News

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

  • Meritxell Pacheco Paneque joins DS&OR in January 2021 as Senior Researcher

    On January 2021, Dr. Meritxell Pacheco Paneque joins our group as Senior Researcher to work on our Innosuisse project on efficient and sustainable waste collection. Meritxell recently finished her PhD at EPFL's Transport and Mobility Laboratory. We are looking forward to welcoming here soon here in Fribourg!

  • September 20: Paper accepted in Discrete Mathematics

    Our paper "Reducing the domination number of graphs via edge contractions and vertex deletions" E. Galby, P. T. Lima, B. Ries, has been accepted in Discrete Mathematics and is available via Open Access here!

  • July 20: Paper accepted in Discrete Applied Mathematics

    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 Discrete Applied Mathematics. This work has been done mainly while Andrea Munaro was a postdoctoral research fellow in our group!

  • Article on the precedence-constrained class sequencing problem accepted for publication in Computers & Operations Research

    The article An exact dynamic programming algorithm for the precedence-constrained class sequencing problem was accepted for publication in the journal Computers & Operations Research. This is joint work of Reinhard Bürgy with Alain Hertz and Pierre Baptiste from Polytechnique Montreal and GERAD.

     

    The working paper of this article is freely accessible on https://www.gerad.ca/fr/papers/G-2017-82.

     

    Abstract:
    This article discusses the precedence-constrained class sequencing problem (PCCSP). In scheduling terms, this is a one-machine scheduling problem with precedence constraints and setups with the goal of minimizing the number of setups. From a practical perspective, PCCSP covers a wide range of applications such as, for example, scheduling problems in systems where multipurpose processors need retooling to switch from one operation to another. Previous research has shown that PCCSP is difficult to solve from both a theoretical and computational perspective, and only little research has been conducted on computational methods. This article bridges this gap by proposing a dynamic programming algorithm for solving PCCSP exactly. It comprises specialized dominance rules, lower bound computations, propagation algorithms, and heuristics that successfully exploit the problem's structure. Based on extensive numerical experiments, we analyze the algorithm in detail and show that it outperforms mixed-integer programming and constraints programming models.

  • Esther Galby defended her PhD thesis successfully!

    Latest publications

    Congratulations to Esther who defended her PhD tehsis successfully on June 29, 2020. The jury was impressed by her work and her presentation. Well done Esther!

  • June 2020: Industrial project with CSL Behring, Bern

    Reinhard Bürgy and David Schindl started a new industrial project with CSL Behring, Bern.  The goal of the project is to develop a decision support tool helping to find opimized production schedules.

  • Felicia Lucke and Narmina Baghirova will join our group in September 2020!

    Felicia Lucke, currently doing her Master thesis at the University of Ulm (Germany), and Narmina Baghirova, currently doing her Master thesis at the University of Primorska (Slovenia), will both join our group as PhD students in September 2020. We are looking forward to welcoming them!

  • Jan 2020: Paper accepted in Theoretical Computer Science!

    Our paper "CPG graphs: some structural and hardness results", 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!

  • Maria Grazia Speranza: Docteure Honoris Causa of the University of Fribourg

    During the Dies Academicus 2019, Maria Grazia Speranza was given the title of Docteure Honoris Causa from the Faculty of Management, Economics and Social Sciences. An interview (in italian) as well as some pictures from teh ceremony can be found here.

  • 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 https://doi.org/10.1007/s13675-019-00119-3.

     

    Abstract:

    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!