<table><caption>Table 3 For the first four teams: their final score, how many times they computed the best solution, and how many times their solution is x% close to the best solution, on the private set.</caption><thead><tr><th>Team name</th><th>Cumul. ratio</th><th># Best</th><th># ≤ 0.1%</th><th># ≤ 0.5%</th><th># ≤ 1%</th><th># ≤ 2%</th><th># ≤ 3%</th></tr></thead><tbody><tr><td>CIMAT Team</td><td>99.93</td><td>34</td><td>49</td><td>95</td><td>100</td><td>100</td><td>100</td></tr><tr><td>reko</td><td>99.85</td><td>78</td><td>81</td><td>88</td><td>93</td><td>99</td><td>100</td></tr><tr><td>MJG</td><td>99.80</td><td>24</td><td>58</td><td>87</td><td>95</td><td>98</td><td>100</td></tr><tr><td>CUiB</td><td>99.72</td><td>19</td><td>48</td><td>82</td><td>89</td><td>97</td><td>100</td></tr></tbody></table>

## 5 PACE organization

In September 2018, the PACE 2018 Program Committee transferred to the Steering Committee. The Steering Committee and the PACE 2018 Program Committee are as follows.

<table><tbody><tr><td rowspan="10">Steering committee:</td><td>Édouard Bonnet</td><td>ENS Lyon</td></tr><tr><td>Holger Dell</td><td>Saarland Informatics Campus</td></tr><tr><td>Thore Husfeldt</td><td>ITU Copenhagen & Lund University</td></tr><tr><td>Bart M. P. Jansen (chair)</td><td>Eindhoven University of Technology</td></tr><tr><td>Petteri Kaski</td><td>Aalto University</td></tr><tr><td>Christian Komusiewicz</td><td>Philipps-Universität Marburg</td></tr><tr><td>Frances A. Rosamond</td><td>University of Bergen</td></tr><tr><td>Florian Sikora</td><td>Paris-Dauphine University</td></tr><tr><td rowspan="2">Track A, B, C:</td><td>Édouard Bonnet</td><td>ENS Lyon</td></tr><tr><td>Florian Sikora</td><td>Paris-Dauphine University</td></tr></tbody></table>

The Program Committee of PACE 2019 will be chaired by Johannes Fichte (TU Dresden) and Markus Hecher (TU Vienna).

## 6 Conclusion

We thank all the participants for their enthusiasm and look forward to the next PACE. We are particularly happy that this edition attracted many people outside the parameterized complexity community, and wish that this will continue for the future editions.

We welcome anyone who is interested to add their name to the mailing list on the website [36] to receive PACE updates and join the discussion. In particular, plans for PACE 2019 will be posted there.

## References

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14 Holger Dell, Christian Komusiewicz, Nimrod Talmon, and Mathias Weller. The PACE 2017 Parameterized Algorithms and Computational Experiments Challenge: The Second Iteration. In *12th International Symposium on Parameterized and Exact Computation, IPEC 2017, September 6-8, 2017, Vienna, Austria*, pages 30:1–30:12, 2017. doi:10.4230/LIPIcs.IPEC.2017.30.

15 Michael Dom, Daniel Lokshtanov, and Saket Saurabh. Kernelization Lower Bounds Through Colors and IDs. *ACM Trans. Algorithms*, 11(2):13:1–13:20, 2014. doi:10.1145/2650261.

16 Stuart E. Dreyfus and Robert A. Wagner. The Steiner problem in graphs. *Networks*, 1(3):195–207, 1971.
3 Max Bannach, Sebastian Berndt, and Thorsten Ehlers. Jdrasil: A Modular Library for Computing Tree Decompositions. In *Costas S. Iliopoulos, Solon P. Pissis, Simon J. Puglisi, and Rajeev Raman, editors, Proceedings of the 16th International Symposium on Experimental Algorithms (SEA 2017), volume 75 of Leibniz International Proceedings in Informatics (LIPIcs)*, pages 28:1–28:21, Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.SEA.2017.28.

4 Max Bannach, Sebastian Berndt, Thorsten Ehlers, and Dirk Nowotka. SAT-encodings of tree decompositions. *SAT COMPETITION 2018*, page 72, 2018.

5 Sebastian Berndt. Computing Tree Width: From Theory to Practice and Back. In *Conference on Computability in Europe*, pages 81–88. Springer, 2018.

6 Andreas Björklund, Thore Husfeldt, Petteri Kaski, and Mikko Koivisto. Fourier meets möbius: fast subset convolution. In *Proceedings of the 39th Annual ACM Symposium on Theory of Computing, San Diego, California, USA, June 11-13, 2007*, pages 67–74, 2007. doi:10.1145/1250790.1250801.

