaghim, B. Naujoks, S. Poles, R. Purshouse, G. Rudolph, S. Ruzika, S. Sayin, M. M. Wiecek, X. Yao,
    Journal of Multi-Criteria Decision Analysis 24, pp. 71-81 (2017)

  • A coverage-based Box-Algorithm to compute a representation for optimization problems with three objective functions
    T. Kuhn, S. Ruzika,
    Journal of Global Optimization 67, pp. 581-600 (2017)

  • Shortest Paths with Shortest Detours
    C. Torchiani, J. Ohst, D. Willems, S. Ruzika,
    Journal of Optimization Theory and Applications 174, pp. 858-874 (2017)

  • Easy to say they are Hard, but Hard to see they are Easy - Towards a Categorization of Tractable Multiobjective Combinatorial Optimization Problems
    J. Figueira, C. M. Fonseca, P. Halffmann, K. Klamroth, L. Paquete, S. Ruzika, B. Schulze, M. Stiglmayr, D. Willems,
    Journal of Multi-Criteria Decision Analysis 24, pp. 82-98 (2017)

  • A hybrid and multiscale approach to model and simulate mobility in the context of public events
    D. H. Biedermann, C. Torchiani, P. M. Kielar, D. Willems, O. Handel, S. Ruzika, A. Borrmann,
    Transportation Research Procedia 19, pp. 350-363 (2016)

  • Evacuation modeling: a case study on linear and nonlinear network flow models
    S. Göttlich, S. Kühn, J. Ohst, S. Ruzika,
    EURO journal on computational optimization 4, pp. 219-239 (2016)

  • Hypervolume subset selection in two dimensions: Formulations and algorithms
    T. Kuhn, C. M. Fonseca, L. Paquete, S. Ruzika, M. M. Duarte, J. Figueira,
    Evolutionary Computation 24, pp. 411-425 (2016)

  • Fahrgastwechselzeiten von Shuttlebussen
    C. Torchiani, M. J. Seitz, D. Willems, S. Ruzika, G. Köster,
    H. TUM-I1517. TU München: Universität Koblenz-Landau 2015 (2015)

  • Comments on: Static and dynamic source locations in undirected networks
    S. Ruzika, C. Torchiani,
    TOP 23, pp. 655-659 (2015)

  • Multiple objective branch and bound for mixed 0-1 linear programming: Corrections and improvements for the biobjective case
    T. Vincent, F. Seipp, S. Ruzika, A. Przybylski, X. Gandibleux,
    Computers & Operations Research 40, pp. 498-509 (2013)

  • Bidirectional coupling of macroscopic and microscopic pedestrian evacuation models
    A. Borrmann, A. Kneidl, G. Köster, S. Ruzika, M. Thiemann,
    Safety science 50, pp. 1695-1703 (2012)

  • Generalized multiple objective bottleneck problems
    J. Gorski, K. Klamroth, S. Ruzika,
    Operations Research Letters 40, pp. 276-281 (2012)

  • Mathematical programming decoding of binary linear codes: Theory and algorithms
    M. Helmling, S. Ruzika, A. Tanatmis,
    IEEE Transactions on Information Theory 58, pp. 4753-4769 (2012)

  • Committee selection under weight constraints
    C. Klamler, U. Pferschy, S. Ruzika,
    Mathematical Social Sciences 64, pp. 48-56 (2012)

  • Min-Max quickest path problems
    S. Ruzika, M. Thiemann,
    Networks 60, pp. 253-258 (2012)

  • Evacuation dynamics influenced by spreading hazardous material
    S. Göttlich, S. Kühn, J. Ohst, S. Ruzika, M. Thiemann,
    Networks & Heterogeneous Media 6, pp. 443-464 (2011)

  • Connectedness of efficient solutions in multiple objective combinatorial optimization
    J. Gorski, K. Klamroth, S. Ruzika,
    Journal of Optimization Theory and Applications 150, pp. 475-497 (2011)

  • Earliest arrival flows on series-parallel graphs
    S. Ruzika, H. Sperber, M. Steiner,
    Networks 57, pp. 169-173 (2011)

  • On k-max-optimization
    J. Gorski, S. Ruzika,
    Operations Research Letters 37, pp. 23-26 (2009)

  • Improved epsilon-constraint method for multiobjective programming
    M. Ehrgott, S. Ruzika,
    Journal of Optimization Theory and Applications 138, pp. 375 (2008)

