Christopher Hojny

Eindhoven University of Technology
Department of Mathematics and Computer Science
Combinatorial Optimization Group

P.O. Box 513
5600 MB Eindhoven

Office: MF 4.101

Phone: +31 40-247 8330

Email:

Github: https://github.com/christopherhojny

Curriculum Vitae

A detailed CV can be found here.

Office Hour

by appointment

Research Interests

  • Symmetry in Integer Programs
  • Measuring Abstract Properties of Integer Programs
  • Graph Coloring Problems
  • Knapsack Polytopes
  • Polyhedral Combinatorics

Publications

  • Integer Programming Formulations for Compact Single Round Robin Tournaments, with Jasper van Doornmalen, Roel Lambers, and Frits C.R. Spieksma, Proceedings of the 13th International Conference on the Practice and Theory of Automated Timetabling - PATAT 2022, P. de Causmaecker, E. Özcan, G. Vanden Berghe, Eds. vol. 3, 208-210, 2022. DOI: available here
  • A Simple Method for Convex Optimization in the Oracle Model, with Daniel Dadush, Sophie Huiberts, and Stefan Weltge, IPCO 2022, Conference Proceedings, K. Aardal and L. Sanità, Eds. vol. 1, 154-167, 2022. DOI: 10.1007/978-3-031-06901-7_12
  • Characterizing and computing weight-equitable partitions of graphs, with Aida Abiad and Sjanne Zeijlemaker, Linear Algebra and Its Applications, 2022, 645, 30-51, DOI: 10.1016/j.laa.2022.03.003
  • A Hybrid Model to Find Schedules for Double Round Robin Tournaments With Side Constraints, with Jasper van Doornmalen, Roel Lambers, and Frits C.R. Spieksma, Proceedings of the 13th International Conference on the Practice and Theory of Automated Timetabling - PATAT 2022, P. de Causmaecker, E. Özcan, G. Vanden Berghe, Eds. vol. 2, 412-419, 2021. DOI: available here
  • Computational Aspects of Relaxation Complexity: Possibilities and Limitations, with Gennadiy Averkov and Matthias Schymura, Mathematical Programming, 2021. DOI: 10.1007/s10107-021-01754-8
  • Computational Aspects of Relaxation Complexity, with Gennadiy Averkov and Matthias Schymura, IPCO 2021, Conference Proceedings, M. Singh and D. P. Williamson, Eds. vol. 1, 368-382, 2021. DOI: 10.1007/978-3-030-73879-2_26
  • Strong IP Formulations Need Large Coefficients, Discrete Optimization, 2021, 39, DOI: 10.1016/j.disopt.2021.100624
  • Mixed-Integer Programming Techniques for the Connected Max-k-Cut Problem, with Imke Joormann, Hendrik Lüthen, and Martin Schmidt, Mathematical Programming Computation, 2021, 13, 75-132, DOI: 10.1007/s12532-020-00186-3
  • Polynomial Size IP Formulations of Knapsack May Require Exponentially Large Coefficients, Operations Research Letters, 2020, 48, 612-618, DOI: 10.1016/j.orl.2020.07.013
  • The SCIP Optimization Suite 7.0, with Gerald Gamrath, Daniel Anderson, Ksenia Bestuzheva, Wei-Kun Chen, Leon Eifler, Maxime Gasse, Patrick Gemander, Ambros Gleixner, Leona Gottwald, Katrin Halbig, Gregor Hendel, Thorsten Koch, Pierre Le Bodic, Stephen J. Maher, Frederic Matter, Matthias Miltenberger, Erik Mühmer, Benjamin Müller, Marc E. Pfetsch, Franziska Schlösser, Felipe Serrano, Yuji Shinano, Christine Tawfik, Stefan Vigerske, Fabian Wegscheider, Dieter Weninger, and Jakob Witzig, available at optimization online, 2020
  • Packing, Partitioning, and Covering Symresacks, to appear in Discrete Applied Mathematics, 2020, 283, 689-717, DOI: 10.1016/j.dam.2020.03.002
  • Knapsack Polytopes – A Survey, with Tristan Gally, Oliver Habeck, Hendrik Lüthen, Frederic Matter, Marc E. Pfetsch, and Andreas Schmitt, Annals of Operations Research, 2020, 292, 469-517, DOI: 10.1007/s10479-019-03380-2
  • Sparsity of Integer Formulations for Binary Programs, with Hendrik Lüthen and Marc E. Pfetsch, Operations Research Letters, 2019, 47(5), 348-352,DOI: 10.1016/j.orl.2019.06.001
  • Polytopes Associated with Symmetry Handling, with Marc E. Pfetsch, Mathematical Programming, 2019, 175(1), 197-240, DOI: 10.1007/s10107-018-1239-7
  • The SCIP Optimization Suite 6.0, with Ambros Gleixner, Michael Bastubbe, Leon Eifler, Tristan Gally, Gerald Gamrath, Robert Lion Gottwald, Gregor Hendel, Thorsten Koch, Marco E. Lübbecke, Stephen J. Maher, Matthias Miltenberger, Benjamin Müller, Marc E. Pfetsch, Christian Puchert, Daniel Rehfeldt, Franziska Schlösser, Christoph Schubert, Felipe Serrano, Yuji Shinano, Jan Merlin Viernickel, Matthias Walter, Fabian Wegschneider, Jonas T. Witt, and Jakob Witzig, available at kobv, 2018
  • Extended Formulations for Column Constrained Orbitopes, with Marc E. Pfetsch and Andreas Schmitt, Operations Research Proceedings 2017, N. Kliewer, J. F. Ehmke, and R. Borndörfer, Eds. vol. 1, pp. 197-204, 2018. DOI: 10.1007/978-3-319-89920-6
  • The SCIP Optimization Suite 5.0, with Ambros Gleixner, Leon Eifler, Tristan Gally, Gerald Gamrath, Patrick Gemander, Robert Lion Gottwald, Gregor Hendel, Thorsten Koch, Matthias Miltenberger, Benjamin Müller, Marc E. Pfetsch, Christian Puchert, Daniel Rehfeldt, Franziska Schlösser, Felipe Serrano, Yuji Shinano, Jan Merlin Viernickel, Stefan Vigerske, Dieter Weninger, Jonas T. Witt, and Jakob Witzig, available at kobv, 2017
  • A Polyhedral Investigation of Star Colorings, with Marc E. Pfetsch, Discrete Applied Mathematics, 2016, 208, 59-78, DOI: 10.1016/j.dam.2016.03.003