7 Johannes Blum and Sabine Storandt. Computation and Growth of Road Network Dimensions. In *International Computing and Combinatorics Conference*, pages 230–241. Springer, 2018.

8 Hans L. Bodlaender, Marek Cygan, Stefan Kratsch, and Jesper Nederlof. Deterministic single exponential time algorithms for connectivity problems parameterized by treewidth. *Inf. Comput.*, 243:86–111, 2015. doi:10.1016/j.ic.2014.12.008.

9 Jarosław Byrka, Fabrizio Grandoni, Thomas Rothvoß, and Laura Sanità. Steiner tree approximation via iterative randomized rounding. *J. ACM*, 60(1):6:1–6:33, 2013. doi:10.1145/2432622.2432628.

10 Miroslav Chlebík and Janka Chlebíková. The Steiner tree problem on graphs: Inapproximability results. *Theor. Comput. Sci.*, 406(3):207–214, 2008. doi:10.1016/j.tcs.2008.06.046.

11 Marek Cygan, Fedor V. Fomin, Łukasz Kowalik, Daniel Lokshtanov, Dániel Marx, Marcin Pilipczuk, Michał Pilipczuk, and Saket Saurabh. *Parameterized Algorithms*. Springer, 2015. doi:10.1007/978-3-319-21275-3.

12 Marek Cygan, Jesper Nederlof, Marcin Pilipczuk, Michał Pilipczuk, Johan M. M. van Rooij, and Jakub Onufry Wojtaszczyk. Solving Connectivity Problems Parameterized by Treewidth in Single Exponential Time. In *IEEE 52nd Annual Symposium on Foundations of Computer Science, FOCS 2011, Palm Springs, CA, USA, October 22-25, 2011*, pages 150–159, 2011. doi:10.1109/FOCS.2011.23.

13 Holger Dell, Thore Husfeldt, Bart M. P. Jansen, Petteri Kaski, Christian Komusiewicz, and Frances A. Rosamond. The First Parameterized Algorithms and Computational Experiments Challenge. In *Jiong Guo and Danny Hermelin, editors, Proceedings of the 11th International Symposium on Parameterized and Exact Computation (IPEC 2016)*, volume 63 of *Leibniz International Proceedings in Informatics (LIPIcs)*, pages 30:1–30:9, Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.IPEC.2016.30.

14 Holger Dell, Christian Komusiewicz, Nimrod Talmon, and Mathias Weller. The PACE 2017 Parameterized Algorithms and Computational Experiments Challenge: The Second Iteration. In *12th International Symposium on Parameterized and Exact Computation, IPEC 2017, September 6-8, 2017, Vienna, Austria*, pages 30:1–30:12, 2017. doi:10.4230/LIPIcs.IPEC.2017.30.

15 Michael Dom, Daniel Lokshtanov, and Saket Saurabh. Kernelization Lower Bounds Through Colors and IDs. *ACM Trans. Algorithms*, 11(2):13:1–13:20, 2014. doi:10.1145/2650261.

16 Stuart E. Dreyfus and Robert A. Wagner. The Steiner problem in graphs. *Networks*, 1(3):195–207, 1971.
17 Eugene F. Dumitrescu, Allison L. Fisher, Timothy D. Goodrich, Travis S. Humble, Blair D. Sullivan, and Andrew L. Wright. Benchmarking treewidth as a practical component of tensor-network-based quantum simulation. arXiv preprint arXiv:1807.04599, 2018.

18 Pavel Dvořák, Andreas Emil Feldmann, Dušan Knop, Tomáš Masařík, Tomáš Toufar, and Pavel Veselý. Parameterized Approximation Schemes for Steiner Trees with Small Number of Steiner Vertices. In Rolf Niedermeier and Brigitte Vallée, editors, *35th Symposium on Theoretical Aspects of Computer Science, STACS 2018, February 28 to March 3, 2018, Caen, France*, volume 96 of *LIPIcs*, pages 26:1–26:15. Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik, 2018. doi:10.4230/LIPIcs.STACS.2018.26.

19 Ranel E. Erickson, Clyde L. Monma, and Arthur F. Veinott Jr. Send-and-Split Method for Minimum-Concave-Cost Network Flows. *Math. Oper. Res.*, 12(4):634–664, 1987. doi: 10.1287/moor.12.4.634.

20 Johannes K Fichte, Markus Hecher, Neha Lodha, and Stefan Szeider. An SMT Approach to Fractional Hypertree Width. technical report, 2018.