  • Finding representative systems for discrete bicriterion optimization problems
    H. W. Hamacher, C. Pedersen, S. Ruzika,
    Operations Research Letters 35, pp. 336-344 (2007)

  • Multiple objective minimum cost flow problems: A review
    H. W. Hamacher, C. Pedersen, S. Ruzika,
    European Journal of Operational Research 176, pp. 1404-1422 (2007)

  • An Exact Algorithm for Solving Weight-Constrained Combinatorial Optimization Problems
    S. Ruzika,
    Electronic Notes in Discrete Mathematics, pp. 143-144 (2006)

  • Algorithms for time-dependent bicriteria shortest path problems
    H. W. Hamacher, S. Ruzika, S. A. Tjandra,
    Discrete optimization 3, pp. 238-254 (2006)

  • Approximation methods in multiobjective programming
    S. Ruzika, M. M. Wiecek,
    Journal of optimization theory and applications 126, pp. 473-501 (2005)

  • Detecting local convexity on the Pareto surface
    G. Fadel, Y. Li, S. Konda, M. M. Wiecek, S. Ruzika,
    Journal of Multi-Criteria Decision Analysis 11, pp. 45-54 (2002)

  • J. Andersen, M. Baum, C. Dictus, A. Greubel, L. Knippertz, J. Krüger, I. Neumann, B. Priemer, S. Ruzika, J. Schulz, others
    Critical Thinking--Gelegenheit für MINT-Lernen in der Zukunft?
    Die Zukunft des MINT-Lernens--Band 1: Perspektiven auf (digitalen) MINT-Unterricht und Lehrkräftebildung, Springer Berlin Heidelberg Berlin, Heidelberg, pp. 43-57 (2022)

  • S. Becker, L. Knippertz, J. Kuhn, L. Kuntz, S. Ruzika
    Blickdatenanalyse bei der Interpretation linearer Graphen im mathematischen und physikalischen Kontext
    Die Zukunft des MINT-Lernens--Band 1: Perspektiven auf (digitalen) MINT-Unterricht und Lehrkräftebildung, Springer Berlin Heidelberg Berlin, Heidelberg, pp. 181-192 (2022)

  • K. Kennel, S. Becker, P. Klein, S. Küchemann, J. Kuhn, S. Ruzika
    Blickbewegungen beim grafischen Ableiten--Lassen sich Fehler durch Eye-Tracking-Daten vorhersagen und elaborieren?
    Eye-Tracking in der Mathematik-und Naturwissenschaftsdidaktik: Forschung und Praxis, Springer, pp. 125-143 (2022)

  • S. Küchemann, N. Cullmann, S. Kovac, S. Becker, P. Klein, K. Kennel, S. Ruzika, J. Kuhn
    Blickverhalten beim Lernen und Problemlösen mit Graphen--Ein Literaturüberblick bis 2020
    Eye-Tracking in der Mathematik-und Naturwissenschaftsdidaktik, Springer, pp. 177-192 (2022)

  • L. E. Schäfer, S. Ruzika
    On Variants of the Single-criterion and Multiobjective Near-Shortest Paths Problem
    Multikriterielle Optimierung und Entscheidungsunterstützung, Springer Fachmedien Wiesbaden, pp. 17-30 (2019)

  • K. Küfer, S. Ruzika, P. Halffmann
    Multikriterielle Optimierung und Entscheidungsunterstützung: Tagungsband GOR Entscheidungstheorie und-praxis 2018
    Springer-Verlag (2019)

  • S. Ruzika, V. Klöckner, S. Gecks
    Wie man einen Testsieger kürt
    Digitale Werkzeuge, Simulationen und mathematisches Modellieren, Springer, pp. 229-252 (2018)

  • D. Willems, O. Zehner, S. Ruzika
    On a Technique for Finding Running Tracks of Specific Length in a Road Network
    Operations Research Proceedings 2017, Springer, pp. 333-338 (2018)

  • S. Ruzika, H. Siller, M. Bracke
    Evakuierungsszenarien in Modellierungswochen - ein interessantes und spannendes Thema für den Mathematikunterricht
    Neue Materialien für einen realitätsbezogenen Mathematikunterricht 3, Springer, pp. 181-190 (2017)

  • S. Ruzika, H. Siller, M. Bracke
    Evakuierungsszenarien in Modellierungswochen--ein interessantes und spannendes Thema für den Mathematikunterricht
    Neue Materialien für einen realitätsbezogenen Mathematikunterricht 3, Springer, pp. 181-190 (2017)