Preprints

  • A unfified framework for symmetry handling, with Jasper van Doornmalen, preprint available at optimization online, 2022
  • A flow-based formulation for parallel machine scheduling using decision diagrams, with Daniel Kowalczyk, Roel Leus, and Stefan Røpke, preprint available at arXiv, 2022
  • The role of rationality in integer-programming relaxations, with Manuel Aprile, Gennadiy Averkov, and Marco Di Summa, preprint available at optimization online, 2022
  • Efficient MIP Techniques for Computing the Relaxation Complexity, with Gennadiy Averkov and Matthias Schymura, preprint available at optimization online, 2022
  • Mixed-Integer Programming Techniques for the Minimum Sum-of-Squares Clustering Problem, with Jan Pablo Burgard, Carina Moreira Costa, Thomas Kleinert, and Martin Schmidt, preprint available at optimization online, 2022
  • Efficient Propagation Techniques for Handling Cyclic Symmetries in Binary Programs, with Jasper van Doornmalen, preprint available at optimization online, 2022
  • Schreier-Sims Cuts meet Stable Set: Preserving Problem Structure when Handling Symmetries, with Marc E. Pfetsch and José Verschae, preprint available at optimization online, 2021
  • A Benders-type Approach for Robust Optimization of Kidney Exchanges under Full Recourse, with Danny Blom and Bart Smeulders, preprint available at arXiv, 2021
  • Integrality of Linearizations of Polynomials over Binary Variables using Additional Monomials, with Marc E. Pfetsch and Matthias Walter, preprint available at optimization online, 2019
  • On the Size of Integer Programs with Bounded Coefficients and Sparse Constraints, with Hendrik Lüthen and Marc E. Pfetsch, preprint available at optimization online, 2017

Problem Instances and Code

A collection of test instances used in some of the above publications can be found on this web page. The source code used in
some publications is available at github.

Dissertation

Symmetries in Binary Programs – A Polyhedral Perspective, sierke Verlag, 2018, available as soft cover and eBook.

Prizes

  • best dissertation award (Preis für hervorragende wissenschaftliche Leistungen) – Vereinigung von Freunden der Technischen Universität zu Darmstadt e.V.

Poster Presentations

  • MIP 2017, HEC Montréal, Canada, June 19, 2017: Constrained Symresacks – Symmetry Handling Exploiting Packing, Partitioning, and Covering Constraints, poster
  • MIP 2016, University of Miami, Coral Gables, FL, May 23, 2016: Symmetry Handling via {0,±1}-Inequalities, poster