21 Johannes Klaus Fichte, Markus Hecher, Michael Morak, and Stefan Woltran. Answer Set Solving with Bounded Treewidth Revisited. In Marcello Balduccini and Tomi Janhunen, editors, *Proceedings of 14th International Conference on Logic Programming and Nonmonotonic Reasoning - (LPNMR 2017)*, volume 10377 of *Lecture Notes in Computer Science*, pages 132–145. Springer, 2017. doi:10.1007/978-3-319-61660-5_13.

22 Johannes Klaus Fichte, Markus Hecher, Michael Morak, and Stefan Woltran. DynASP2.5: Dynamic programming on tree decompositions in action. In *Proceedings of the 12th International Symposium on Parameterized and Exact Computation (IPEC 2017)*, Leibniz International Proceedings in Informatics (LIPIcs), Dagstuhl, Germany, 2017. doi: 10.4230/LIPIcs.IPEC.2017.17.

23 Johannes Klaus Fichte, Markus Hecher, Stefan Woltran, and Markus Zisser. Weighted Model Counting on the GPU by Exploiting Small Treewidth. In *26th Annual European Symposium on Algorithms, ESA 2018, August 20-22, 2018, Helsinki, Finland*, pages 28:1–28:16, 2018. doi:10.4230/LIPIcs.ESA.2018.28.

24 Bernhard Fuchs, Walter Kern, Daniel Mölle, Stefan Richter, Peter Rossmanith, and Xin-hui Wang. Dynamic Programming for Minimum Steiner Trees. *Theory Comput. Syst.*, 41(3):493–500, 2007. doi:10.1007/s00224-007-1324-4.

25 Serge Gaspers, Joachim Gudmundsson, Mitchell Jones, Julián Mestre, and Stefan Rümmele. Turbocharging Treewidth Heuristics. In Jiong Guo and Danny Hermelin, editors, *Proceedings of the 11th International Symposium on Parameterized and Exact Computation (IPEC 2016)*, volume 63 of *Leibniz International Proceedings in Informatics (LIPIcs)*, pages 13:1–13:13, Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.IPEC.2016.13.

26 Martin Josef Geiger. Implementation of a Metaheuristic for the Steiner Tree Problem in Graphs. Mendeley Data. v1. doi:10.17632/yf9vpkgwdr.1.

27 Edgar N. Gilbert and Henry O. Pollak. Steiner minimal trees. *SIAM Journal on Applied Mathematics*, 16(1):1–29, 1968.

28 L.W. van der Graaff. Dynamic programming on Nice Tree Decompositions. Master's thesis, Utrecht University, 2015. URL: https://dspace.library.uu.nl/handle/1874/309652.

29 Stefan Hougardy, Jannik Silvanus, and Jens Vygen. Dijkstra meets Steiner: A fast exact goal-oriented Steiner tree algorithm. *Math. Program. Comput.*, 9(2):135–202, 2017. doi: 10.1007/s12532-016-0110-1.

30 Frank K. Hwang, Dana S. Richards, and Pawel Winter. *The Steiner tree problem*, volume 53. Elsevier, 1992.

31 Yoichi Iwata. Linear-Time Kernelization for Feedback Vertex Set. In Ioannis Chatzigiannakis, Piotr Indyk, Fabian Kuhn, and Anca Muscholl, editors, *Proceedings of the 44th International Colloquium on Automata, Languages, and Programming (ICALP 2017)*,
17 Eugene F. Dumitrescu, Allison L. Fisher, Timothy D. Goodrich, Travis S. Humble, Blair D. Sullivan, and Andrew L. Wright. Benchmarking treewidth as a practical component of tensor-network-based quantum simulation. arXiv preprint arXiv:1807.04599, 2018.

18 Pavel Dvořák, Andreas Emil Feldmann, Dušan Knop, Tomáš Masařík, Tomáš Toufar, and Pavel Veselý. Parameterized Approximation Schemes for Steiner Trees with Small Number of Steiner Vertices. In Rolf Niedermeier and Brigitte Vallée, editors, *35th Symposium on Theoretical Aspects of Computer Science, STACS 2018, February 28 to March 3, 2018, Caen, France*, volume 96 of *LIPIcs*, pages 26:1–26:15. Schloss Dagstuhl - Leibniz-Zentrum fuer Informatik, 2018. doi:10.4230/LIPIcs.STACS.2018.26.

19 Ranel E. Erickson, Clyde L. Monma, and Arthur F. Veinott Jr. Send-and-Split Method for Minimum-Concave-Cost Network Flows. *Math. Oper. Res.*, 12(4):634–664, 1987. doi: 10.1287/moor.12.4.634.