  • S. Göttlich, S. Kühn, J. P. Ohst, S. Ruzika
    Influence of Spreading Hazardous Material in Macroscopic Evacuation Dynamics: A Proof of Concept
    Pedestrian and Evacuation Dynamics 2012, Springer, pp. 275-282 (2014)

  • A. Kneidl, M. Thiemann, A. Borrmann, S. Ruzika, H. W. Hamacher, G. Köster, E. Rank
    Bidirectional coupling of macroscopic and microscopic approaches for pedestrian behavior prediction
    Pedestrian and Evacuation Dynamics, Springer, pp. 459-470 (2011)

  • K. Leiner, S. Ruzika
    Quickest cluster flow problems on tree networks
    Network Optimization, Springer, pp. 243-255 (2011)

  • S. Ruzika, M. Thiemann
    Reliable and restricted quickest path problems
    Network Optimization, Springer, pp. 309-314 (2011)

  • H. W. Hamacher, S. Heller, W. Klein, G. Köster, S. Ruzika
    A sandwich approach for evacuation time bounds
    Pedestrian and Evacuation Dynamics, Springer, pp. 503-513 (2011)

  • H. W. Hamacher, K. Leiner, S. Ruzika
    Quickest cluster flow problems
    Pedestrian and Evacuation Dynamics, Springer, pp. 327-336 (2011)

  • H. W. Hamacher, S. Ruzika
    Flach spielen, hoch gewinnen: Fußball und Wissenschaft
    Shaker (2010)

  • S. Ruzika, H. W. Hamacher
    A survey on multiple objective minimum spanning tree problems
    Algorithmics of Large and Complex Networks, Springer, pp. 104-116 (2009)

  • S. Ruzika
    On multiple objective combinatorial optimization
    Verlag Dr. Hut (2007)
  • L. Knippertz, S. Becker, J. Kuhn, S. Ruzika
    Gaze pattern analysis to reveal student difficulties in interpreting kinematic graphs
    Twelfth Congress of the European Society of Research in Mathematics Education (CERME12) (2022)

  • A. Greubel, H. Siller, S. Ruzika, L. Knippertz
    Teaching Mathematical Modeling with Computing Technology: Presentation of a Course based on Evacuations
    Proceedings of the 17th Workshop in Primary and Secondary Computing Education, pp. 1-6 (2022)

  • L. Albert, N. Fröhlich, N. Hausbrand, S. Henninger, T. Maurer, S. Ruzika
    Human-biometeorologisch angepasste Routenführungen durch mathematische Optimierung
    Mobility, Knowledge and Innovation Hubs in Urban and Regional Development. Proceedings of REAL CORP 2022, 27th International Conference on Urban Development, Regional Planning and Information Society, pp. 427-435 (2022)

  • M. Stiewing, T. Weber, K. Mangels, S. Ruzika, N. Fröhlich, N. Hausbrandt
    „Black Box Babyboomer”--Was kommt auf Kommunen zu? Decision Support System mit Hilfe mathematischer Erreichbarkeitsmodellierung medizinischer Versorgungsstandorte
    Mobility, Knowledge and Innovation Hubs in Urban and Regional Development. Proceedings of REAL CORP 2022, 27th International Conference on Urban Development, Regional Planning and Information Society, pp. 131-141 (2022)

  • L. Schneider, R. B. Ferri, S. Ruzika
    How knowledge about ideal-typical modelling processes affects phase transitions in individual modelling routes
    Twelfth Congress of the European Society for Research in Mathematics Education (2022)

  • L. E. Schäfer, T. Dietz, M. V. Natale, S. Ruzika, S. O. Krumke, C. M. Fonseca
    The Bicriterion Maximum Flow Network Interdiction Problem in s-t-Planar Graphs
    Operations Research Proceedings 2019, pp. 133-139 (2020)

  • P. Schiewe, A. Schöbel, S. Ruzika
    Kosten oder Reisezeit? Bikriterielle Optimierung der integrierten Fahr- und Umlaufplanung
    Preprint Heureka'21 (2020)

  • C. Bazgan, A. Herzel, S. Ruzika, C. Thielen, D. Vanderpooten
    An FPTAS for a General Class of Parametric Optimization Problems
    International Computing and Combinatorics Conference, pp. 25-37 (2019)

  • S. Ruzika, L. Schneider
    On the role of multicriteria decision support in mathematical modelling
    Eleventh Congress of the European Society for Research in Mathematics Education 24 (2019)