Talks

  • OR Seminar, Tilburg University, Tilburg, The Netherlands, November 10, 2022 (invited talk): The role of rationality in integer programming formulations
  • Let's SCIP it! A workshop to celebrate 20 year of Solving Constraint Integer Program, Berlin, Germany, November 4, 2022: Symmetry Handling in SCIP---An Overview
  • INFORMS Annual Meeting 2022, Indianapolis, IN, October 17, 2022 (invited talk): Mixed-Integer Programming Techniques for the Minimum Sum-of-squares Clustering Problem
  • EURO2022, Espoo, Finland, July 5, 2022 (invited talk): Schreier-Sims Cuts meet Stable Set: Exploiting Problem Structure to Derive Symmetry Handling Inequalities
  • Workshop on Separating Integer Points in Polyhedra: Theory and Applications, Eindhoven, The Netherlands, July 1, 2022: Efficient MIP Techniques for Computing the Relaxation Complexity
  • EURO2021, Athens, Greece, July 14, 2021 (invited talk): Exploiting Subgroup Structures in Symmetry Handling
  • MIP Workshop 2021, online, May 26, 2021 (invited talk): Computational Aspects of Relaxation Complexity, video
  • IPCO 2021, Atlanta, Georgia, May 21, 2021: Computational Aspects of Relaxation Complexity, video
  • SCIP Online Workshop 2020, hosted by University of Exeter, Exeter, England, June 4, 2020 (invited talk): Mixed-Integer Programming Techniques for the Connected Max-k-Cut Problem, video
  • Workshop on Extended Formulations and Symmetries in Integer Programming, Universidad de O'Higgins, Rancagua, Chile, December 9, 2019 (invited talk): Symretopes and Symresacks: A Framework for Deriving Generic and Problem Specific Symmetry Handling Inequalities
  • OR 2019, Dresden, Germany, September 6, 2019: Strong IP Formulations Need Large Coefficients
  • ALOP Colloquium, Trier University, Germany, July 1, 2019 (invited talk): Symmetry Handling in Binary Programs: Combining Symretopes and Orbital Fixing
  • N&O Seminar, Centrum Wiskunde & Informatica (CWI), Netherlands, March 27, 2019 (invited talk): Strong IP Formulations Need Large Coefficients
  • Aussois COW 2019, Aussois, France, January 9, 2019: Strong IP Formulations Need Large Coefficients, slides
  • ISMP 2018, Bordeaux, France, July 3, 2018 (invited talk): Symmetry Breaking Polytopes: A Framwork for Symmetry Handling in Binary Programs
  • Aussois COW 2018, Aussois, France, January 12, 2018: Symmetry Breaking Polytopes: A Framwork for Symmetry Handling in Binary Programs, slides
  • OR 2017, Berlin, Germany, September 8, 2017 (invited talk): Polyhedral Symmetry Handling Techniques Exploiting Problem Information
  • FRICO 2017, Trier, Germany, August 16, 2017: On the Size of Integer Programs with Bounded Coefficients or Sparse Constraints
  • ICMS 2016, Berlin, Germany, July 14, 2016: Symmetry Handling in Binary Programs via Polyhedral Methods
  • Aussois COW 2016, Aussois, France, January 5, 2016: Polytopes Associated with Symmetry Handling, slides
  • ISMP 2015, Pittsburgh, PA, July 15, 2015 (invited talk): Polyhedral Symmetry Handling via Fundamental Domains
  • CTW 2015, Marmara University Istanbul, May 26, 2015: Symmetry Handling via Symmetry Breaking Polytopes
  • FRICO 2014, Otto von Guericke Universität Magdeburg, July 30, 2014: Polyhedral description of star colorings

Organization of Scientific Events

  • Workshop on "Separating Integer Points in Polyhedra: Theory and Applications": co-organizer
  • IPCO 2022: member of local organization committee

Teaching

  • spring 2022: Integer Programming
  • spring 2022: Advanced Linear Programming (Mastermath course, together with Leen Stougie)
  • spring 2021: Integer Programming
  • spring 2021: Advanced Linear Programming (Mastermath course, together with Leen Stougie)
  • spring 2020: Integer Programming (together with Rudi Pendavingh)
  • spring 2020: Advanced Linear Programming (Mastermath course, together with Leen Stougie)

Teaching Assistance

  • summer term 2019: Lineare Algebra II (Prof. Dr. M. Pfetsch)
  • winter term 2018/19: Lineare Algebra I (Prof. Dr. M. Pfetsch)
  • summer term 2018: Diskrete Optimierung (Prof. Dr. M. Pfetsch)
  • winter term 2017/18: Diskrete Mathematik (Prof. Dr. M. Pfetsch)
  • summer term 2017: Diskrete Optimierung (Prof. Dr. Y. Disser)
  • winter term 2016/17: Diskrete Mathematik (Prof. Dr. M. Pfetsch)
  • summer term 2016: Algorithmic Discrete Mathematics (PD Dr. A. Paffenholz)
  • winter term 2015/16: Einführung in die mathematische Software (PD Dr. A. Paffenholz)
  • summer term 2015: Algorithmic Discrete Mathematics (Prof. Dr. M. Pfetsch)
  • winter term 2014/15: Einführung in die mathematische Software (Dr. A. Paffenholz)
  • summer term 2014: Linear Algebra II (Prof. Dr. M. Otto)