20 Johannes K Fichte, Markus Hecher, Neha Lodha, and Stefan Szeider. An SMT Approach to Fractional Hypertree Width. technical report, 2018.

21 Johannes Klaus Fichte, Markus Hecher, Michael Morak, and Stefan Woltran. Answer Set Solving with Bounded Treewidth Revisited. In Marcello Balduccini and Tomi Janhunen, editors, *Proceedings of 14th International Conference on Logic Programming and Nonmonotonic Reasoning - (LPNMR 2017)*, volume 10377 of *Lecture Notes in Computer Science*, pages 132–145. Springer, 2017. doi:10.1007/978-3-319-61660-5_13.

22 Johannes Klaus Fichte, Markus Hecher, Michael Morak, and Stefan Woltran. DynASP2.5: Dynamic programming on tree decompositions in action. In *Proceedings of the 12th International Symposium on Parameterized and Exact Computation (IPEC 2017)*, Leibniz International Proceedings in Informatics (LIPIcs), Dagstuhl, Germany, 2017. doi: 10.4230/LIPIcs.IPEC.2017.17.

23 Johannes Klaus Fichte, Markus Hecher, Stefan Woltran, and Markus Zisser. Weighted Model Counting on the GPU by Exploiting Small Treewidth. In *26th Annual European Symposium on Algorithms, ESA 2018, August 20-22, 2018, Helsinki, Finland*, pages 28:1–28:16, 2018. doi:10.4230/LIPIcs.ESA.2018.28.

24 Bernhard Fuchs, Walter Kern, Daniel Mölle, Stefan Richter, Peter Rossmanith, and Xin-hui Wang. Dynamic Programming for Minimum Steiner Trees. *Theory Comput. Syst.*, 41(3):493–500, 2007. doi:10.1007/s00224-007-1324-4.

25 Serge Gaspers, Joachim Gudmundsson, Mitchell Jones, Julián Mestre, and Stefan Rümmele. Turbocharging Treewidth Heuristics. In Jiong Guo and Danny Hermelin, editors, *Proceedings of the 11th International Symposium on Parameterized and Exact Computation (IPEC 2016)*, volume 63 of *Leibniz International Proceedings in Informatics (LIPIcs)*, pages 13:1–13:13, Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.IPEC.2016.13.

26 Martin Josef Geiger. Implementation of a Metaheuristic for the Steiner Tree Problem in Graphs. Mendeley Data. v1. doi:10.17632/yf9vpkgwdr.1.

27 Edgar N. Gilbert and Henry O. Pollak. Steiner minimal trees. *SIAM Journal on Applied Mathematics*, 16(1):1–29, 1968.

28 L.W. van der Graaff. Dynamic programming on Nice Tree Decompositions. Master's thesis, Utrecht University, 2015. URL: https://dspace.library.uu.nl/handle/1874/309652.

29 Stefan Hougardy, Jannik Silvanus, and Jens Vygen. Dijkstra meets Steiner: A fast exact goal-oriented Steiner tree algorithm. *Math. Program. Comput.*, 9(2):135–202, 2017. doi: 10.1007/s12532-016-0110-1.

30 Frank K. Hwang, Dana S. Richards, and Pawel Winter. *The Steiner tree problem*, volume 53. Elsevier, 1992.

31 Yoichi Iwata. Linear-Time Kernelization for Feedback Vertex Set. In Ioannis Chatzigiannakis, Piotr Indyk, Fabian Kuhn, and Anca Muscholl, editors, *Proceedings of the 44th International Colloquium on Automata, Languages, and Programming (ICALP 2017)*,
volume 80 of *Leibniz International Proceedings in Informatics (LIPIcs)*, pages 68:1–68:14, 2017. doi:10.4230/LIPIcs.ICALP.2017.68.

32 Krzysztof Kiljan and Marcin Pilipczuk. Experimental Evaluation of Parameterized Algorithms for Feedback Vertex Set. *arXiv preprint arXiv:1803.00925*, 2018.

33 Neha Lodha, Sebastian Ordyniak, and Stefan Szeider. SAT-encodings for special treewidth and pathwidth. In *Proceedings of the 20th International Conference on Theory and Applications of Satisfiability Testing (SAT 2017)*, volume 10491 of *Lecture Notes in Computer Science*, pages 429–445. Springer, 2017. doi:10.1007/978-3-319-66263-3_27.

34 Daniel Mölle, Stefan Richter, and Peter Rossmanith. Enumerate and Expand: Improved Algorithms for Connected Vertex Cover and Tree Cover. *Theory Comput. Syst.*, 43(2):234–253, 2008. doi:10.1007/s00224-007-9089-3.

