Find all the recent news concerning the Decision Support & Operations Research group here!

  • Open PhD position in Operations Research (graph theory / combinatorial optimization / mathematical programming) in our group

    A PhD position is opened at the Department of Informatics at the University of Fribourg (Switzerland) within the Decision Support & Operations Research group. The successful candidate will work on problems related to graph theory, combinatorial optimization and/or mathematical programming. Our research group is, for example, active in structural and algorithmic graph theory, machine and employee scheduling, and vehicle routing. The specific research projects will be defined together with the PhD student based on her/his interests and skills and on the fit within the research scope of the group.

    As a PhD student, the candidate has some teaching responsibilities, both at bachelor and master level. In particular, she/he will be responsible for the exercise sessions of some of our courses (e.g., algorithms, graph theory and integer programming), supervise student projects and help with administrative tasks.

    The PhD position is fully funded. Starting date is September 1, 2020 (with some flexibility). We offer a competitive gross salary starting at 58’000 CHF per year. The PhD student will also get the opportunity to attend international conferences and to travel and learn from leading experts through our wide network of academic and industry collaborations.

    The candidate should have a Master’s degree in Operations Research, Mathematics, Computer Science, Information Systems or related domain. The University of Fribourg is a bilingual university (German and French) and the candidate should master at least one of these languages as well as have a very good knowledge of English.

    To apply, please send a complete CV, a motivation letter and some references to Prof. Bernard Ries: More information about the DS&OR group can be found under

    Formal evaluation of the applications will begin on March 31, 2020. Applications beyond that date might be considered.

  • Jan 2020: Paper accepted in Theoretical Computer Science!

    Our paper "Semitotal Domination: New hardness results and a polynomial-time algorithm for graphs of bounded mim-width", E. Galby, A. Munaro, B. Ries, has been accepted in Theoretical Computer Science. This work has been done mainly while Andrea Munaro was a postdoctoral research fellow in our group!

  • Sept 2019: Industrial visit at Vifor

    DSOR and Digitalization and Information Systems research groups at Vifor

    We had the opportunity to visit Vifor's production site at Villars-sur-Glâne on Sept. 11. Thanks a lot to David Peguiron, Head of Manufacturing VsG, for giving us an excellent guided tour through the production facility and for discussing with us the current challenges of manufacturing in the digital age. 

  • Sept 2019: Felix Mann joins our group

    On Sept 1st, 2019, Felix Mann joined our group as PhD student.  Welcome Felix!

  • Sept 2019: New publication in EURO Journal on Computational Optimization on large-scale employee scheduling

    The article A decomposition-based heuristic for large employee scheduling problems with inter-department transfers was accepted for publication in the journal EURO Journal on Computational Optimization. This is joint work of Reinhard Bürgy with Dalia Attia, Guy Desaulniers and François Soumis from Polytechnique Montreal and GERAD.


    The article is accessible on



    We consider a personalized employee scheduling problem with characteristics present in retail stores consisting of multiple departments. In the setting under study, each department generally covers its demand in employees over the planning horizon of a week by assigning shifts to its own staff. However, the employees can also be transferred to other departments under certain conditions for executing entire shifts or parts of shifts there. The transfer feature enables to improve the overall schedule quality considerably when compared to the nontransfer case. Given the complexity of the problem, we propose a three-phase decomposition-based heuristic. In the first phase, we consider each department separately and solve a simplified version of the mono-department scheduling problems. From the obtained solutions, we deduce inter-department shifts that could potentially reduce the overall cost. This is examined in the second phase by resolving the scheduling problem of the first phase where the deduced inter-department shifts are included. In this phase, however, we decompose the scheduling problem by time, looking at each day separately. From the obtained schedules, we then devise inter-department demand curves, which specify the number of transfers between departments over time. In the third phase, we decompose the initial scheduling problem into mono-department problems using these inter-department demand curves. Consequently, our approach makes it possible to solve mono-department optimization problems to get an overall schedule while still benefiting from the employee transfer feature. In all three phases, the scheduling problems are formulated as mixed-integer linear programs. We show through extensive computational experiments on instances with up to 25 departments and 1000 employees that the method provides high-quality solutions within reasonable computation times.

  • Aug 2019: Zakir Deniz joins DS&OR

    Zakir Deniz joins our group as a postdoc for 4 months! Welcome Zakir!

  • June 2019: Paper accepted at MFCS 2019!

    Our paper "Reducing the domination number of graphs via edge contractionsE. Galby, P.T. Lima, B. Ries" has been accepted at the MFCS conference 2019! These results were obtained while Paloma de Lima was visiting our University.

  • June 2019: Paper accepted in Discrete Mathematics!

    Our paper "Detecting strong cliques, A. Hujdurovic, M. Milanic, B. Ries" has been accepted for publication in Discrete Mathematics! These results were obtained while B. Ries was visiting M. Milanic and A. Hujdurovic in Koper (Slovenia).

  • Feb 2019: Paper accepted in Information processing Letters!

    Our paper "Classifying k-edge colouring for H-free graphs, E. Galby, P. T. Lima, D. Paulusma, B. Ries" just appeared in Information Processing Letters! These results were obtained while Paloma Lima and Daniel Paulusma were visiting our group in 2018!

  • Feb 2019: David Schindl joins DS&OR for five years!

    David Schindl, maître d'enseignement at HEG Geneva, will join our group on February 1st, 2019 for five years. He will be working at 40% as a maître assistant and collaborate with us on several projects. Furthermore, he will be giving the lecture Graph Theory & Applications from 2019 on. Welcome David!