  • F. Gensheimer, T. Dietz, S. Ruzika, K. Kraft, N. Wehn
    Improved Maximum-Likelihood Decoding Using Sparse Parity-Check Matrices
    2018 25th International Conference on Telecommunications (ICT), pp. 236-240 (2018)

  • F. Gensheimer, T. Dietz, S. Ruzika, K. Kraft, N. Wehn
    A Low-Complexity Projection Algorithm for ADMM-Based LP Decoding
    2018 IEEE 10th International Symposium on Turbo Codes & Iterative Information Processing (ISTC), pp. 1-5 (2018)

  • D. H. Biedermann, C. Torchiani, P. M. Kielar, D. Willems, O. Handel, S. Ruzika, A. Borrmann
    A hybrid and multiscale approach to model and simulate mobility in the context of public events
    Transportation Research Procedia (19), pp. 350-363 (2016)

  • F. Gensheimer, S. Ruzika, S. Scholl, N. Wehn
    ADMM versus simplex algorithm for LP decoding
    9th International Symposium on Turbo Codes and Iterative Information Processing (ISTC), 2016, pp. 211-215 (2016)

  • F. Gensheimer, S. Ruzika, S. Scholl, N. Wehn
    A simplex algorithm for LP decoding hardware
    Personal, Indoor, and Mobile Radio Communication (PIMRC), 2014 IEEE 25th Annual International Symposium on, pp. 790-794 (2014)

  • M. Helmling, E. Rosnes, S. Ruzika, S. Scholl
    Efficient maximum-likelihood decoding of linear block codes on binary memoryless channels
    Information Theory (ISIT), 2014 IEEE International Symposium on, pp. 2589-2593 (2014)

  • S. Scholl, F. Kienle, M. Helmling, S. Ruzika
    Integer programming as a tool for analysis of channel codes
    Systems, Communication and Coding (SCC), Proceedings of 2013 9th International ITG Conference on, pp. 1-6 (2013)

  • M. Helmling, S. Ruzika
    Towards combinatorial LP turbo decoding
    2013 IEEE International Symposium on Information Theory Proceedings (ISIT), pp. 1491-1495 (2013)

  • S. Scholl, F. Kienle, M. Helmling, S. Ruzika
    ML vs. BP decoding of binary and non-binary LDPC codes
    Turbo Codes and Iterative Information Processing (ISTC), 2012 7th International Symposium on, pp. 71-75 (2012)

  • A. Tanatmis, S. Ruzika, F. Kienle
    A Lagrangian relaxation based decoding algorithm for LTE turbo codes
    Turbo Codes and Iterative Information Processing (ISTC), 2010 6th International Symposium on, pp. 369-373 (2010)

  • M. Punekar, F. Kienle, N. Wehn, A. Tanatmis, S. Ruzika, H. W. Hamacher
    Calculating the minimum distance of linear block codes via integer programming
    Turbo Codes and Iterative Information Processing (ISTC), 2010 6th International Symposium on, pp. 329-333 (2010)

  • Y. Ji, F. Seipp, A. Borrmann, S. Ruzika, E. Rank
    Mathematical modeling of earthwork optimization problems
    Proc. of the International Conference on Computing in Civil and Building Engineering (ICCCBE) (2010)

  • A. Tanatmis, S. Ruzika, M. Punekar, F. Kienle
    Numerical comparison of IP formulations as ML decoders
    Communications (ICC), 2010 IEEE International Conference on, pp. 1-5 (2010)

  • C. Klamler, U. Pferschy, S. Ruzika
    Committee selection with a weight constraint based on lexicographic rankings of individuals
    International Conference on Algorithmic DecisionTheory, pp. 50-61 (2009)

  • A. Tanatmis, S. Ruzika, H. W. Hamacher, M. Punekar, F. Kienle, N. Wehn
    Valid inequalities for binary linear codes
    IEEE International Symposium on Information Theory, 2009. ISIT 2009., pp. 2216-2220 (2009)

  • A. Tanatmis, S. Ruzika, H. W. Hamacher, M. Punekar, F. Kienle, N. Wehn
    A separation algorithm for improved LP-decoding of linear block codes
    5th International Symposium on Turbo Codes and Related Topics, 2008, pp. 37-42 (2008)

  • S. Baumgartner, E. O. Gavriliouk, H. W. Hamacher, T. Meyer, S. Ruzika
    Hub location's tool box: Integer programming, heuristics, aggregation, multiobjective optimization
    Extended Abstract, ISOLDE X Meeting, Sevilla, Spain (2005)