35 Networks project, 2017. URL: http://www.thenetworkcenter.nl.

36 Parameterized Algorithms and Computational Experiments website, 2015–2018. URL: https://pacechallenge.org.

37 Daniel Rehfeldt. A generic approach to solving the Steiner tree problem and variants. Master's thesis, Technische Universität Berlin, Germany, 2015. URL: http://nbn-resolving.de/urn:nbn:de:0297-zib-57817.

38 Gabriel Robins and Alexander Zelikovsky. Tighter bounds for graph Steiner tree approximation. *SIAM Journal on Discrete Mathematics*, 19(1):122–134, 2005.

39 Ondřej Suchý. Extending the Kernel for Planar Steiner Tree to the Number of Steiner Vertices. *Algorithmica*, 79(1):189–210, 2017. doi:10.1007/s00453-016-0249-1.

40 Hisao Tamaki. Positive-Instance Driven Dynamic Programming for Treewidth. In Kirk Pruhs and Christian Sohler, editors, *25th Annual European Symposium on Algorithms (ESA 2017)*, volume 87 of *Leibniz International Proceedings in Informatics (LIPIcs)*, pages 68:1–68:13, Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.ESA.2017.68.

41 Tom C. van der Zanden and Hans L. Bodlaender. Computing Treewidth on the GPU. In *Proceedings of the 12th International Symposium on Parameterized and Exact Computation (IPEC 2017)*, Leibniz International Proceedings in Informatics (LIPIcs), Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.IPEC.2017.29.

42 Rim van Wersch and Steven Kelk. ToTo: An open database for computation, storage and retrieval of tree decompositions. *Discrete Applied Mathematics*, 217:389–393, 2017. doi:10.1016/j.dam.2016.09.023.
volume 80 of *Leibniz International Proceedings in Informatics (LIPIcs)*, pages 68:1–68:14, 2017. doi:10.4230/LIPIcs.ICALP.2017.68.

32 Krzysztof Kiljan and Marcin Pilipczuk. Experimental Evaluation of Parameterized Algorithms for Feedback Vertex Set. *arXiv preprint arXiv:1803.00925*, 2018.

33 Neha Lodha, Sebastian Ordyniak, and Stefan Szeider. SAT-encodings for special treewidth and pathwidth. In *Proceedings of the 20th International Conference on Theory and Applications of Satisfiability Testing (SAT 2017)*, volume 10491 of *Lecture Notes in Computer Science*, pages 429–445. Springer, 2017. doi:10.1007/978-3-319-66263-3_27.

34 Daniel Mölle, Stefan Richter, and Peter Rossmanith. Enumerate and Expand: Improved Algorithms for Connected Vertex Cover and Tree Cover. *Theory Comput. Syst.*, 43(2):234–253, 2008. doi:10.1007/s00224-007-9089-3.

35 Networks project, 2017. URL: http://www.thenetworkcenter.nl.

36 Parameterized Algorithms and Computational Experiments website, 2015–2018. URL: https://pacechallenge.org.

37 Daniel Rehfeldt. A generic approach to solving the Steiner tree problem and variants. Master's thesis, Technische Universität Berlin, Germany, 2015. URL: http://nbn-resolving.de/urn:nbn:de:0297-zib-57817.

38 Gabriel Robins and Alexander Zelikovsky. Tighter bounds for graph Steiner tree approximation. *SIAM Journal on Discrete Mathematics*, 19(1):122–134, 2005.

39 Ondřej Suchý. Extending the Kernel for Planar Steiner Tree to the Number of Steiner Vertices. *Algorithmica*, 79(1):189–210, 2017. doi:10.1007/s00453-016-0249-1.

40 Hisao Tamaki. Positive-Instance Driven Dynamic Programming for Treewidth. In Kirk Pruhs and Christian Sohler, editors, *25th Annual European Symposium on Algorithms (ESA 2017)*, volume 87 of *Leibniz International Proceedings in Informatics (LIPIcs)*, pages 68:1–68:13, Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.ESA.2017.68.

41 Tom C. van der Zanden and Hans L. Bodlaender. Computing Treewidth on the GPU. In *Proceedings of the 12th International Symposium on Parameterized and Exact Computation (IPEC 2017)*, Leibniz International Proceedings in Informatics (LIPIcs), Dagstuhl, Germany, 2017. doi:10.4230/LIPIcs.IPEC.2017.29.

42 Rim van Wersch and Steven Kelk. ToTo: An open database for computation, storage and retrieval of tree decompositions. *Discrete Applied Mathematics*, 217:389–393, 2017. doi:10.1016/j.dam.2016.09.023.
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